G 1 Geology of Petroleum Systems

7/22/2019 G 1 Geology of Petroleum Systems

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Geology ofPetroleum Systems


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Petroleum Geology

Objectives are to be able to:

Discuss basic elements of Petroleum Systems Describe plate tectonics and sedimentary basins

Recognize names of major sedimentary rock types Describe importance of sedimentary environmentsto petroleum industry

Describe the origin of petroleum

Identify hydrocarbon trap types Define and describe the important geologic

controls on reservoir properties, porosity and

permeability


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Outline

Petroleum Systems approach Geologic Principles and geologic time Rock and minerals, rock cycle, reservoir

properties Hydrocarbon origin, migration and

accumulation

Sedimentary environments and facies;stratigraphic traps

Plate tectonics, basin development, structuralgeology

Structural traps


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Petroleum System - A Definition

A Petroleum System is a dynamic hydrocarbonsystem that functions in a restricted geologic

space and time scale.

A Petroleum System requires timely

convergence of geologic events essential tothe formation of petroleum deposits.

These Include:

Mature source rock

Hydrocarbon expulsionHydrocarbon migrationHydrocarbon accumulationHydrocarbon retention

(modified from Demaison and Huizinga, 1994)


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In order to have a commercial hydrocarbon

prospect, several requirement must be met.There must be

(1) a hydrocarbon source,

(2) a reservoir rock, and

(3) a trap

Moreover, the relative time at which these

features developed is important.

The systematic assessment of these parameterand their affect on hydrocarbon occurrence is

known as aPetroleum Systems approach to oil

and gas evaluation.

Petroleum Systems


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Cross Section Of A Petroleum System

Overburden Rock

Seal Rock

Reservoir Rock

Source Rock

Underburden Rock

Basement Rock

Top Oil Window

Top Gas Window

Geographic Extent of Petroleum System

Petroleum Reservoir (O)

Fold-and-Thrust Belt

(arrows indicate relative fault motion)

Essential

Elements

of

Petroleum

System

(Foreland Basin Example)

(modified from Magoon and Dow, 1994)

O O

Sed

imentary

BasinFill

O

Stratigraphic

Extent ofPetroleum

System

Pod of Active

Source Rock

Extent of Prospect/FieldExtent of Play


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This cross section shows the elements of a PetroleumSystem.

Potential reservoir sandstones (yellow), deposited at thebasin margin, intertongue to the left with organic-rich sourcerocks.

Owing to the increasing temperature with depth, the sourcerocks are mature for gas in the deep basin.

Below the oil window, the source rocks are generating oil. Hydrocarbons migrate up the flank of the basin and

accumulate in a trap (structural).

The layer overlying the reservoir is a low-permeability seal. Inorder to have a commercial field/ prospect, the trap mustform prior to hydrocarbon migration, and the trap must have

maintained its integrity.


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Basic Geologic Principles

Uniformitarianism Original Horizontality

Superposition Cross-Cutting Relationships


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The following are basic principles or laws are used to evaluate the

relative ages and the relations among rock layers.

Uniformitarianism -The present is the key to the past. Bystudying modern geologic processes, we can interpret pastgeologic events and rock-forming processes.

Original Horizonality- Sedimentary layers are deposited ina horizontal or nearly horizontal position. If sedimentary

layers are tilted or folded, they have been subjected todeforming stresses.

Superposition- Younger sedimentary beds occur on top ofolder beds, unless they have been overturned or faulted.

Cross-Cutting Relations- Any geologic feature that cutsanother geologic feature is younger than the feature that it

cuts.


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Cross-Cutting Relationships

Angular Unconformity

A

B

C

D

E

F

G

HIJ

K

IgneousDike


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Law of cross-cutting relationships.

In the figure above, the igneous dike (F) is younger

than layers A-E but older than layer G, because ageologic feature is younger than any other geologic

feature that it cuts.

This is an important law for determining the relativeages of geologic features.

According to the Law of Superposition,layer I is

older than layer J, and the rocks beneath the

unconformity are older from left to right.

From the Principle of Original Horizonality, we

infer that layers A through F have been

deformed.


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Disconformity An unconformity in which the beds above and below

are parallel

Angular Unconformity An unconformity in which the older bed intersect the

younger beds at an angle

Nonconformity An unconformity in which younger sedimentaryrocks overlie older metamorphic or intrusive

igneous rocks

Types of Unconformities


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Sedimentary rock are deposited in successivelayers that record the history of their time,

much like the pages in history book. However, the rock record is never complete. Missing layers (gaps in time) result in

unconformities. An unconformity is a surface of non-deposition

or erosion that separates younger rocks from

older rocks. The previous slide shows an angular

unconformity.


