DELTAS

Contents Introduction Classification of depositional environments Depositional environments Marginal-marine environments Deltaic system Controls on Delta Environment Sub-environments of delta Variation in delta morphology Processes in model delta Morphological units of delta Classification of Deltas Typical sequence Importance of delta Sedimentary structure in deltas Structural features of deltaic reservoir

Introduction To discuss deltas we should have great understanding

of depositional environment Depositional Environments Geomorphic setting in which a particular set of physical

chemical and biological processes operates to generate a certain kind of sedimentary deposit

Physical environment has ldquostaticrdquo and dynamic elements

1048708 Static basin geometry sediment composition water depth etc

1048708 Dynamic currents (wind water) precipitation climate

Chemical elements pH Eh salinity pCO2 etc Biological aspects activities of organisms (burrowing

skeletal particles etc) and their remains (eg peat)

Classification of Depositional Environments

Nonmarine Environments Colluvial and Alluvial fans Fluvial environments Lacustrine environments Aeolian environments

Costal(marginal marine) Environments River mouth environments Regressive river mouthsDeltas Transgressive river mouthsEstuaries Open shoreline(beach) environments Foreshore backshore

Marine Environments Shallow marine environments Shoreface Inner and outer shelf Deep marine environments Continental slope Abyssal plain(basin floor)

Depositional Environments1048708 Objective Use sedimentary deposits to

interpret depositional environments

1048708 Physical biological chemical parameters of

an environment combine to produce a body

of sediment characterized by specific

textural structural and compositional properties

1048708 Distinctive bodies of sediments or

sedimentary rocks are facies

What happenshellip What we wanthellip

Marginal marine environment

The marginal-marine(transitional) setting lies along the boundary between the continental and the marine depositional realms

It is a narrow zone dominated by Riverine Wave Tidal processes Salinities may range in different parts of the

system from fresh water through brackish water to supersaline depending upon the river discharge and climatic conditions

Deltaic system

The term ldquodeltardquo the Greek character was used to describe the mouth of Nile by Herodotus nearly 2500 years ago

A modern definition cites delta as ldquothe sub aerial and submerged contiguous sediment mass deposited in a body of water(ocean or lake) primarily by the action of a riverrdquo(Moore and Asquith1971p2563)

Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate

Shape of Delta The shape of a delta is not always the triangle that

suggested the name to Herodotus Delta shape is influenced by

a) Sediment input

b) Wave energy

c) Tidal energy

Controls on delta environment

Factors affecting delta regime morphology and facies (Elliot 1978a)

Magnitude of fluvial discharge

Delta morphology and sedimentary facies

Delta regime

Magnitude of wave and tidal currents

Climate tectonics subsidence sediment supply topography

Subenvironments of Delta Deltas are influenced by a complex combination

of fluvial and marine processes Each delta has more than a dozen distinct

environments of deposition These environments can be grouped into three

broad divisions

1 The delta plain with the meandering flood plains Swamps and beach complex

2 The steeper delta front

3 The broadly sloping prodelta which grades into the open shelf

Variations in delta morphology

The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics

Two main factors are the most important in determining the morphology of deltas

1) Effect of grain size

2) Depth of water in delta are going to deposit

(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits

(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands

(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies

(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water

Processes in a model delta Reduced to its simplest elements a delta forms

due to ldquounique hydrodynamic interactionrdquo between river water and seawater

There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater

Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth

Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Contents Introduction Classification of depositional environments Depositional environments Marginal-marine environments Deltaic system Controls on Delta Environment Sub-environments of delta Variation in delta morphology Processes in model delta Morphological units of delta Classification of Deltas Typical sequence Importance of delta Sedimentary structure in deltas Structural features of deltaic reservoir

Introduction To discuss deltas we should have great understanding

of depositional environment Depositional Environments Geomorphic setting in which a particular set of physical

chemical and biological processes operates to generate a certain kind of sedimentary deposit

