Chapter 3 (Petroleum Systems, Origin and Migration)

8/9/2019 Chapter 3 (Petroleum Systems, Origin and Migration)

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Chapter 3

Petroleum Systems

The Origin of Oil & GasSource Rocks, Generation and

Migration

1

Presenter: Leigh Brooks


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Major producing Shales in USA

+Eagle Ford Shale


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The Petroleum System

Is! The essential elements and processes and allgenetically"related hydrocarbons that occur inpetroleum sho#s and accumulations #hoseprovenance is a single pod of active source rock!

Source Rock

Migration Route

Reservoir Rock

Seal Rock

Trap

Elements

Generation and

Expulsion

Migration

Accumulation

Preservation

Processes


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24803

Petroleu# S"ste# &le#entsPetroleu# S"ste# &le#ents

Source $ockSource $ock

Top Seal $ockTop Seal $ock

$eservoir $ock$eservoir $ock

!nticlinal 'rap!nticlinal 'rap

(Organic $ich%(Organic $ich%

(Impermeable)

(Porous/Permeable)

PotentialMigration Route

Petroleum System elements

critical components of a productive system


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24803

Petroleu# S"ste# &le#entsPetroleu# S"ste# &le#ents

'20*'20*

350*350*GenerationGeneration

MigrationMigration

Seal $ockSeal $ock

$eservoir$ock$eservoir$ock

OilOil

+ater+ater

as)apas)ap

&ntrap#ent&ntrap#entAccumulation

andpreservation

Source Rock

Petroleum Systemprocesses that act on the elements to result in a hydrocarbon accumulation! eneration

discussed here is for ther#all" #ature sedi#ents! -ote biogenic or bacterial

gas forms at lo# temperatures

.'00deg )

.'/5deg )

and expulsion


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Generation " 0urial of source rock to a temperature andpressure regime sufficient to convert organic matter

into hydrocarbon! 1ifferent types of organic matter re2uiredifferent temperatures to produce oil! Sufficient volumes ofhydrocarbon need to be generated #ithin the source rock tocreate high enough pressures to force epulsion of thehydrocarbon from the source rock

Migration 34pulsion of hydrocarbon out of the source

rockand movement up#ards and into a trap, if present

'i#ing " for effective entrapment, trap must form before orduring hydrocarbon migration

!ccu#ulation " A volume of hydrocarbon that migrates intoa trap faster than the trap leaks results in an accumulation

Preser(ation " 5ydrocarbon remains in the reservoir and is

not too adversely affected by biodegradation or #ater"#ashing

Petroleum System processes


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Diagenesis

Ro = 0.5

Ro = !.0

Catagenesis

Metagenesis

K4

K3

K2

K1

K

K

Oil Phase"Out

Oil Gas

Oil Gas

Oil Gas

Cond

Gas

Gas

Less *"drogen More *"drogen

#erogen

Onset of OilGeneration

Horsield and Rullkotter! 1994

0urial to

reater

and 5otter1epths

eneration " Thermal maturation history

thermal cracking of kerogen to form hydrocarbons


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400 300 200 100

Paleo"oic Meso"oic Cen#

P $KJTPM% P Litholog&

Rock

Unit

%epth

(Km)

Source

Reservoir

Seal

Overburden

1

2

3

Placer Fm

George Sh

Boar Ss

%eer Sh

Elk Fm

Top gas 'indo'

Critical Moment

Thick

Fm

R

Magoon and %o'! 1994

Generation

Time of 34pulsion and 6igration! (Trap must already e4ist for oiland gas to be trapped%

Top oil 'indo'

Timing " 0urial history chart plot of depth andmodelled temperature vs geological time to estimate #hen generation occurred

'i#e #ill "rs

+eore

present


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1 2

400 300 200 100

Paleo"oic Meso"oic Ceno"oic

% M P P TR J K P $

Geologic Time(ScaleMill &rs beore present

PetroleumSystem Events

Source Rock

Reservoir Rock

Seal Rock

Overburden

Trap FormationGeneration! Migration!and Accumulation

Preservation

Critical Moment1# estern $orthSlope2# East(central $orthSlope

Petroleum Systems 3vents )hart to #ork

out #hether essential elements are present and the timing good-orth Slope, Alaska