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Correlation

Establishes the age equivalence of rocklayers in different areas

Methods: Similar lithology

Similar stratigraphic section

Index fossils

Fossil assemblages Radioactive age dating


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0

50

100

150

200

250

300

350

400

450

500

550

600

0

10

20

30

40

50

60

Cry

ptozoic

(Prec

ambrian)

Phanerozoic

Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Permian

Pennsylvanian

Mississippian

Devonian

Silurian

Ordovician

Cambrian

Millions

ofyearsago

Million

sofyearsago

Billion

sofyearsago

0

1

2

3

4

4.6

Paleocene

Eocene

Oligocene

Miocene

Pliocene

Pleistocene

Recent

Quaternary

pe

riod

Tertiary

period

Eon Era Period Epoch

Geologic Time Chart

Pale

ozoic

Mesozoic

C

enozoicEra

Initially, the geologic time scale was

developed on the basis of relativegeologic ages, using fossil assemblages

and the laws of superposition, cross-

cutting relations, etc. Subsequently,

absolute ages were assigned to the timescale on the basis of radioactive dating.


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Rocks


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Classification of Rocks

SEDIMENTARY

Rock-forming

process

Sourceof

material

IGNEOUS METAMORPHIC

Molten materials in

deep crust and

upper mantle

Crystallization

(Solidification of melt)

Weathering and

erosion of rocks

exposed at surface

Sedimentation, burial

and lithification

Rocks under high

temperatures

and pressures in

deep crust

Recrystallization due to

heat, pressure, or

chemically active fluids


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The Rock Cycle

Magma

Metamorphic

Rock

SedimentaryRock

Igneous

Rock

Sediment

Heat and Pressure

Weathering,Transportationand Deposition

a

n

i


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Siltstone, mudand shale

~75%

Sedimentary Rock Types

Relative abundanceSandstone

and conglomerate

~11%

Limestone and

dolomite

~13%


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Quartz Crystals

Naturally OccurringSolid

Generally Formed byInorganic Processes

Ordered InternalArrangement of Atoms(Crystal Structure)

Chemical Compositionand Physical PropertiesFixed or Vary WithinA Definite Range

Minerals - Definition


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Average Detrital Mineral

Composition of Shale and Sandstone

Mineral Composition Shale (%) Sandstone (%)

Clay Minerals

Quartz

Feldspar

Rock Fragments

Carbonate

Organic Matter,Hematite, andOther Minerals

60

30

4


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The Physical and Chemical Characteristics

of Minerals Strongly Influence theComposition of Sedimentary Rocks

Quartz

Feldspar

Calcite

Mechanically and Chemically Stable

Can Survive Transport and Burial

Nearly as Hard as Quartz, but

Cleavage Lessens Mechanical Stability

May be Chemically Unstable in Some

Climates and During Burial

Mechanically Unstable During Transport

Chemically Unstable in Humid Climates

Because of Low Hardness, Cleavage, and

Reactivity With Weak Acid


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Some Common Minerals

Silicates

Oxides Sulfides Carbonates Sulfates Halides

Non-Ferromagnesian(Common in Sedimentary Rocks)

Anhydr i teGypsum

HaliteSylvi te

Aragoni teCalciteDolomiteFe-DolomiteAnker i te

Pyr i teGalenaSphaler i te

Ferromagnesian(not common in sedimentary rocks)

HematiteMagnet i te

QuartzMuscovite (mica)Feldspars

Potassium feldspar (K-spar)OrthoclaseMicroc l ine, etc.

PlagioclaseAlbi te (Na-r ich - common) throughAno rth i te (Ca-r ich - not common)

OlivinePyroxene

AugiteAmphibole

HornblendeBiotite (mica)

Red = Sedimentary Ro ck-Forming Minerals


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The Four Major Components

Framework Sand (and Silt) Size Detrital Grains

Matrix Clay Size Detrital Material

Cement Material precipitated post-depositionally,

during burial. Cements fill pores and replaceframework grains

Pores

Voids between above components


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Norphlet Sandstone, Offshore Alabama, USA

Grains are About =< 0.25 mm in Diameter/Length

PRF KF

P

KF = PotassiumFeldspar

PRF = Plutonic RockFragment

P = Pore

Potassium Feldspar isStained Yellow With a

Chemical Dye

Pores are ImpregnatedWith Blue-Dyed Epoxy

CEMENT

Sandstone Composition

Framework Grains


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Scanning Electron Micrograph

