source rock maturity & migration

8/20/2019 Source Rock Maturity & Migration

1/25

11

Source rocks, maturity & migrationSource rocks, maturity & migration

OrganicOrganic--richrich

Source RockSource Rock

Thermally MaturedThermally Matured

Organic MatterOrganic MatterOilOil


2/25

22

Organic Matter in SedimentsOrganic Matter in Sediments

Organic matter is nearly ALWAYS depositedOrganic matter is nearly ALWAYS deposited

along with the mineral grainsalong with the mineral grains

Mostly it is consumed as food, or oxidizedMostly it is consumed as food, or oxidized

Special depositional environmentsSpecial depositional environments (anoxic(anoxicconditions)conditions) may enable preservation of themay enable preservation of the

organic matter, namelyorganic matter, namely……

Anoxic Anoxic (no oxygen)(no oxygen): no water circulation, no: no water circulation, no

benthos to recycle & fine sedimentsbenthos to recycle & fine sediments usuallyusually

makes a goodmakes a good source rock (>2% TOC)source rock (>2% TOC)


3/25

33

An Average Shale An Average Shale

Mineral matter (~99%)

Organic matter (~1%)

Immobile components (90%)

The mobile components (10%)

Usually fine-grained

i.e. clay-size particles

…or more!


4/25

44

Sources of Organic MatterSources of Organic Matter

PlantsPlants

Animals Animals


5/25

55

Types of Kerogen

and Their Hydrocarbon PotentialEnvironment

KerogenType

KerogenForm

OriginHC

Potential

Aquatic

Terrestrial

I

II

III

IV

Alginite

AmorphousKerogen

Exinite

Vitrinite

Inertite

Algal bodies

Structureless debrisof algal origin

Structureless planktonicmaterial, primarily of

marine originSkins of spores and pollen,

Cuticle of leaves andherbaceous plants

Fibrous and woody plantfragments and structureless,

colloidal humic matter

Oxidized, recycled woodydebris

None

Oil

Gas,

some oil

Mainly gas

(modified from Senftle and Landis, 1991)


6/25

66

Total Organic Carbon (TOC)

Hydrocarbon

GenerationPotential

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


7/25

77

Organic-Rich

ThinLaminae

3.39%

Total OrganicCarbon

LOMPOC Quarry Sample

Monterey Formation, CA

1 Inch1 Inch

Example of Source Rock Example of Source Rock

In placepetroleum, S1

2.24%


8/25

88

Heating UpHeating Up

……

During burial to depth, sediments, andDuring burial to depth, sediments, and

their contained pore fluids, get heatedtheir contained pore fluids, get heated

Heating increases the reaction rates forHeating increases the reaction rates for

chemical processeschemical processes

This is especially important for organicThis is especially important for organic

material that gets buried along with thematerial that gets buried along with thesedimentsediment


9/25

99

MaturationMaturation

Heat + time to convertHeat + time to convertorganic matter inorganic matter in

sediments to kerogen andsediments to kerogen andmobilemobile hydrocarbonshydrocarbons

Analogous to cooking food Analogous to cooking food

Higher temperature equalsHigher temperature equalsshorter cooking time (butshorter cooking time (butdondon’ ’ t burn it!)t burn it!)

Pressures do not impactPressures do not impactmaturity, though pressurematurity, though pressuregradients influencegradients influence

direction of migrationdirection of migration


10/25

1010

MaturityMaturity

Source rocks reach maturityin basin centre earlier thanat margins, where they maynot mature at all.

As Source Rocks are buried

deeper (hotter) and for alonger period of time, theybecome increasing mature.


11/25

1111

Oil & Gas GenerationOil & Gas Generation

Vitrinite

reflectance


12/25

1212

1.5

1.0

0.5

0

0 0.05 0.10 0.15 0.20 0.25

Type II

Exinite

Type IVInertinite

Type III

Vitrinite

Type I - Alginite

4.03.7 3.5

3.02.5

0.5

1.0

1.5

2.0

4.0

A t o m i c H

: C

R a t i o

Atomic O:C Ratio

EvolutionaryPathway(Increasing

Burial/Temperature)

Oil

Gas

CO H O2 2

TAI

VR

VR =Vitrinite

Reflectance

TAI =Thermal

Alteration

Index

Van Krevelen Diagram


13/25

1313

Where Do Hydrocarbons Go ?Where Do Hydrocarbons Go ?