Physical environment has ldquostaticrdquo and dynamic elements

1048708 Static basin geometry sediment composition water depth etc

1048708 Dynamic currents (wind water) precipitation climate

Chemical elements pH Eh salinity pCO2 etc Biological aspects activities of organisms (burrowing

skeletal particles etc) and their remains (eg peat)

Classification of Depositional Environments

Nonmarine Environments Colluvial and Alluvial fans Fluvial environments Lacustrine environments Aeolian environments

Costal(marginal marine) Environments River mouth environments Regressive river mouthsDeltas Transgressive river mouthsEstuaries Open shoreline(beach) environments Foreshore backshore

Marine Environments Shallow marine environments Shoreface Inner and outer shelf Deep marine environments Continental slope Abyssal plain(basin floor)

Depositional Environments1048708 Objective Use sedimentary deposits to

interpret depositional environments

1048708 Physical biological chemical parameters of

an environment combine to produce a body

of sediment characterized by specific

textural structural and compositional properties

1048708 Distinctive bodies of sediments or

sedimentary rocks are facies

What happenshellip What we wanthellip

Marginal marine environment

The marginal-marine(transitional) setting lies along the boundary between the continental and the marine depositional realms

It is a narrow zone dominated by Riverine Wave Tidal processes Salinities may range in different parts of the

system from fresh water through brackish water to supersaline depending upon the river discharge and climatic conditions

Deltaic system

The term ldquodeltardquo the Greek character was used to describe the mouth of Nile by Herodotus nearly 2500 years ago

A modern definition cites delta as ldquothe sub aerial and submerged contiguous sediment mass deposited in a body of water(ocean or lake) primarily by the action of a riverrdquo(Moore and Asquith1971p2563)

Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate

Shape of Delta The shape of a delta is not always the triangle that

suggested the name to Herodotus Delta shape is influenced by

a) Sediment input

b) Wave energy

c) Tidal energy

Controls on delta environment

Factors affecting delta regime morphology and facies (Elliot 1978a)

Magnitude of fluvial discharge

Delta morphology and sedimentary facies

Delta regime

Magnitude of wave and tidal currents

Climate tectonics subsidence sediment supply topography

Subenvironments of Delta Deltas are influenced by a complex combination

of fluvial and marine processes Each delta has more than a dozen distinct

environments of deposition These environments can be grouped into three

broad divisions

1 The delta plain with the meandering flood plains Swamps and beach complex

2 The steeper delta front

3 The broadly sloping prodelta which grades into the open shelf

Variations in delta morphology

The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics

Two main factors are the most important in determining the morphology of deltas

1) Effect of grain size

2) Depth of water in delta are going to deposit

(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits

(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands

(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies

(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water

Processes in a model delta Reduced to its simplest elements a delta forms

due to ldquounique hydrodynamic interactionrdquo between river water and seawater

There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater

Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth

Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Introduction To discuss deltas we should have great understanding

of depositional environment Depositional Environments Geomorphic setting in which a particular set of physical

chemical and biological processes operates to generate a certain kind of sedimentary deposit

Physical environment has ldquostaticrdquo and dynamic elements

1048708 Static basin geometry sediment composition water depth etc

1048708 Dynamic currents (wind water) precipitation climate

Chemical elements pH Eh salinity pCO2 etc Biological aspects activities of organisms (burrowing

skeletal particles etc) and their remains (eg peat)

Classification of Depositional Environments

Nonmarine Environments Colluvial and Alluvial fans Fluvial environments Lacustrine environments Aeolian environments

Costal(marginal marine) Environments River mouth environments Regressive river mouthsDeltas Transgressive river mouthsEstuaries Open shoreline(beach) environments Foreshore backshore

Marine Environments Shallow marine environments Shoreface Inner and outer shelf Deep marine environments Continental slope Abyssal plain(basin floor)