Norphlet Formation, Offshore Alabama, USA

Pores Provide the

Volume to ContainHydrocarbon Fluids

Pore Throats Restrict

Fluid Flow

Pore

Throat

Porosity in Sandstone


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Secondary Electron Micrograph

Jurassic Norphlet SandstoneHatters Pond Field, Alabama, USA (Photograph by R.L. Kugler)

Illite

SignificantPermeabilityReduction

NegligiblePorosityReduction

Migration ofFines Problem

High IrreducibleWater Saturation

Clay Minerals in Sandstone Reservoirs

Fibrous Authigenic Illite


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Jurassic Norphlet Sandstone

Offshore Alabama, USA (Photograph by R.L. Kugler)

Occurs as ThinCoats on DetritalGrain Surfaces

Occurs in SeveralDeeply BuriedSandstones WithHigh ReservoirQuality

Iron-RichVarieties ReactWith Acid

~ 10 m


Authigenic Chlorite


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Carter SandstoneNorth Blowhorn Creek Oil Unit

Black Warrior Basin, Alabama, USA

Significant PermeabilityReduction

High Irreducible WaterSaturation

Migration of FinesProblem

(Photograph by R.L. Kugler)


Authigenic Kaolinite


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100

10

1

0.1

0.01 0.01

0.1

1

10

100

1000

2 6 10 14 2 6 10 14 18

Pe

rmeability(m

d)

Porosity (%)

Authigenic Illite Authigenic Chlorite

(modified from Kugler and McHugh, 1990)

Effects of Clays on Reservoir Quality

I fl f Cl Mi l


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Dispersed Clay

Clay Lamination

Structural Clay(Rock Fragments,

Rip-Up Clasts,Clay-Replaced Grains)

fe

fe

fe

ClayMinerals

Detrital QuartzGrains

Influence of Clay-Mineral

Distribution on Effective Porosity


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Diagenesis

CarbonateCemented

OilStained

Diagenesis is the Post-Depositional Chemical andMechanical Changes thatOccur in Sedimentary Rocks

Some Diagenetic Effects IncludeCompactionPrecipitation of CementDissolution of Framework

Grains and Cement

The Effects of Diagenesis MayEnhance or Degrade ReservoirQuality

Whole Core

Misoa Formation, Venezuela


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Fluids Affecting Diagenesis

Precipitation

Subsidence

CH4,CO2,H2S

Petroleum

Fluids

Meteoric

Water

MeteoricWater

COMPACTIONAL

WATER

EvapotranspirationEvaporation

Infiltration

Water Table

Zone of abnormal pressure

Isotherms

(modified from from Galloway and Hobday, 1983)


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Thin Section Micrograph - Plane Polarized Light

Avile Sandstone, Neuquen Basin, Argentina

Dissolution of

Framework Grains

(Feldspar, for

Example) and

Cement may

Enhance the

Interconnected

Pore System

This is CalledSecondary Porosity

Pore

Quartz Detrital

Grain

Partially

Dissolved

Feldspar

(Photomicrograph by R.L. Kugler)

Dissolution Porosity


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Hydrocarbon Generation,

Migration, and Accumulation


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Organic Matter in Sedimentary Rocks

Reflected-Light Micrograph

of Coal

Vitrinite

Kerogen

Disseminated Organic Matter inSedimentary Rocks That is Insolublein Oxidizing Acids, Bases, andOrganic Solvents.

VitriniteA nonfluorescent type of organic materialin petroleum source rocks derivedprimarily from woody material.

The reflectivity of vitrinite is one of the

best indicators of coal rank and thermalmaturity of petroleum source rock.


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Interpretation of Total Organic Carbon (TOC)

(based on early oil window maturity)HydrocarbonGenerationPotential

TOC in Shale(wt. %)

TOC in Carbonates(wt. %)

Poor

Fair

Good

Very Good

Excellent

0.0-0.5

0.5-1.0

1.0-2.0

2.0-5.0

>5.0

0.0-0.2

0.2-0.5

0.5-1.0

1.0-2.0

>2.0


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Schematic Representation of the Mechanism

of Petroleum Generation and Destruction

(modified from Tissot and Welte, 1984)