Up!Up! tilted carrier beds provide a lateral componenttilted carrier beds provide a lateral component

for migrationfor migration

overover--pressure regimes can influence and pushpressure regimes can influence and push

hydrocarbons laterallyhydrocarbons laterally


14/25

1414

Primary MigrationPrimary Migration

Mobile hydrocarbons IN the source rock (as aMobile hydrocarbons IN the source rock (as a

result of maturation of organic matterresult of maturation of organic matter

contained within)contained within)

Source rocks typically fineSource rocks typically fine--grained (poor flowgrained (poor flow

qualities, generally)qualities, generally)

So, can the HC get out?So, can the HC get out?

Current ideas focus on fractures to serve asCurrent ideas focus on fractures to serve asessential flow conduitsessential flow conduits

This process is called expulsionThis process is called expulsion


15/25

1515

Source Rock FracturingSource Rock Fracturing

Natural Hydraulic Fractures insiltstone/mudstone sequence

showing cyclic growth steps

300

320

340

360

380

400

420

440

460

480

0.00 5.00 10.00 15.00 20.00 25.00 30.00

Time (sec)

P r e s s u r e ( a t m )


16/25

1616

Secondary MigrationSecondary Migration

Hydrocarbons (oil, gas) buoyant, comparedHydrocarbons (oil, gas) buoyant, compared

with pore waterswith pore waters So, they move upwards (unless there areSo, they move upwards (unless there are

unusual hydrostatic pressure gradients), andunusual hydrostatic pressure gradients), and

laterally through tilted carrier bedslaterally through tilted carrier beds

They form part of the fluid system of theThey form part of the fluid system of the

basin... And move most quickly andbasin... And move most quickly andefficiently through porous and permeableefficiently through porous and permeable

“ “carrier bedscarrier beds” ”


17/25

1717

Migration PathwaysMigration Pathways – – Charge QualityCharge Quality

Limited supply to

large region


18/25

1818

Spill PointSpill Point

Seal Rock(Mudstone)Reservoir Rock

(Sandstone)Migration from‘Kitchen’

1) Early Generation

2) Late Generation

Gas displaces alloil

Gas beginning todisplace oil

Displaced oil

accumulates

Different Phases of GenerationDifferent Phases of Generation


19/25

1919

Migration ModelingMigration Modeling

Oil

Oil with

gas cap


20/25

2020

Source Rock / Oil MatchingSource Rock / Oil Matching

Same !

Pyrolysis experiments inthe lab also allow

charge potential of apotential source rock,

and hydrocarbon typesto be determined


21/25

2121

Caveat: biodegradationCaveat: biodegradation

In some reservoirs, particularly shallowIn some reservoirs, particularly shallowaccumulations with active aquifer systemsaccumulations with active aquifer systems

(or where there has been a long(or where there has been a long

production history), bacterial action canproduction history), bacterial action cancause biocause bio--degradation. This can result indegradation. This can result in

alteration to heavy and viscous tar likealteration to heavy and viscous tar like

deposits.deposits.


22/25

2222

Maturity =Maturity =Oilfields in NOilfields in N

SeaSea


23/25

2323

Maturity =Maturity =

GasfieldsGasfields

in Australiain Australia

Post-mature

Immature


24/25

2424

ExerciseExercise

What are the various source rocks in yourWhat are the various source rocks in your ““casecasestudy basinstudy basin””??

Are these source rocks oil or gas prone? What isAre these source rocks oil or gas prone? What istheir quality (TOC?, Vitrinite Reflectance?)their quality (TOC?, Vitrinite Reflectance?)

In which areas are they mature (draw sketchIn which areas are they mature (draw sketchmap)?map)?

What was the timing of their generation (add toWhat was the timing of their generation (add toPetroleum Systems Events Chart)?Petroleum Systems Events Chart)?

What sort of volumes of hydrocarbon could yourWhat sort of volumes of hydrocarbon could yoursource rocks ultimately produce? Assume 30%source rocks ultimately produce? Assume 30%expulsion of the TOC as hydrocarbon.expulsion of the TOC as hydrocarbon.


25/25

2525

SummarySummary – – we have looked at:we have looked at:

What is a source rock What is a source rock

Source rock qualitySource rock quality

Controls on source rock maturityControls on source rock maturity

What hydrocarbons can be generatedWhat hydrocarbons can be generated

Migration (primary & secondary)Migration (primary & secondary) Quality of the chargeQuality of the charge

Multiphase migration; early & late generationMultiphase migration; early & late generation

Matching source rocks with reservoirMatching source rocks with reservoir

hydrocarbons; in lab & across basinshydrocarbons; in lab & across basins

Exercise on several aspects of source rocksExercise on several aspects of source rocks

source rock maturity & migration

Documents