'i#ing is critical

0


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Spill PointSpill Point

Seal Rock(Mudstone)Reservoir Rock

(Sandstone)Migration rom*Kitchen+

1$ Early Generation

!$ %ate Generation

Gas displaces all

oil

Gas beginning todisplace oil

%isplaced oil

accumulates

Petroleu# S"ste# A%&namic Entit&


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34ample petroleum system7 )ritical moment determined by

0urial history chart plot of depth and modelled temperature vs geologicaltime (millions of years before present% to estimate #hen generation occurred

400 300 200 100

Paleo"oic Meso"oic Cen#

P $KJTPM% P Litholog&

Rock

Unit

%epth

(Km)

Source

Reservoir

Seal

Overburden

1

2

3

Placer Fm

George Sh

Boar Ss

%eer Sh

Elk Fm

Top gas 'indo'

Critical Moment

Thick

Fm

R


Generation

2506a "Time of 34pulsion and 6igration due to rapid burial!

Top oil 'indo'

0


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An e4ample Petroleum System at )ritical interval of time

(6oment% " map or plan vie#

Magoon and %o'!1994

Teapot O'ens

Pod o Active

Source Rock Just

Big Oil

Hard& Luck&

,ero Edge o

Reservoir Rock

Immature Source Rock

Raven

Marginal

!50 Ma million years ago$

A A

%avid


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PO% OF ACTIVE SOURCE

ROCK

34ample Petroleum System at )ritical 6oment

)ritical 6oment 8 Time of 34pulsion96igration


Over'urden

Seal

Reservoir

Source

STRATIGRAPHIC

E-TE$T OF

PETROLEUM SYSTEM

Trap Trap

Essential

elements opetroleum

s&stem

Under'urdenSedim

entary

'asin

"fill

GEOGRAP(ICEXTENT O) PETRO%EUMS*STEM

!50 MaTrap

Petroleum accumulation

Top o oil 'indo'

Bottom o oil 'indo'

Location or burial histor& chart

A A

!50 Ma million years ago$


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400 300 200 100 Geologic Time

Scale

Petroleum

S&stem Events

Rock Units

Source Rock

Reservoir Rock

Seal Rock

Trap Formation

Overburden Rock

Gen/Migration/Accum

Preservation

Critical Moment

Paleo"oic Meso"oic Ceno"oic

% M P P TR J K P $

Elemen

ts

Processes

Magoon and %o'!1994

Petroleum System 3vents )hartTiming of 3lements and Processes

Critical Moment

Time of 34pulsion and 6igration! (Trap must already e4ist%

0


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GEOGRAP(ICEXTENT O) PETRO%EUMS*STEM

Present"Day

STRATIGRAPHIC

E-TE$T OF

PETROLEUM SYSTEM

Petroleum accumulationTop o oil 'indo'

Bottom o oil 'indo'

Trap TrapTrap

Seal

Reservoir

Source

Under'urden

Over'urden

A A


Present day e4ample Petroleum system cross section

vie# "things have changed since the critical moment

-ote this pool #as

charged early, before

the latest structuring,

#hich separated this

trap from the source!+ithout #orking out

the timing of

generation and

migration, you might

conclude this structure

could not contain

hydrocarbons due tono viable migration

path#ay from mature

source


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Petroleum consists mainly ofhydrocarbons, composed of )and 5 atoms (oil, condensate,

gas%! Other components mayinclude -itrogen, O4ygen,Sulphur and traces of metals

)omprises a large number of

compounds ranging from gasto solid ()' to )50%, #hich canbe divided into % #aingroups: aro#atics,napthenes, +ranchedalkanes and nor#al alkanes

Oils have average 59) of '!5"2!0and thus re2uire largeamounts of 5 for them to becreated

)omposition of Petroleum


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Origin of Oil and as Source $ocks