Depositional Environments1048708 Objective Use sedimentary deposits to

interpret depositional environments

1048708 Physical biological chemical parameters of

an environment combine to produce a body

of sediment characterized by specific

textural structural and compositional properties

1048708 Distinctive bodies of sediments or

sedimentary rocks are facies

What happenshellip What we wanthellip

Marginal marine environment

The marginal-marine(transitional) setting lies along the boundary between the continental and the marine depositional realms

It is a narrow zone dominated by Riverine Wave Tidal processes Salinities may range in different parts of the

system from fresh water through brackish water to supersaline depending upon the river discharge and climatic conditions

Deltaic system

The term ldquodeltardquo the Greek character was used to describe the mouth of Nile by Herodotus nearly 2500 years ago

A modern definition cites delta as ldquothe sub aerial and submerged contiguous sediment mass deposited in a body of water(ocean or lake) primarily by the action of a riverrdquo(Moore and Asquith1971p2563)

Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate

Shape of Delta The shape of a delta is not always the triangle that

suggested the name to Herodotus Delta shape is influenced by

a) Sediment input

b) Wave energy

c) Tidal energy

Controls on delta environment

Factors affecting delta regime morphology and facies (Elliot 1978a)

Magnitude of fluvial discharge

Delta morphology and sedimentary facies

Delta regime

Magnitude of wave and tidal currents

Climate tectonics subsidence sediment supply topography

Subenvironments of Delta Deltas are influenced by a complex combination

of fluvial and marine processes Each delta has more than a dozen distinct

environments of deposition These environments can be grouped into three

broad divisions

1 The delta plain with the meandering flood plains Swamps and beach complex

2 The steeper delta front

3 The broadly sloping prodelta which grades into the open shelf

Variations in delta morphology

The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics

Two main factors are the most important in determining the morphology of deltas

1) Effect of grain size

2) Depth of water in delta are going to deposit

(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits

(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands

(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies

(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water

Processes in a model delta Reduced to its simplest elements a delta forms

due to ldquounique hydrodynamic interactionrdquo between river water and seawater

There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater

Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth

Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Chemical elements pH Eh salinity pCO2 etc Biological aspects activities of organisms (burrowing

skeletal particles etc) and their remains (eg peat)

Classification of Depositional Environments

Nonmarine Environments Colluvial and Alluvial fans Fluvial environments Lacustrine environments Aeolian environments

Costal(marginal marine) Environments River mouth environments Regressive river mouthsDeltas Transgressive river mouthsEstuaries Open shoreline(beach) environments Foreshore backshore

Marine Environments Shallow marine environments Shoreface Inner and outer shelf Deep marine environments Continental slope Abyssal plain(basin floor)

Depositional Environments1048708 Objective Use sedimentary deposits to

interpret depositional environments

1048708 Physical biological chemical parameters of

an environment combine to produce a body

of sediment characterized by specific

textural structural and compositional properties

1048708 Distinctive bodies of sediments or

sedimentary rocks are facies

What happenshellip What we wanthellip

Marginal marine environment

The marginal-marine(transitional) setting lies along the boundary between the continental and the marine depositional realms

It is a narrow zone dominated by Riverine Wave Tidal processes Salinities may range in different parts of the

system from fresh water through brackish water to supersaline depending upon the river discharge and climatic conditions

Deltaic system

The term ldquodeltardquo the Greek character was used to describe the mouth of Nile by Herodotus nearly 2500 years ago

A modern definition cites delta as ldquothe sub aerial and submerged contiguous sediment mass deposited in a body of water(ocean or lake) primarily by the action of a riverrdquo(Moore and Asquith1971p2563)

Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate

Shape of Delta The shape of a delta is not always the triangle that

suggested the name to Herodotus Delta shape is influenced by

a) Sediment input

b) Wave energy

c) Tidal energy

Controls on delta environment

Factors affecting delta regime morphology and facies (Elliot 1978a)

