Basics of Basics of Petroleum Petroleum GeologyGeology

Dr.Ir. Sudjati Rachmat, Dr.Ir. Sudjati Rachmat, DEADEA

HistoricalHistorical Petroleum products have been used for at least 8000 yearsPetroleum products have been used for at least 8000 years Herodotus 450 BC – natural seepsHerodotus 450 BC – natural seeps Egyptians – mummification/ Victorian medicationEgyptians – mummification/ Victorian medication Ancient Greece everlasting flame in the sacred Oracle at DelphiAncient Greece everlasting flame in the sacred Oracle at Delphi Persian Temples built around natural gas sourcesPersian Temples built around natural gas sources

Early uses: Early uses: medication, waterproofing, warfaremedication, waterproofing, warfare

Up to mid 19Up to mid 19thth century: all oil produced from seeps, shallow century: all oil produced from seeps, shallow pits and hand dug shaftspits and hand dug shafts

James Young: extracted oil from carboniferous shales, Scotland James Young: extracted oil from carboniferous shales, Scotland 1847: “oil-shales”1847: “oil-shales”

1st 1st Natural gasNatural gas:: Sichuan Province China Sichuan Province China several thousand several thousand years ago years ago Bamboo tools and pipes – salt productionBamboo tools and pipes – salt production

11stst oil-seeking well = Pechelbronn, France, 1745 oil-seeking well = Pechelbronn, France, 1745 11stst well to produce oil: Oil creek, Pennsylvania by “Colonel” well to produce oil: Oil creek, Pennsylvania by “Colonel”

DrakeDrake

The Demand for Oil The Demand for Oil ProductsProducts

Increased greatly by WWI (1914-Increased greatly by WWI (1914-18)18)

By 1920 the oil industry By 1920 the oil industry dominated by the “seven sisters”dominated by the “seven sisters”

Post WWII, oil companies began to Post WWII, oil companies began to risk profits from one productive risk profits from one productive area to explore for another.area to explore for another.

1960: Organization of Petroleum 1960: Organization of Petroleum Exporting Countries (OPEC) Exporting Countries (OPEC) formed in Baghdad (Iraq)formed in Baghdad (Iraq) Objective: control the power of the Objective: control the power of the

independent oil companies by price independent oil companies by price control & appropriation of company control & appropriation of company assetsassets

The science of petroleum The science of petroleum geologygeology

ChemistryChemistry Geochemistry is a major component of petroleum geologyGeochemistry is a major component of petroleum geology

Detailed knowledge of the mineralogical composition of rocks – Detailed knowledge of the mineralogical composition of rocks – reservoir qualityreservoir quality

Pore-fluid chemistry – reservoir degradation/ enhancementPore-fluid chemistry – reservoir degradation/ enhancement Organic geochemistry: biomarkers, fingerprintingOrganic geochemistry: biomarkers, fingerprinting

PhysicsPhysics Geophysics contribute toGeophysics contribute to

Understanding the earth’s crustUnderstanding the earth’s crust Understanding the structures involved in trapping: folds, faultsUnderstanding the structures involved in trapping: folds, faults Identifying the position of such traps: magnetics, gravity, Identifying the position of such traps: magnetics, gravity,

seismicsseismics Understanding the wells: wireline logs, lithology, porosity..Understanding the wells: wireline logs, lithology, porosity..

BiologyBiology Study of fossil life: Palaeontology contributesStudy of fossil life: Palaeontology contributes

Dating/ stratigraphic characterizationDating/ stratigraphic characterization Environmental characterization (fossil environments, Environmental characterization (fossil environments,

palaeoecology)palaeoecology) Biochemistry: transformation of plant and animal tissues into Biochemistry: transformation of plant and animal tissues into

kerogen and through to oil and gas.kerogen and through to oil and gas.

The physical and chemical The physical and chemical properties of oil and gasproperties of oil and gas

Hydrocarbon: composed of H and CHydrocarbon: composed of H and C

Gases LiquidOil, Crude

PlasticAsphalts, Coals, Kerogen

Wetethane, propane

Drymethane

Natural Gas Liquid Natural Gas Liquid (NGL)(NGL)

Classified intoClassified into

Hydrocarbon Gases

Methane (dry)

Ethane (wet)PropaneButane

ORGANIC ORIGIN

Inert GasesHeliumArgon

KryptonRadon

NitrogenAlso

Carbon dioxideHydrogen sulphide

INORGANIC ORIGIN

Crude OilCrude Oil““a mixture of hydrocarbons that existed in the liquid phase in a mixture of hydrocarbons that existed in the liquid phase in

natural underground reservoirs and remains liquid at natural underground reservoirs and remains liquid at atmospheric pressure after passing through surface atmospheric pressure after passing through surface

separating facilities”separating facilities”

Highly variable in composition and in appearanceHighly variable in composition and in appearance Primarily carbon, hydrogen and minor oxygen, nitrogen, Primarily carbon, hydrogen and minor oxygen, nitrogen,

sulphur, vanadium, nickel…sulphur, vanadium, nickel… Colour: yellow, green, brown to dark brown & blackColour: yellow, green, brown to dark brown & black Oil at the surface tends to be more viscous, most oils are less Oil at the surface tends to be more viscous, most oils are less

dense than water: generally measured as the difference dense than water: generally measured as the difference between its density and that of water:between its density and that of water:

Thus light oils have API < 10° and heavy oils are more dense Thus light oils have API < 10° and heavy oils are more dense than waterthan water

°API = 141.5

SG 60/60°F - 131.5

The 5 main components of The 5 main components of an oil accumulationan oil accumulation

1.1. Must be an organic-rich source rock to Must be an organic-rich source rock to generate the oil/ gasgenerate the oil/ gas