Petroleum is derived from organic #atter -OM) deposited in fine grainedsediments! This O6 consists of proteins, carbohydrates (incl! sugars &cellulose%, lignins (in #ood and bark% and lipids (vegetable oils, fats and#a4es%

T#o main sources of O6" '! auatic organis#s gro/ing in oceans and lakes, mainly algaeand phytoplankton (microscopic plants% and bacteria! :sually v minoranimal remains (;ooplankton, eg foraminifera #hose shell remains formchalk, radiolarians, crustaceans such as krill, etc%

" 2! remains of terrestrial -land) plants carried to the site of deposition

! good source rock reuires a suicient concentration o OM to +epreser(ed

diatomsAlgal bloom off 3ngland

Source


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The production of plankton (floating organisms% in the #orld is prodigious!

Large amounts produced in areas rich in nutrients eg sites of up#ellingcurrents

3g #ithin the 0lack Sea every year

2!/ thousand million tons of planktonare produced, containing on the average '"3 of fatty acids and 4"

'


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Preservation of Organic matter (O6%

$e2uires an o"gen deicient -anoic) en(iron#ent o deposition,#hich commonly occurs =ust belo# the sediment #ater interface

" #here there is little destruction of O6 by aerobic bacteria andscavengers

" anaerobic bacteria #ill not destroy the O6

Areas of poor #ater circulation such as silled or ponded basins arefavourable! (good circulation leads to o4ygenated #ater and sediment"unfavourable%

Stratified #ater columns, eg thermal or saline stratification, result in poorcirculation of #ater #hich leads to stagnant conditions near the sediment

#ater interface

"

Silled basin models for

ano4ia

Scott +A0S '>>4


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Ano4ic conditions are favoured by continued optimum rate of mudstonedeposition, shielding the organic matter (O6% from potentially o4ygenated#aters! Too rapid deposition may dilute the O6 in the sediment and tooslo# allo#s more time to degrade the 2uality of the O6

5igh supply of O6 is obviously favourable to preservation of significantamounts of O6 in sediments! This re2uires a continued supply of nutrientssuch as - and P, #hich is delivered to basins in the run off from rivers orby the up#elling of deep nutrient rich #aters

As the remains of organisms decay, o4ygen is consumed, leaving o4ygendepleted #aters suitable for preservation of O6 if there is poor #atercirculation

"


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)onversion of Organic matter to kerogen

+ithin a fe# metres from the surface, biopolymers begin to beconverted into kerogen, a chemically stable, insoluble (in organicsolvents and #ater% substance consisting of huge comple4 moleculescomposed of ),5 and O! This process is largely completed atrelatively shallo# burial depths of 300"'000m

A minor soluble component of the O6 is bitumen, #hich consists ofasphaltenes, resenes and hydrocarbons derived from living material!These hydrocarbons (+io#arkers%, although small in volume areimportant because they retain the chemical characteristics of theirplant source and can thus be used to identify the particular source bed

and to correlate oils! Identifying the source of a particular oil mayassist e4ploration

eg )33alkylcyclohe4ane found in most of the oils in the Perth 0asin is found only in the3arly Triassic basal ?ockatea Shale

Source richness )oncentration of O6 is usually measured by Total Organic )arbon

(TO)% as #eight of )9 unit #eight of rock

+orld average TO) of shales .'

ood (rich% source rocks considered to have TO) @2

Very rich source rocks have TO)@5


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3volution of kerogen, including cooking

(catagenesis, sometimes spelt katagenesis% to

produce oil and gas

Thermal

generation of

petroleum


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Quality of kerogen

?erogen has been divided into 3main types, #hich #ill yield differenttypes and amounts of hydrocarbon #hen thermally mature

6any source rocks contain mi4tures of the 3main types

'"pe -!lginitic) 34cellent oil source, high in 5, derived from algae and

phytoplankton (microscopic plants%! $elatively rare and occurs inlacustrine (lake% environments or closed marine basins! 3nd membercan produce up to


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TOC 2#12T#. TOC #38T#.

