Concepts of Petroleum Geology

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CONCEPTS OF

PETROLEUM GEOLOGY

AN INTRODUCTIONAN INTRODUCTION

OIL AND NATURAL GAS CORPORATION LTD.

21st TO 24th DECEMBER - 2009

SIBSAGAR

WORKSHOP ON

TECHNOLOGY IMPERATIVES

FOR EXPLORATION AND PRODUCTION

OF OIL & GAS


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PETROLEUM GEOLOGY REFERS TO THE SPECIFIC SET

OF GEOLOGICAL DISCIPLINES THAT ARE APPLIED TO

THE SEARCH FOR HYDROCARBONS DURING OILEXPLORATION

PETROLEUM GEOLOGY IS PRINCIPALLY CONCERNEDWITH THE EVALUATION OF SEVEN KEY ELEMENTS IN A

SEDIMENTARY BASIN TO OBTAIN AN IDEA OF THE

SUBSURFACE AND OVERALL PETROLEUM SYSTEM.

Source

Reservoir

Seal

Trap

Timing

Maturation and Migration


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1. EVALUATION OF THE SOURCE

This involves quantification and evaluation of the nature of

organic-rich rocks so that the type and quality of expelledhydrocarbon in a basin can be assessed by GEOCHEMICAL

methods of analysis.

STEPS IN SOURCE ROCK ANALYSIS First establish likelihood of presence of organic-rich sediments

deposited in the past on the basis of studies of local

stratigraphy, paleogeography and sedimentology of the area. Identification and delineation of area of potential source rock.

Determine the type of KEROGEN and state of its maturation.

Calculation of thermal maturity and timing of maturation. Finally determine the likelihood of oil / gas generation in the area

and calculate the depth of oil window.

(Majority of oil generation occurs in the 60 to 120C range.

Gas generation starts at similar temperatures, but maycontinue up beyond this range, perhaps as high as 200C.)


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GEOCHEMICAL LOG

Hydrogenyield % wt VroOrganic CarbonH Index H/C indications


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2.THE RESERVOIR

It is a porous and permeable lithological unit or set of

units that holds the hydrocarbon reserves. The commontypes include sandstone and limestone.

STEPS IN ANALYSIS OF RESERVOIRS

First determine the type of lithofacies of the reservoir.Assessment of their POROSITY (to calculate the volume of

in situ hydrocarbons) and PERMEABILITY (to calculate

how easily hydrocarbons will flow out of them). Study the Post depositional Diagenetic changes in reservoir.

Establish depositional environment and geometry of the

reservoirs.

Some of the key disciplines used in reservoir analysis are

stratigraphy, sedimentology, reservoir engineering and the

technique of Formation evaluation using wireline tools.

Siesmic attributes of subsurface rocks generatedthrough seismic data processing are used to infer

physical / sedimentary properties of the rocks.


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CC#21 CC#20

8 5 1 8 7 6 4

RESERVOIR ROCK


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RESERVOIR ROCKS


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3. THE SEAL OR CAP ROCK

It is a unit with low permeability that impedes the escape of

hydrocarbons from the reservoir rock.

Common seals include EVAPORITES, CHALKS and

SHALE.

Analysis of seals involves assessment of their thickness and

extent, such that their effectiveness can be quantified.

4. THE TRAP

It is the stratigraphic or structural feature that ensures the

juxtaposition of reservoir and seal such that hydrocarbonsremain trapped in the subsurface, rather than escaping

and being lost.

The common types are Structural, Stratigraphic andCombination Traps.


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A structural trap, where a fault has juxtaposed a porous andpermeable reservoir against an impermeable seal. Oil (shown

in red) accumulates against the seal, to the depth of the base

of the seal. Any further oil migrating in from the source will

escape to the surface and seep.

SURFACE OIL SEEP

Oil accumulation in trap

SOURCE KITCHEN

AREA


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TYPES OF TRAPS

STRUCTURAL TRAP: Here the trap has been produced by

deformation of the beds after they were deposited, either byfolding or faulting.

STRATIGRAPHIC TRAP: Here the trap is formed bychanges in the nature of the rocks themselves, or in their

layering, the only structural effect being a tilt to allow the oil

to migrate through the reservoir.

COMBINATION TRAPS: Here the trap is formed partly by

structural and partly by stratigraphic effects, but not entirely

due to either.

HYDRODYNAMIC TRAPS: These Traps is due to water

flowing through the reservoir and holding the oil in placeswhere it would not otherwise be trapped.


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COMMON TRAP TYPES

Structural Structural

Structural


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COMMON TRAP TYPES


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5.ANALYSIS OF MATURATIONIt involves assessing the thermal history of the source rock in

order to make predictions of the amount and timing of

hydrocarbon generation and expulsion.

6&7. THE TIME AND NATURE OF MIGRATIONFinally, the careful studies of reveal information on how

hydrocarbons move from source to reservoir and help

quantify the source (or kitchen) of hydrocarbons in aparticular area.