Magnitude of fluvial discharge

Delta morphology and sedimentary facies

Delta regime

Magnitude of wave and tidal currents

Climate tectonics subsidence sediment supply topography

Subenvironments of Delta Deltas are influenced by a complex combination

of fluvial and marine processes Each delta has more than a dozen distinct

environments of deposition These environments can be grouped into three

broad divisions

1 The delta plain with the meandering flood plains Swamps and beach complex

2 The steeper delta front

3 The broadly sloping prodelta which grades into the open shelf

Variations in delta morphology

The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics

Two main factors are the most important in determining the morphology of deltas

1) Effect of grain size

2) Depth of water in delta are going to deposit

(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits

(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands

(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies

(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water

Processes in a model delta Reduced to its simplest elements a delta forms

due to ldquounique hydrodynamic interactionrdquo between river water and seawater

There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater

Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth

Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Classification of Depositional Environments

Nonmarine Environments Colluvial and Alluvial fans Fluvial environments Lacustrine environments Aeolian environments

Costal(marginal marine) Environments River mouth environments Regressive river mouthsDeltas Transgressive river mouthsEstuaries Open shoreline(beach) environments Foreshore backshore

Marine Environments Shallow marine environments Shoreface Inner and outer shelf Deep marine environments Continental slope Abyssal plain(basin floor)

Depositional Environments1048708 Objective Use sedimentary deposits to

interpret depositional environments

1048708 Physical biological chemical parameters of

an environment combine to produce a body

of sediment characterized by specific

textural structural and compositional properties

1048708 Distinctive bodies of sediments or

sedimentary rocks are facies

What happenshellip What we wanthellip

Marginal marine environment

The marginal-marine(transitional) setting lies along the boundary between the continental and the marine depositional realms

It is a narrow zone dominated by Riverine Wave Tidal processes Salinities may range in different parts of the

system from fresh water through brackish water to supersaline depending upon the river discharge and climatic conditions

Deltaic system

The term ldquodeltardquo the Greek character was used to describe the mouth of Nile by Herodotus nearly 2500 years ago

A modern definition cites delta as ldquothe sub aerial and submerged contiguous sediment mass deposited in a body of water(ocean or lake) primarily by the action of a riverrdquo(Moore and Asquith1971p2563)

Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate

Shape of Delta The shape of a delta is not always the triangle that

suggested the name to Herodotus Delta shape is influenced by

a) Sediment input

b) Wave energy

c) Tidal energy

Controls on delta environment

Factors affecting delta regime morphology and facies (Elliot 1978a)

Magnitude of fluvial discharge

Delta morphology and sedimentary facies

Delta regime

Magnitude of wave and tidal currents

Climate tectonics subsidence sediment supply topography

Subenvironments of Delta Deltas are influenced by a complex combination

of fluvial and marine processes Each delta has more than a dozen distinct

environments of deposition These environments can be grouped into three

broad divisions

1 The delta plain with the meandering flood plains Swamps and beach complex

2 The steeper delta front

3 The broadly sloping prodelta which grades into the open shelf

Variations in delta morphology

The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics

Two main factors are the most important in determining the morphology of deltas

1) Effect of grain size

2) Depth of water in delta are going to deposit

(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits

(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands

(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies

(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water

Processes in a model delta Reduced to its simplest elements a delta forms

due to ldquounique hydrodynamic interactionrdquo between river water and seawater

There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater

Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth

Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Depositional Environments1048708 Objective Use sedimentary deposits to

interpret depositional environments

1048708 Physical biological chemical parameters of

an environment combine to produce a body

of sediment characterized by specific

textural structural and compositional properties

1048708 Distinctive bodies of sediments or

sedimentary rocks are facies

What happenshellip What we wanthellip

Marginal marine environment

The marginal-marine(transitional) setting lies along the boundary between the continental and the marine depositional realms