Kerogen t"pes


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Source $ock for Petroleum

Dar+ organic"rich thinlaminae , result of -et season runoff Measured alues

/./ /2

TotalOrganicCar'on

!.!4 1!.20

In"PlacePetroleumS1

LOMPOC uarr& Sample

Montere& Formation! CA

(ydrogenIndex

PyrolyticallyGeneratedPetroleumS!

1 Inch


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Oil and gas are formed by the thermalcracking of organic compounds buried infine"grained rocks!

3gAlgae 8 5ydrogen rich 8 Oil"prone! Type '

+ood 8 5ydrogen poor 8 as"prone! Type3b

Types of petroleum produced

Accurate prediction of probable

hydrocarbon type and volume, based onpaleogeographic and productivity models,

is critical to e4ploration success#


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Thermal maturation Average geothermal gradient #ithin sedimentary basins is appro4imately 25"30

deg )9km! It depends on heat flo# up through the earth and thermal conductivityof the sediments and varies during the basinBs evolution! Some basins may havehigh heat flo# and be 2uite hot ie have high temperatures at relatively shallo#depths

Increased heat flo# and higher geothermal gradients occur during rifting, #henthe crust is thinnest

Temperatures increase #ith depth and for e4ample may reach '35"'50deg ) atabout 4000m

+hen kerogen in sediments is sub=ected to sufficiently high temperatures fromdeep burial, it is progressively cracked into smaller, simpler molecules

petroleum, #ith increasing temperature! This is kno#n as catagenesis If oil prone kerogen (Types I and II% is present, the first products #ill be heavier

oil! As burial continues and the temperature increases, the hydrocarbonmolecules produced become lighter, moving through the peak oil generationphase to gas" condensate and finally to the end stage #here the oil retained inthe rock is converted to methane and the kerogen to carbon!

A single source rock can produce many oils of different gravities andcharacteristics, depending on the richness of the source rock and the basinBs andoilsB histories

The temperature at #hich peak oil generation occurs is variable, depending onthe type of kerogen and the heating rate among other things, but generally

ranges bet#een ''0and '

50deg )


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Thermal maturation general relationship bet#een oil and gasgeneration and various parameters such as vitrinite reflectance ($o%, spore colour

(S)I% etc


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Organic richness is measured by routine Total Organic )arbon analyses(TO), 8 #eight of )9 unit #eight of rock as %

The degree of thermal maturity of kerogen can be measured by variousmeans and is important in assessing the history of the basin and sourcerocks! This is critical in assessing remaining e4ploration potential

6easurement methods include (itrinite relectance, Spore )olour

Inde4, e4tracted soluble hydrocarbons, $ock 3val Pyrolysis, gaschromatography, gas chromatography"mass spectrometry

The history and maturity of migrating oils can be studied if traces of theoil are trapped in small inclusions #ithin crystalline cements insandstones " 6olecular )omposition of Inclusions

6easurements


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34pulsion and migration

+hen hydrocarbons are formed from the thermal degradation of kerogenthere is an increase in volume ie the oil and gas occupies more spacethan the kerogen! +hen sufficient volumes (high saturation% aregenerated #ithin the source rock, the high pressures produced #ithin thesource rock #ill cause microfracturing of the rock to occur and some ofthe hydrocarbon #ill be epelled into surrounding more porous and

permeable (and lo#er pressured% rock!

34pulsion from rich source rocks #ill occur earlier than in poorer sourcerocks because the critical volume of hydrocarbon #ithin the rock isreached sooner

"


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34pulsion and migration

Oil and gas e4pelled into more permeable neighbouring rock such assiltstone and sandstone beds in clastic sediments and into fractures then#igrates up#ards through buoyancy effects, as the petroleum is lighterthan #ater! 1riven by pressure gradients resulting from the buoyancy, theoil and gas takes the easiest path!