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Extreme Global Warminggave excessive Algal Growths

Organic debris

90 & 150

million years

ago

Rifts formed as

the Continentsmoved apart


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Chemical

reactionsconvertedorganic debrisinto oil when

buried & heated

Rifts filledby sedimentwashed in

from

borderlands

And then came the rains


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Generation Migration Entrapment

JMAJMA

24803

120 F120 F

350 F350 F

GenerationGeneration

MigrationMigration

Seal RockSeal Rock

ReservoirRockReservoirRock

OilOil

WaterWater

GasCapGasCap

EntrapmentEntrapmentAccumulationAccumulation

Source RockSource Rock

Critical

Temperature

60-120 0C

ORIGIN OF PETROLEUM FORMS


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Petroleum is derived from the remains of living things

which contains a material called kerogen. Before dead organic matter becomes petroleum with time,

the kerogen matures into an assortment of hydrocarbon

molecules of all sizes and weights.

The lightest (small) hydrocarbon molecules waft away as

natural gas, and the heavier ones make up an oily liquid.

Petroleum source rocks are of terrestrial and marine origin.

Terrestrial source rocks are deposited in lakes, delta andriver basins having woody plant matter, algae etc.

Marine source rocks contain dead planktons, algae,

organic remains etc. In both the settings, the mixture is buried under conditions

of no oxygen. The kerogen are classified as type I,II & III

as per their origin and are capable of producing oil or gasor both.

ORIGIN OF PETROLEUM FORMS


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Under the anaerobic conditions, the kerogen is transformed

into a flammable substance called bitumen by the action ofheat and anaerobic microbes in the sediment and natural

catalysts.

Most of the bitumen is eventually cooked into tarry asphalt

releasing hydrocarbon molecules (as well as water and

carbon dioxide) out of the source rock as it heats.

Heavy oils form first, then light oils. As temperatures rise to

and above 100 C, source rocks produce more gas.

Being lighter than rocks, petroleum tends to rise upwardthrough fractures and the pores of coarse sandstone beds.

A small fraction of that leakage, perhaps 2% is preserved in

large pools having an impermeable cap / seal over it.


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CHARACTERISTICS OF PETROLEUM RESERVOIRS

A reservoir is sponge-like rock with open space between

its grains -porosity. The porosity may be primary or it might be secondary as

groundwater dissolves pores in the rock or as minerals

undergo alteration or may have formed due to tectonic

activities.

One source of porosity is the transformation of calcite to

dolomite by fluids rich in magnesium, which takes up less

space. Besides porosity, there must be high permeability ie. the

connectedness of pores that allows fluid to move easily

through the reservoir rock. Permeability, porosity in combination with geologic

structure are all of interest to petroleum geologists as it

provides sites of hydrocarbon accumulation underfavourable conditions.


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BASIC POROSITY TYPES

POROSITY TYPES IN LIMESTONE


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POROSITY TYPES IN LIMESTONE

Matrix porosity

Moldic porosity

EXPLORATION CYCLE


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EXPLORATION CYCLE

IN A SEDIMENTARY BASIN

Geological Field Mapping / Remote sensing

Gravity Magnetic Surveys

Seismic Data API (2D/3D)

Prospect Identification

Drilling

Reservoir Studies

Production

Well Logs & VSP

BHS &

Simulation

EXPLORATION ACTIVITIES IN A SEDIMENTARY BASIN


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GEOLOGICAL MAPPING : REGIONAL MAPS

GEOCHEMICAL PROSPECTING: ANOMALY MAPS

GEOPHYSICAL PROSPECTING

GRAVITY MAGNETIC SURVEY: MAPS

SEISMIC SURVEY 2D & 3D : ISOCHRON MAPS PROSPECT IDENTIFICATION

ESTABLISHING STRATIGRAPHY : Age determination

DEPOSITIONAL ENVIRONMENTS: Facies modelingSOURCE ROCK GEOCHEMISTRY: Maturation

SYNTHESIS AND ATTRIBUTE MAPPING

STRUCTURE AND TECTONIC MAKEUPPREPARATION OF ISOCHRON-STRUCTURE MAPS

DRILLING AND SYNTHESIS OF SUBSURFACE DATA

RESERVOIR MODELLING & DEVELOPMENT SCHEME

EXPLORATION ACTIVITIES IN A SEDIMENTARY BASIN

G l i lGEOLOGICAL MAP AND CROSS SECTION OF AREA


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Geological section

Geological map

GEOCHEMICAL MAPS


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Etah area, Ganga Basin

Isochron map at the base ofTertiary

Geochemical anomalymap


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RESIDUAL GRAVITY MAP OF NORTHERN PART OF PUNJAB PLAINS

BEAS FAULT

MAGNETIC ANOMALY MAP (VERTICAL COMPONENT)