It is a narrow zone dominated by Riverine Wave Tidal processes Salinities may range in different parts of the

system from fresh water through brackish water to supersaline depending upon the river discharge and climatic conditions

Deltaic system

The term ldquodeltardquo the Greek character was used to describe the mouth of Nile by Herodotus nearly 2500 years ago

A modern definition cites delta as ldquothe sub aerial and submerged contiguous sediment mass deposited in a body of water(ocean or lake) primarily by the action of a riverrdquo(Moore and Asquith1971p2563)

Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate

Shape of Delta The shape of a delta is not always the triangle that

suggested the name to Herodotus Delta shape is influenced by

a) Sediment input

b) Wave energy

c) Tidal energy

Controls on delta environment

Factors affecting delta regime morphology and facies (Elliot 1978a)

Magnitude of fluvial discharge

Delta morphology and sedimentary facies

Delta regime

Magnitude of wave and tidal currents

Climate tectonics subsidence sediment supply topography

Subenvironments of Delta Deltas are influenced by a complex combination

of fluvial and marine processes Each delta has more than a dozen distinct

environments of deposition These environments can be grouped into three

broad divisions

1 The delta plain with the meandering flood plains Swamps and beach complex

2 The steeper delta front

3 The broadly sloping prodelta which grades into the open shelf

Variations in delta morphology

The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics

Two main factors are the most important in determining the morphology of deltas

1) Effect of grain size

2) Depth of water in delta are going to deposit

(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits

(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands

(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies

(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water

Processes in a model delta Reduced to its simplest elements a delta forms

due to ldquounique hydrodynamic interactionrdquo between river water and seawater

There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater

Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth

Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

What happenshellip What we wanthellip

Marginal marine environment

The marginal-marine(transitional) setting lies along the boundary between the continental and the marine depositional realms

It is a narrow zone dominated by Riverine Wave Tidal processes Salinities may range in different parts of the

system from fresh water through brackish water to supersaline depending upon the river discharge and climatic conditions

Deltaic system

The term ldquodeltardquo the Greek character was used to describe the mouth of Nile by Herodotus nearly 2500 years ago

A modern definition cites delta as ldquothe sub aerial and submerged contiguous sediment mass deposited in a body of water(ocean or lake) primarily by the action of a riverrdquo(Moore and Asquith1971p2563)

Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate

Shape of Delta The shape of a delta is not always the triangle that

suggested the name to Herodotus Delta shape is influenced by

a) Sediment input

b) Wave energy

c) Tidal energy

Controls on delta environment

Factors affecting delta regime morphology and facies (Elliot 1978a)

Magnitude of fluvial discharge

Delta morphology and sedimentary facies

Delta regime

Magnitude of wave and tidal currents

Climate tectonics subsidence sediment supply topography

Subenvironments of Delta Deltas are influenced by a complex combination

of fluvial and marine processes Each delta has more than a dozen distinct

environments of deposition These environments can be grouped into three

broad divisions

1 The delta plain with the meandering flood plains Swamps and beach complex

2 The steeper delta front

3 The broadly sloping prodelta which grades into the open shelf

Variations in delta morphology

The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics

Two main factors are the most important in determining the morphology of deltas

1) Effect of grain size

2) Depth of water in delta are going to deposit

(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits

(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands

(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies

(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water

Processes in a model delta Reduced to its simplest elements a delta forms

due to ldquounique hydrodynamic interactionrdquo between river water and seawater

There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater

Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth

Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Marginal marine environment

The marginal-marine(transitional) setting lies along the boundary between the continental and the marine depositional realms

It is a narrow zone dominated by Riverine Wave Tidal processes Salinities may range in different parts of the

system from fresh water through brackish water to supersaline depending upon the river discharge and climatic conditions

Deltaic system

The term ldquodeltardquo the Greek character was used to describe the mouth of Nile by Herodotus nearly 2500 years ago