"


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*oreland 0asins7 Oil (and gas% in the 3astern Vene;uelan 0asin has

travelled .200

km along simple path#ays to the edge of the basin, #hereover '200billion barrels of biodegraded heavy oil is trapped at shallo#depths in the Orinoco Tar 0elt

Overburden #edge of

sediments shed off

mountains pushed sourcerocks into generation #indo#


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TrinidadBs Tar Lake migration to the surface

" #here biodegradation occurs, creating heavy oil9tar


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)hemical relations bet#een petroleum hydrocarbons

and other natural hydrocarbons6

Sh l Oil d G


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Shale Oil and Gas

Large a#ounts o oil and gas /ill re#ain /ithin ther#all" #atureorganic rich shales -source rocks) even if the shale has been throughthe peak oil generation #indo# and large amounts of oil and gas havebeen e4pelled! 34pulsion efficiency in shales is variable and depends onthe presence of interbedded permeable carrier beds

Porosity of viable shale in shale gas plays may range from 4"5 to@'0, but permeability is very lo#! 6ost of the porosity is in nanoporesformed as the O6 is converted to hydrocarbon

:ntil recently, these shales #ere considered non reservoir (in factseals%, but

If these shales have some natural fracture net#ork and the rightmechanical characteristics (primarily brittleness% to enable them to befractured (fracced% to produce the hydrocarbons contained #ithin, the"#a" +eco#e a (alua+le Shale Resource

Recent de(elop#ents in hori1ontal drilling and racture sti#ulationtechniues and reduced costs allo/ (ast (olu#es o shale toproduce h"drocar+ons econo#icall"

Sh l P t l S t


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Shale as Petroleum System

! shale gas s"ste# is a sel$contained source$reser(oir$seal -$trap) s"ste#

In this system, shales that generated the gas also function

as (er" lo/ #atri per#ea+ilit" and lo/ porosit"

reser(oir rocks

The gas in shales occurs both as a free phase #ithin poresand fractures and as gas adsorbed onto organic matter

The adsorbed gas is proportional to the total organic carbon

(TO)% of the shale! *ree gas is proportional to the effective

porosity and gas saturation in the pores

Reservoir


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Lo' matrix porosit& is

increased as more pore space

is created throughconversion

o organic matter to

h&drocarbon

Total porosit& generall& 3(10.

%ata rom core and logs

Reservoir

Oil Preservation


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+hen oil has been trapped in a reservoir it can be affected by severalprocesses that #ill change the character of the oil

Nor#al #aturation! If the trapped oil is buried further and becomes hotter,the heavier more unstable compounds #ill be cracked to lighter compoundsresulting in the oil becoming lighter (higher API gravity%

2e$asphalting! If do#ndip gas migrates into the oil accumulation, heavierasphaltenes can precipitate (plugging reservoir pores% leaving a lighter oil

ater /ashing! If the oil accumulation is in contact #ith moving a2uifer#ater, the lighter gasoline range hydrocarbons (mostly )5")'0% aredissolved in the #ater and carried a#ay, leaving a heavier oil! A less severebut similar effect can be produced from long distance migration #hich mayresult in oils #ith lo# as Oil $atios (O$%

Biodegradation! This occurs #hen fresh o4ygen charged meteoric #aterscarry aerobic bacteria from the surface to the oil reservoir, #hich must be attemperatures less than about /0deg )! The aerobic bacteria eat the lightermolecules, particularly the normal alkanes, leaving heavier oil (egTrinidad%

The large tar sand accumulations in )anada and

Vene;uela are a result ofbiodegradation and #ater #ashing, at shallo# depths

Oil Preservation


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Oils ain4t oils5

0oiling is a simple single #ord


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0oiling is a simple, single"#ord

e4planation of ho# crude oil is

separated into its eight basic parts" fractionation

11

1ensity or ravity of oil


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1ensity or ravity of oil

One of the most important properties of oil #hich, among other characteristics,

determines its commercial value, is 13-SITY!

Oil density is e4pressed in industry as oil gravity! This is given in a scale

determined by the American Petroleum Institute! Oil gravity is e4pressed indegrees API CDAPIE!

