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 environments
to petroleum industry• Describe the origin of petroleum• Identify hydrocarbon trap types• Define and describe the important geologic
controls on reservoir properties, porosity and permeability
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, structural
geology• Structural traps
Petroleum System - A Definition• A Petroleum System is a dynamic hydrocarbonsystem that functions in a restricted geologicspace and time scale.
• A Petroleum System requires timelyconvergence of geologic events essential tothe formation of petroleum deposits.
These Include:Mature source rockHydrocarbon expulsionHydrocarbon migrationHydrocarbon accumulationHydrocarbon retention
(modified from Demaison and Huizinga, 1994)
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)
EssentialElements
ofPetroleum
System
(Foreland Basin Example)
(modified from Magoon and Dow, 1994)
O O
Sed
imen
tary
Bas
in F
ill
O
Stratigraphic Extent of
PetroleumSystem
Pod of ActiveSource Rock
Extent of Prospect/Field
Extent of Play
Basic Geologic Principles
• Uniformitarianism• Original Horizontality• Superposition• Cross-Cutting Relationships
• 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 sedimentary
rocks overlie older metamorphic or intrusive igneous rocks
Types of Unconformities
Correlation
• Establishes the age equivalence of rock layers in different areas
• Methods:– Similar lithology– Similar stratigraphic section– Index fossils– Fossil assemblages– Radioactive age dating
0
50
100
150
200
250
300
350
400
450
500
550
600
0
10
20
30
40
50
60
Cry
pto
zoic
(Pre
cam
bri
an)
Phanerozoic
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Pennsylvanian
Mississippian
Devonian
Silurian
Ordovician
Cambrian
Mill
ion
s o
f y
ears
ag
o
Mill
ion
s o
f y
ears
ag
o
Bill
ion
s o
f y
ears
ag
o0
1
2
3
4
4.6
Paleocene
Eocene
Oligocene
Miocene
Pliocene
PleistoceneRecent
Qu
ater
nar
yp
erio
d
Tert
iary
per
iod
Eon Era Period Epoch
Geologic Time Chart
Pal
eozo
icM
esoz
oic
Ce
noz
oic
Era
Classification of RocksSEDIMENTARY
Ro
ck-f
orm
ing
pro
cess
So
urc
e o
fm
ater
ial
IGNEOUS
METAMORPHIC
Molten materials in deep crust andupper mantle
Crystallization(Solidification of melt)
Weathering anderosion of rocks
exposed at surface
Sedimentation, burial and lithification
Rocks under high temperatures
and pressures in deep crust
Recrystallization due toheat, pressure, or
chemically active fluids
The Rock Cycle
Magma
MetamorphicRock
SedimentaryRock
IgneousRock
Sediment
Heat and Pressure
Weathering,Transportationand Deposition
Weathering, Transportation,
and Deposition
Cooling and
SolidificationM
eltin
g (Crystalization)
Hea
t And
Pre
ssur
e
(Met
amor
phis
m)
Weathering,
Transportation
And D
eposition
Cementation andCompaction(Lithification)
Siltstone, mudand shale
~75%
Sedimentary Rock Types
• Relative abundanceSandstone
and conglomerate~11%
Limestone anddolomite
~13%
Quartz Crystals
Naturally Occurring Solid
Generally Formed byInorganic Processes
Ordered InternalArrangement of Atoms(Crystal Structure)
Chemical Compositionand Physical PropertiesFixed or Vary WithinA Definite Range
Minerals - Definition
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
<5
3
<3
5
65
10-15
15
<1
<1
(modified from Blatt, 1982)
The Physical and Chemical Characteristicsof Minerals Strongly Influence the Composition of Sedimentary Rocks
Quartz
Feldspar
Calcite
Mechanically and Chemically StableCan Survive Transport and Burial
Nearly as Hard as Quartz, butCleavage Lessens Mechanical StabilityMay be Chemically Unstable in SomeClimates and During Burial