A modern definition cites delta as ldquothe sub aerial and submerged contiguous sediment mass deposited in a body of water(ocean or lake) primarily by the action of a riverrdquo(Moore and Asquith1971p2563)

Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate

Shape of Delta The shape of a delta is not always the triangle that

suggested the name to Herodotus Delta shape is influenced by

a) Sediment input

b) Wave energy

c) Tidal energy

Controls on delta environment

Factors affecting delta regime morphology and facies (Elliot 1978a)

Magnitude of fluvial discharge

Delta morphology and sedimentary facies

Delta regime

Magnitude of wave and tidal currents

Climate tectonics subsidence sediment supply topography

Subenvironments of Delta Deltas are influenced by a complex combination

of fluvial and marine processes Each delta has more than a dozen distinct

environments of deposition These environments can be grouped into three

broad divisions

1 The delta plain with the meandering flood plains Swamps and beach complex

2 The steeper delta front

3 The broadly sloping prodelta which grades into the open shelf

Variations in delta morphology

The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics

Two main factors are the most important in determining the morphology of deltas

1) Effect of grain size

2) Depth of water in delta are going to deposit

(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits

(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands

(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies

(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water

Processes in a model delta Reduced to its simplest elements a delta forms

due to ldquounique hydrodynamic interactionrdquo between river water and seawater

There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater

Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth

Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Deltaic system

The term ldquodeltardquo the Greek character was used to describe the mouth of Nile by Herodotus nearly 2500 years ago

A modern definition cites delta as ldquothe sub aerial and submerged contiguous sediment mass deposited in a body of water(ocean or lake) primarily by the action of a riverrdquo(Moore and Asquith1971p2563)

Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate

Shape of Delta The shape of a delta is not always the triangle that

suggested the name to Herodotus Delta shape is influenced by

a) Sediment input

b) Wave energy

c) Tidal energy

Controls on delta environment

Factors affecting delta regime morphology and facies (Elliot 1978a)

Magnitude of fluvial discharge

Delta morphology and sedimentary facies

Delta regime

Magnitude of wave and tidal currents

Climate tectonics subsidence sediment supply topography

Subenvironments of Delta Deltas are influenced by a complex combination

of fluvial and marine processes Each delta has more than a dozen distinct

environments of deposition These environments can be grouped into three

broad divisions

1 The delta plain with the meandering flood plains Swamps and beach complex

2 The steeper delta front

3 The broadly sloping prodelta which grades into the open shelf

Variations in delta morphology

The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics

Two main factors are the most important in determining the morphology of deltas

1) Effect of grain size

2) Depth of water in delta are going to deposit

(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits

(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands

(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies

(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water

Processes in a model delta Reduced to its simplest elements a delta forms

due to ldquounique hydrodynamic interactionrdquo between river water and seawater

There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater

Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth

Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate

Shape of Delta The shape of a delta is not always the triangle that

suggested the name to Herodotus Delta shape is influenced by

a) Sediment input

b) Wave energy

c) Tidal energy

Controls on delta environment

Factors affecting delta regime morphology and facies (Elliot 1978a)

Magnitude of fluvial discharge

Delta morphology and sedimentary facies

Delta regime

Magnitude of wave and tidal currents

Climate tectonics subsidence sediment supply topography

Subenvironments of Delta Deltas are influenced by a complex combination

of fluvial and marine processes Each delta has more than a dozen distinct

environments of deposition These environments can be grouped into three

broad divisions

1 The delta plain with the meandering flood plains Swamps and beach complex

2 The steeper delta front

3 The broadly sloping prodelta which grades into the open shelf

Variations in delta morphology

The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics

Two main factors are the most important in determining the morphology of deltas

1) Effect of grain size

2) Depth of water in delta are going to deposit

(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits

(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands

(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies

(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water

Processes in a model delta Reduced to its simplest elements a delta forms

due to ldquounique hydrodynamic interactionrdquo between river water and seawater

