concepts of petroleum geology
TRANSCRIPT
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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