Mechanically Unstable During TransportChemically Unstable in Humid Climates Because of Low Hardness, Cleavage, andReactivity With Weak Acid
Some Common Minerals
Silicates
Oxides Sulfides Carbonates Sulfates Halides
Non-Ferromagnesian(Common in Sedimentary Rocks)
AnhydriteGypsum
HaliteSylvite
AragoniteCalciteDolomiteFe-DolomiteAnkerite
PyriteGalenaSphalerite
Ferromagnesian(not common in sedimentary rocks)
HematiteMagnetite
QuartzMuscovite (mica)Feldspars Potassium feldspar (K-spar) Orthoclase Microcline, etc . Plagioclase Albite (Na-rich - common) through Anorthite (Ca-rich - not common)
OlivinePyroxene AugiteAmphibole HornblendeBiotite (mica)
Red = Sedimentary Rock- Forming Minerals
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 replace framework grains
• Pores– Voids between above components
Norphlet Sandstone, Offshore Alabama, USAGrains are About =< 0.25 mm in Diameter/Length
PRF KF
P
KF = Potassium Feldspar
PRF = Plutonic Rock Fragment
P = Pore
Potassium Feldspar isStained Yellow With aChemical Dye
Pores are ImpregnatedWith Blue-Dyed Epoxy
CEMENT
Sandstone Composition Framework Grains
Scanning Electron MicrographNorphlet Formation, Offshore Alabama, USA
Pores Provide theVolume to ContainHydrocarbon Fluids
Pore Throats RestrictFluid Flow
PoreThroat
Porosity in Sandstone
Secondary Electron Micrograph
Jurassic Norphlet SandstoneHatters Pond Field, Alabama, USA (Photograph by R.L. Kugler)
Illite
SignificantPermeabilityReduction
Negligible PorosityReduction
Migration ofFines Problem
High IrreducibleWater Saturation
Clay Minerals in Sandstone ReservoirsFibrous Authigenic Illite
Secondary Electron Micrograph
Jurassic Norphlet SandstoneOffshore Alabama, USA (Photograph by R.L. Kugler)
Occurs as ThinCoats on DetritalGrain Surfaces
Occurs in SeveralDeeply BuriedSandstones WithHigh Reservoir Quality
Iron-Rich Varieties ReactWith Acid
~ 10 mm
Clay Minerals in Sandstone ReservoirsAuthigenic Chlorite
Secondary Electron Micrograph
Carter SandstoneNorth Blowhorn Creek Oil UnitBlack Warrior Basin, Alabama, USA
Significant PermeabilityReduction
High Irreducible WaterSaturation
Migration of FinesProblem
(Photograph by R.L. Kugler)
Clay Minerals in Sandstone ReservoirsAuthigenic Kaolinite
100
10
1
0.1
0.01 0.01
0.1
1
10
100
1000
2 6 10 14 2 6 10 14 18
Per
mea
bili
ty (
md
)
Porosity (%)
Authigenic Illite Authigenic Chlorite
(modified from Kugler and McHugh, 1990)
Effects of Clays on Reservoir Quality
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
Diagenesis
CarbonateCemented
OilStained
Diagenesis is the Post-Depositional Chemical andMechanical Changes thatOccur in Sedimentary Rocks
Some Diagenetic Effects Include
CompactionPrecipitation of CementDissolution of Framework Grains and Cement
The Effects of Diagenesis MayEnhance or Degrade ReservoirQuality
Whole CoreMisoa Formation, Venezuela
Fluids Affecting Diagenesis
Precipitation
Subsidence
CH4,CO2,H2S
Petroleum Fluids
Meteoric Water
Meteoric Water
COMPACTIONAL WATER
Channel
Flow
EvapotranspirationEvaporation
Infiltration
Water Table
Zone of abnormal pressure
Isotherms
Atmospheric Circulation
(modified from from Galloway and Hobday, 1983)
Thin Section Micrograph - Plane Polarized LightAvile Sandstone, Neuquen Basin, Argentina
Dissolution ofFramework Grains(Feldspar, for Example) and Cement may Enhance theInterconnected Pore System
This is CalledSecondary Porosity
Pore
Quartz DetritalGrain
PartiallyDissolvedFeldspar
(Photomicrograph by R.L. Kugler)
Dissolution Porosity
Organic Matter in Sedimentary Rocks
Reflected-Light Micrographof Coal
Vitrinite
KerogenDisseminated Organic Matter inSedimentary Rocks That is Insolublein Oxidizing Acids, Bases, andOrganic Solvents.
