Geology ofPetroleum Systems

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

Cross-Cutting Relationships

Angular Unconformity

Igneous Sill

A

B

C

D

EF

GHIJ

K

IgneousDike

• 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

Ter

tiar

y p

erio

d

Eon Era Period Epoch

Geologic Time Chart

Pal

eozo

icM

esoz

oic

Ce

noz

oic

Era

Rocks

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 m

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)

e

e

e

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

Hydrocarbon Generation, Migration, and Accumulation

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

Hydrocarbon Traps

• Structural traps

• Stratigraphic traps

• Combination traps

Structural Hydrocarbon Traps

SaltDiapir

Oil/WaterContact

GasOil/GasContact

Oil

ClosureOilShale Trap

Fracture Basement

(modified from Bjorlykke, 1989)

Fold Trap

Seal

OilSalt

Dome

Oil

SandstoneShale

Hydrocarbon Traps - Dome

Gas

Wate

r

Fault Trap

Oil / GasSand

Shale

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

Heterogeneity

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'sm

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 - m

(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