There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater

Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth

Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Controls on delta environment

Factors affecting delta regime morphology and facies (Elliot 1978a)

Magnitude of fluvial discharge

Delta morphology and sedimentary facies

Delta regime

Magnitude of wave and tidal currents

Climate tectonics subsidence sediment supply topography

Subenvironments of Delta Deltas are influenced by a complex combination

of fluvial and marine processes Each delta has more than a dozen distinct

environments of deposition These environments can be grouped into three

broad divisions

1 The delta plain with the meandering flood plains Swamps and beach complex

2 The steeper delta front

3 The broadly sloping prodelta which grades into the open shelf

Variations in delta morphology

The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics

Two main factors are the most important in determining the morphology of deltas

1) Effect of grain size

2) Depth of water in delta are going to deposit

(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits

(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands

(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies

(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water

Processes in a model delta Reduced to its simplest elements a delta forms

due to ldquounique hydrodynamic interactionrdquo between river water and seawater

There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater

Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth

Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Subenvironments of Delta Deltas are influenced by a complex combination

of fluvial and marine processes Each delta has more than a dozen distinct

environments of deposition These environments can be grouped into three

broad divisions

1 The delta plain with the meandering flood plains Swamps and beach complex

2 The steeper delta front

3 The broadly sloping prodelta which grades into the open shelf

Variations in delta morphology

The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics

Two main factors are the most important in determining the morphology of deltas

1) Effect of grain size

2) Depth of water in delta are going to deposit

(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits

(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands

(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies

(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water

Processes in a model delta Reduced to its simplest elements a delta forms

due to ldquounique hydrodynamic interactionrdquo between river water and seawater

There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater

Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth

Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Variations in delta morphology

The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics

Two main factors are the most important in determining the morphology of deltas

1) Effect of grain size

2) Depth of water in delta are going to deposit

(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits

(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands

(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies

(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water

Processes in a model delta Reduced to its simplest elements a delta forms

due to ldquounique hydrodynamic interactionrdquo between river water and seawater

There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater

Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth

Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits

(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands

(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies

(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water

Processes in a model delta Reduced to its simplest elements a delta forms

due to ldquounique hydrodynamic interactionrdquo between river water and seawater

There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater

Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth

Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands

(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies

(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water

Processes in a model delta Reduced to its simplest elements a delta forms

due to ldquounique hydrodynamic interactionrdquo between river water and seawater

There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater

Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth

Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies

(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water

Processes in a model delta Reduced to its simplest elements a delta forms

due to ldquounique hydrodynamic interactionrdquo between river water and seawater

There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater

Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth

Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water

Processes in a model delta Reduced to its simplest elements a delta forms

due to ldquounique hydrodynamic interactionrdquo between river water and seawater

There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater

Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth

Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Processes in a model delta Reduced to its simplest elements a delta forms

due to ldquounique hydrodynamic interactionrdquo between river water and seawater

There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater

Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth

Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Levees Ridges on either side of the distributary channels

are termed ldquoleveesrdquo The sand carried in the stream is deposited along

the sides of the jet in the subaqueous levees where friction and mixing slow the flow

Distributary channels It is channel that branches off and flow away from

a main channel or stream Common feature of delta

Distributary channel sands are abundantly

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

I Cross-bedded with plenty of ripple cross-lamination

II Scour-and-fill structures

III Discontinuous clay lenses

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Distributary mouth bars Further offshore where friction and spreading

begins to slow the jet sediments is dropped in the distributary mouth bars

The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them

Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars

Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface

nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees

Delta slopefront The delta platform grades away from the source

into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Pro-delta Delta slope in turn passes down into the delta slope

on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs

Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Classification of delta Deltas can be classified in several ways

(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists

Deltas are classified thus as

1) Fluvial-dominated delta

2) Tide-dominated delta

3) Wave-dominated delta

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Fluvial-dominated delta A fluvial or river dominated delta has a large

volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large

If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small

It occur where the tidal range is very low and the tidal current action is very weak