VitriniteA nonfluorescent type of organic materialin petroleum source rocks derived primarily from woody material.
The reflectivity of vitrinite is one of thebest indicators of coal rank and thermalmaturity of petroleum source rock.
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
Schematic Representation of the Mechanismof 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
Metagenesis
Pro
gre
ssiv
e B
uri
al a
nd
Hea
tin
g
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 O’Conner, 1982)
Vit
rin
ite
Ref
lect
ance
(R
o)
%
Wei
gh
t %
Car
bo
n i
n K
ero
gen
Sp
ore
Co
lora
tio
n I
nd
ex (
SC
I)
Pyr
oly
sis
T(C
)m
ax
0.2
0.3
0.4
0.5
4.0
3.0
2.0
1.3
1
2
3
456
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
Reservoirrock
Seal
Migration route
Oil/watercontact (OWC)
Hydrocarbonaccumulation
in thereservoir rock
Top of maturity
Source rock
Fault(impermeable)
Generation, Migration, and Trapping of Hydrocarbons
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)
EssentialElements
ofPetroleum
System
(Foreland Basin Example)
(modified from Magoon and Dow, 1994)
O O
Sed
imen
tary
Bas
in F
ill
O
Stratigraphic Extent of
PetroleumSystem
Pod of ActiveSource Rock
Extent of Prospect/Field
Extent of Play
Structural Hydrocarbon Traps
SaltDiapir
Oil/WaterContact
GasOil/GasContact
Oil
ClosureOilShale Trap
Fracture Basement
(modified from Bjorlykke, 1989)
Fold Trap
Seal
OilSalt
Dome
Oil/Gas
Oil/Gas
Oil/Gas
Stratigraphic Hydrocarbon Traps
Uncomformity
Channel Pinch Out
(modified from Bjorlykke, 1989)
Unconformity Pinch out
Asphalt Trap
Water
MeteoricWater
BiodegradedOil/Asphalt
PartlyBiodegraded Oil
Hydrodynamic Trap
Shale
OilWater
HydrostaticHead
(modified from Bjorlykke, 1989)
Other Traps
Reservoir Heterogeneity in Sandstone
Heterogeneity MayResult From:
Depositional Features
Diagenetic Features
(Whole Core Photograph, MisoaSandstone, Venezuela)
Heterogeneity
Segments Reservoirs
Increases Tortuosity of Fluid Flow
Reservoir Heterogeneity in Sandstone
Heterogeneity Also MayResult From:
Faults
Fractures
Faults and Fractures maybe Open (Conduits) or Closed (Barriers) to Fluid Flow
(Whole Core Photograph, MisoaSandstone, Venezuela)
BoundingSurface
BoundingSurface
Eolian Sandstone, Entrada Formation, Utah, USA
Geologic Reservoir Heterogeneity
Scales of Geological Reservoir Heterogeneity
Fie
ld W
ide
Inte
rwel
lW
ell-B
ore
(modified from Weber, 1986)
Hand Lens orBinocular Microscope
Unaided Eye
Petrographic orScanning Electron
Microscope
DeterminedFrom Well Logs,Seismic Lines,
StatisticalModeling,
etc.
10-100'smm
10-100'smm
1-10'sm
100'sm
10'sm
1-10 km
100's m
Well WellInterwell
Area
ReservoirSandstone
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 - mm
(modified from Hurst, 1993)
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
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