The API gravity scale is based on the 0aume scale! The follo#ing e2uation is usedto go from specific gravity

oAPI 8 C'4'!59 Specific ravity(


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ATTRIBUTE AT(ABASCA CO%D%A#E A%BERTACRUDE

Saturates 12"!/ !1 0"0

Aromatics ! 1

Asphaltenes 1 16 0.1"0.!

Resins /5 44 "15

Sulfur3 4

. 4

.5 0.1"!Metals3 ppm

anadium !50 1"5

Nic+el 100 1"5

Reservoir oilviscosity3 cp

5003000 103000"1003000

1

)omparison of conventional crude and heavy oil )anada 15

Gravity 4API "2 10"1! /5


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0iogenic as (non thermal%

0iogenic gas is generated at lo# temperatures by decomposition oforganic matter by anaerobic microorganisms!

It consists mainly of methane ()'%, #ith generally minor )O2, -2 and)2(ethane%

0iogenic gas usually can be distinguished from thermogenic gas bychemical and isotopic analyses

6ore than 20 of the #orldFs discovered gas reserves are ofbiogenic origin

The factors that control the level of methane production aftersediment burial are ano4ic environment, sulfate"deficientenvironment, lo# temperature, availability of organic matter, andsufficient pore space!

This generally occurs in areas of rapid deposition and the timing of

these factors is such that most biogenic gas is generated prior toburial depths of ',000m!

'he ther#al #odel does not appl" to this gas, /hich #a" +epresent in +asins /ith no ther#all" #ature source rocks

Case stud"


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Case stud""of a relatively simple empirical approach to defining the depth to

and e4tent of potential oil e4pulsion"this approach is reasonable in areas #hich have suffered

continuous subsidence to the present day and #hich are believed

to have had relatively uniform heat flu4 through deposition

+estern Platform, Taranaki 0asin, -e# Gealand

?ey #ell Tane"', #ith detailed geochemical analyses ofpotential coally source rock intervals

-OT

3 6ore rigorous modelling of thermal history of sediments canbe done using the estimated heat flu4 from deeper #ithin thecrust and a model of the thermal conductivity of thesediments

'ane 6


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'ane$6

Wainui

Ra+opi

Basement

Potential coally andshaley source intervals

Tane"1


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Wainui

Ra+opi

W E N S

Note increasing coallycharacter from Nto S

Wainui and Ra+opi coalscorrelate into depocentre


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$akopi *ormation7 $ock"3val! Samples from Tane"'

Oil"prone

Gas"prone

Gas" &oil"prone

GNS Science unpu'l. results$

0

100

!00

/00

400

500

0 10 !0 /0 40 50 60 0 20 0

TOC-t.$

(I&mg(C/gTOC$

Coaly mst.

Shaly coal

Coal


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1ecreasingQI, ie oil

generating potential, is dueto oil having been e4pelled

from the coally sediments at

increasing temperature

This defines the maturity

level at #hich e4pulsion

occurs

Increasing maturity

6odelled generation based on geochemical analyses of the O6 in Tane"'!

1iff t O6 ill h diff t ti hi t d d t


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Standard -S values for 'ane$6 (Sykes pers comm!%

3005I, /0 TO), 34m thickness (combined coals and shaly coals andmuds%, gogi 0!34 Potential 73 MM++l8k#7 oil and 42660O39km2 gas

'00 '20 '40 '


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)onservativetop of oil #indo#

Significant oil e4pelled at

this maturity

3mpiricalmeasurements

used to estimate

top of oil e4pulsion

"consistent #ithestimated

temperature of

.'50

deg )


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sea level

Gross thic+ness of mature source roc+

Arange o depths to top o oilexpulsion 'ere used to assess

sensitivit& to estimated gross

volume o mature sediment and

hence to volume o oil expelled

and available to ill traps

3stimated 6ature +ainui9$akopi Thickness from seismic mapping


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4500m 0S* 4/00m 0S* 4>00m 0S*

Documents

Chapter 3 (Petroleum Systems, Origin and Migration)