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

ExampleMississippi delta It is created when very large amounts of sediment

are carried into relatively quiet water Partly because dredging has kept the major

distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea

The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Stream-dominated delta

Aster satellite photo of the Mississippi River delta taken in 2001

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Tide-dominated delta A tide dominated delta has many linear channels

parallel to the tidal flow and perpendicular to the shore

It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution

These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Example

The Ganges-Brahmaputra

Delta in Bangladesh is a good example of a tide-dominated delta

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Wave-dominated delta A wave dominated delta is smoothly arcuate the

wave action reworks the sediments and make such deltas much sandier than other types of deltas

It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal

this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

ExampleThe Nile Delta

It is a wave-dominated delta that contains barrier islands along its ocean-ward side

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

mixed-process deltas The examples discussed above illustrate some

differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related

Many deltas have characteristics that are transitional between these end members types

Example The Copper River delta in the Gulf of Alaska

provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

The Copper River Delta Gulf of Alaska

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

General delta patterns A well-developed delta provides the whole gamut

of clastic sediment types from carbonaceous mudstones to conglomerates

The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns

I High-destructive deltas

II High-constructive deltas of birdfoot type

III High-constructive deltas of lobate type

IV Fan deltas

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Typical sequence

The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands

This is opposite to the fining upward sequence found in most meandering fluvial system

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Why deltas are so important Ancient deltaic deposits are extremely important

economically Due to variety of environments in the deltas it

makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary

deposits associated with deltas Located near the boundaries between marine

deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

They hosts most of the worldrsquos coal and many major petroleum provinces

The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)

Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels

Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Sedimentary structures and fossils

Numerous types of sedimentary structures such as

1 Cross bedding

2 Ripple marks

3 Bioturbation structures

4 Slump structure and

5 Mud diapirs occur in deltaic deposits

A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Structural features in deltaic reservoir

Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures

Structural features can broadly divided into two classes based on the timing of the deformation

Syndepositional deformation features Syndepositional deformational processes which

includes

a Slumping

b Mud diapirism

c Growth faulting are common in lower delta plain environments and operate during delta formation

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Post-depositional deformation Post-depositional deformational features includes

a Folding

b Tilting faulting fracturing This is due to tectonic forces and consequent

movement of earthrsquos crust

Significances Structural features can modify the sandstone body

geometry These features are important in the migration

accumulation and trapping of petroleum

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Migration of hydrocarbons from the source rock enhanced by

Faulting and Fracturing These accumulation or trapping of oil is caused by

permeability barriers which prevent further migration of the petroleum

When the permeability barriers is a structural feature the reservoir is considered structural traps

Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Examples in Pakistan

Samber Formation is source rock of deltaic environment

Goru Formation is a reservoir rock of deltaic environment

Its upper part acts as a seal rock

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You

Thank You

• DELTAS
• Contents
• Introduction
• Slide 4
• Classification of Depositional Environments
• Slide 6
• Depositional Environments
• Slide 8
• Marginal marine environment
• Deltaic system
• Slide 11
• Controls on delta environment
• Subenvironments of Delta
• Slide 14
• Variations in delta morphology
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Processes in a model delta
• Slide 21
• Levees
• Slide 23
• Distributary mouth bars
• Morphological units of deltas
• Pro-delta
• Classification of delta
• Slide 28
• Fluvial-dominated delta
• Example
• Slide 31
• Tide-dominated delta
• Example (2)
• Wave-dominated delta
• Example (3)
• mixed-process deltas
• Slide 37
• General delta patterns
• Slide 39
• Typical sequence
• Why deltas are so important
• Slide 42
• Sedimentary structures and fossils
• Structural features in deltaic reservoir
• Post-depositional deformation
• Slide 46
• Examples in Pakistan
• Thank You