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Punjab Plains

ADAM

PURBASEM

ENTRIDGE

DINANAGAR HIGH

MUKERIAN-D

ASUYA-HOSHIARPURL

OW

LOW

TREND

HIGHTREND

LOWTR

END

HIGHTREND

HIGHTR

ENDLO

WT

REND

Beas

fault

Jalandhar

Batala

Pathankot

after Goha et al

N

0 10000 20000 30000 40000

Scale (meters)

MAGNETIC ANOMALY MAP (VERTICAL COMPONENT)


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Seismic Acquisition


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Seismic Data Acquisition Geometries

Geophones

*Seismic Energy Source

*

Shot 1

PROCESSED SEISMIC SECTION


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PROCESSED SEISMIC SECTION

INTERPRETED SEISMIC SECTION


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Kumbakonam ridge

Karaikal

ridgeTranquebar

Sub-basin

Albian

Turonian

K/T

Eocene


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PROBABLE TRAPPING MECHANISM FOR

HYDROCARBONS IDENTIFIED BY SEISMIC SURVEY

PROSPECT IDENTIFICATION


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GS-15-9

MIOPLI

OCUT

GAS SANDGS-46-1

PRESENT DEPTH

TARGET DEPTH

RANDOM SEISMIC LINE THROUGH PROSPECT GS-15-9

PROSPECT IDENTIFICATION


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SEDIMENTARY BASIN MAPSPITI-ZANSKAR

KAREWA


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BEN-GAL

SATPURA

850E DEEP

OFFSHORE

KUTCHKUTCH

GANGA

BAY

OFBENGAL

OF INDIA

OFF.

COMORIN

KORI-

SOUTHREWA

SOUTHSOUTHREWAREWA

ANDAMAN-

NICOBAR

CATEGORY - II BASINCATEGORY - I BASIN

CATEGORY - III BASIN

CATEGORY - IV BASIN

DEEP SEA BASIN

PRE-CAMBRIAN BASEMENT /TECTONISED SEDIMENTS

LEGENDLEGENDLEGEND

HIMALAYAN FORELAND

KERALAKERALA -- KONKANKONKAN --

ASSAM SHELF

ASSAM-ARAKANFOLD BELT

NARCODAM

DEEP OFFSHORE

KRISHNA

GODAVARI

CAMBAY

SAURASHTRA

RAJASTHANRAJASTHANDAMODAR

BOMBAY

OFF. DECCAN

SYNECLISE

BASTARCHATTIS-

GARH

MAHANADI

PRANHITA-GODAVARI

CUDDAPAH

CAUVERYCAUVERY

DEEP

NARMADA

BHIMA-KALADGI

VINDHYAN

AREA 3.14 Million Sq. Km.

After Jokhan ram et-al.


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GLACIAL-ALLUVIAL FANS-FLUVIAL-LACUSTRINE-DELTA AND MARINE

DEPOSITIONAL ENVIRONMENTS


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DEPOSITIONAL ENVIRONMENTS

ALLUVIAL FAN DEPOSITS


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TIDAL DEPOSITIONAL ENVIRONMENT


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DEEP WATER DEPOSITIONAL ENVIRONMENT


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CHARACTERISTICS OF DEEP WATER SEDIMENTS.Basin: Cauvery FORMATION : KAMALAPURAM


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CO

Core photograph of segments in enlarged view from (CC-2 &3) KMP-19. A (1966-1966.25m),

B (1974.85 -1975.0m) represents, convolute bedding (CO). Photos C & D are from CC-2&3 of

KMP-35. C (1868.60-1868.90m) show slump (S) and convolute layer and at bottom with parallel

oriented clasts (C ) in laminar flow (l) with primary glide plane (PG). D (1872.75-1873.10m)shows two freezing flow (f) with contact (Con). Liquefied slump (s) towards the top of bottom flow.

CO

R

C D

PG

S

C

l

f

s

f

con

A B

Age : Eocene Bathymetry: Bathyal

Interpretation: SLUMP FACIES

INTEGRATION AND UNDERSTANDING OF THE

CONCEPTS OF PETROLEUM GEOLOGY IN INDIAN


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CONCEPTS OF PETROLEUM GEOLOGY IN INDIAN

SEDMENTARY BASIN LED TO DISCOVERY OF

SIGNIFICANT HYDROCARBON DISCOVERIES.

1958:

Cambay Basin

1967:

Rajasthan

Basin

1889:

Assa

mShelf *

1974:

Mumbai

Offshore

1980:

KG

Basin

1973:

A&AA

FB

1985:Cauve

ry

Basin


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UNDERSTANDING OF THE CONCEPT OF

PETROLEUM GEOLOGY

IS A CONTINUOUS PROCESS AND

WE NEED YOUR PARTICIPATION

TO HAVE MORE SUCH DISCOVERIES

Concepts of Petroleum Geology

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