Organic Debris

Kerogen

Carbon

Initial Bitumen

Oil and Gas

Methane

Oil Reservoir

MigrationThermal Degradation

Cracking

Diagenesis

Catagenesis

MetagenesisProgre

ssiveBurialan

dHeating


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Incipient Oil Generation

Max. Oil Generated

Oil Floor

Wet Gas Floor

Dry Gas Floor

Max. Dry GasGenerated

(modified from Foster and Beaumont, 1991, after Dow and OConner, 1982)

VitriniteReflectance(Ro

)%

Weight%

CarboninKero

gen

SporeColo

rationIndex(S

CI)

Pyr

olysisT

(C)

max

0.2

0.3

0.40.5

4.0

3.0

2.0

1.3

1

2

3

4

56

789

10

430

450

465

65

70

75

80

85

90

95

0.60.70.80.91.01.2

OIL

WetGas

DryGas

Comparison of Several Commonly Used

Maturity Techniques and Their Correlation

to Oil and Gas Generation Limits


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Reservoirrock

Seal

Migration route

Oil/watercontact (OWC)

Hydrocarbonaccumulation

in thereservoir rock

Top of maturity

Source rock

Fault(impermeable)

Generation, Migration, and

Trapping of Hydrocarbons

C S ti Of A P t l S t


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Cross Section Of A Petroleum System

Overburden Rock

Seal Rock

Reservoir Rock

Source Rock

Underburden Rock

Basement Rock

Top Oil Window

Top Gas Window

Geographic Extent of Petroleum System

Petroleum Reservoir (O)

Fold-and-Thrust Belt

(arrows indicate relative fault motion)

Essential

Elements

of

Petroleum

System

(Foreland Basin Example)

(modified from Magoon and Dow, 1994)

O O

Sedimentary

B

asinFill

O

Stratigraphic

Extent ofPetroleum

System

Pod of Active

Source Rock

Extent of Prospect/FieldExtent of Play


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Hydrocarbon Traps

Structural traps

Stratigraphic traps

Combination traps

Structural Hydrocarbon Traps


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Structural Hydrocarbon Traps

Salt

Diapir

Oil/Water

Contact

GasOil/Gas

Contact

Oil

ClosureOilShale Trap

Fracture Basement

(modified from Bjorlykke, 1989)

Fold Trap

Oil

Salt

Dome


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Anticlinal Theory

Gas

Oil

Water

Petroleum Accumulates in Structural Closure

Tar sand near Redden Oklahoma (Atoka County)


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Oil

Sandstone Shale

Hydrocarbon Traps - Dome

Gas


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Fault Trap

Oil / Gas

Stratigraphic Hydrocarbon Traps


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Oil/Gas

Oil/Gas

Oil/Gas

Stratigraphic Hydrocarbon Traps

Uncomformity

Channel Pinch Out


Unconformity Pinch out


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AsphaltTrap

Water

Meteoric

Water

Biodegraded

Oil/Asphalt

Partly

Biodegraded Oil

Hydrodynamic Trap

Shale

Oil

Water

Hydrostatic

Head


Other Traps


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Heterogeneity


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Reservoir Heterogeneity in Sandstone

Heterogeneity May

Result From:

Depositional Features

Diagenetic Features

(Whole Core Photograph, Misoa

Sandstone, Venezuela)

Heterogeneity

Segments Reservoirs

Increases Tortuosity of

Fluid Flow


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Reservoir Heterogeneity in Sandstone

Heterogeneity Also May

Result From:

Faults

Fractures

Faults and Fractures may

be Open (Conduits) or

Closed (Barriers) to Fluid

Flow

(Whole Core Photograph, Misoa

Sandstone, Venezuela)


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Bounding

Surface

Bounding

Surface

Eolian Sandstone, Entrada Formation, Utah, USA

Geologic Reservoir Heterogeneity


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Scales of Investigation Used inReservoir Characterization

Gigascopic

Megascopic

Macroscopic

Microscopic

Well Test

Reservoir ModelGrid Cell

Wireline LogInterval

Core Plug

GeologicalThin Section

Relative Volume

1

1014

2 x 1012

3 x 107

5 x 102

300 m

50 m

300 m

5 m 150 m

2 m

1 m

cm

mm - m

(modified from Hurst, 1993)


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Stages In The Generation ofAn Integrated Geological Reservoir Model

Log AnalysisWell Test Analysis

Core Analysis

Regional GeologicFramework

DepositionalModel

DiageneticModel

IntegratedGeologic Model

Applications Studies

Model TestingAnd Revision

StructuralModel

FluidModel

(As Needed)

(As Needed)

Geologic Activities

Reserves EstimationSimulation

G 1 Geology of Petroleum Systems

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