2.2. The source rock must have been heated The source rock must have been heated sufficiently to yield its petroleumsufficiently to yield its petroleum

3.3. There must be a reservoir to contain the There must be a reservoir to contain the expelled hydrocarbons. This must have:expelled hydrocarbons. This must have:

a.a. PorosityPorosity, to hold the hydrocarbons, to hold the hydrocarbonsb.b. PermeabilityPermeability, to allow fluid flow, to allow fluid flow

4.4. The reservoir must be sealed by an The reservoir must be sealed by an impermeable Cap Rock to prevent upwards impermeable Cap Rock to prevent upwards escape of the hydrocarbons to the earth’s escape of the hydrocarbons to the earth’s surfacesurface

5.5. Source, reservoir and seal must be arranged in Source, reservoir and seal must be arranged in such a way that the petroleum is Trappedsuch a way that the petroleum is Trapped

Formation of an oil Formation of an oil accumulationaccumulation

1.1. Burial of adequate organic source material.Burial of adequate organic source material. most petroleum is derived from the accumulation of trillions of most petroleum is derived from the accumulation of trillions of

individual micro-organisms.individual micro-organisms.

2.2. Burial to the appropriate depths.Burial to the appropriate depths. depths of 2-6 km and temperatures of 60-160º C.depths of 2-6 km and temperatures of 60-160º C.

3.3. Presence of a reservoir-quality rock.Presence of a reservoir-quality rock.1.1. a porous storage space. Sandstone and limestones are the most a porous storage space. Sandstone and limestones are the most

common reservoir rocks. To be a reservoir they must have:common reservoir rocks. To be a reservoir they must have: PorosityPorosity, to hold the hydrocarbons, to hold the hydrocarbons PermeabilityPermeability, to allow fluid flow, to allow fluid flow

4.4. Presence of an adequate sealPresence of an adequate seal A seal is an impermeable bed (such as a shale or a bed of salt) that A seal is an impermeable bed (such as a shale or a bed of salt) that

sits on top of the trap and prevents the hydrocarbons rising any sits on top of the trap and prevents the hydrocarbons rising any further.further.

5.5. Presence of a trapPresence of a trap In order to prevent the hydrocarbons rising to the surface and In order to prevent the hydrocarbons rising to the surface and

escaping they must be caught in a confined space, termed a trap. i.e. escaping they must be caught in a confined space, termed a trap. i.e. the source, reservoir and seal must be arranged in such a way that the source, reservoir and seal must be arranged in such a way that the petroleum is trapped.the petroleum is trapped.

The Petroleum SystemThe Petroleum System

In addition to the 5 components, a In addition to the 5 components, a further two events are essential:further two events are essential: TimingTiming: no trapping unless the traps : no trapping unless the traps

are present when migration is occurringare present when migration is occurring MaturationMaturation: no petroleum if the source : no petroleum if the source

rock OM does not maturerock OM does not mature MigrationMigration: no accumulation if the : no accumulation if the

petroleum doesn’t migratepetroleum doesn’t migrate

The Source RockThe Source Rock

This shale typically contains >1% of organic carbon, by weight. This shale typically contains >1% of organic carbon, by weight. The shale is very widespread, underlying much of Britain and The shale is very widespread, underlying much of Britain and most of the North Sea, and is by far the most important source most of the North Sea, and is by far the most important source rock for the oil that has been found in the North Sea Basin. rock for the oil that has been found in the North Sea Basin.

The Reservoir Rock: The Reservoir Rock: SandstoneSandstone

An outcrop of pebbly sandstone (at base of cliff) overlain by red An outcrop of pebbly sandstone (at base of cliff) overlain by red sandstone. The Budleigh-Salterton pebble beds, of Triassic age. A sandstone. The Budleigh-Salterton pebble beds, of Triassic age. A few kilometres to the east these beds dip into the subsurface, and few kilometres to the east these beds dip into the subsurface, and form part of the oil reservoir at the Wytch Farm Fieldform part of the oil reservoir at the Wytch Farm Field, which is , which is Britain’s largest onshore oil field. Britain’s largest onshore oil field.

The Reservoir Rock: The Reservoir Rock: SandstoneSandstone

The Jurassic Bridport Sand. Another of the reservoir sandstones The Jurassic Bridport Sand. Another of the reservoir sandstones important in the Wytch Farm field of southern Britain. The layering important in the Wytch Farm field of southern Britain. The layering in this sandstone may be the result of rhythmic climatic changes in in this sandstone may be the result of rhythmic climatic changes in the shallow sea where this sandstone was deposited. the shallow sea where this sandstone was deposited.

The Reservoir Rock: The Reservoir Rock: DolomiteDolomite

The Cairns Formation, of Devonian age, exposed near The Cairns Formation, of Devonian age, exposed near Canmore, in the Front ranges of the Rocky Mountains, just Canmore, in the Front ranges of the Rocky Mountains, just east of Banff, Alberta. This is one of the more important east of Banff, Alberta. This is one of the more important reservoir units in the subsurface of Alberta. reservoir units in the subsurface of Alberta.

The Reservoir Rock: The Reservoir Rock: DolomiteDolomite

This is an example of an important reservoir rock type. Fossil This is an example of an important reservoir rock type. Fossil stromatoporoids have been hollowed out by the chemical stromatoporoids have been hollowed out by the chemical conversion of limestone to dolomite, creating pore spaces so conversion of limestone to dolomite, creating pore spaces so large that they are sometimes called “large that they are sometimes called “cavernous porositycavernous porosity””

Making reservoirs today: Making reservoirs today: limestoneslimestones

An exposure of modern An exposure of modern limestone in the Florida Keys. limestone in the Florida Keys. This limestone is only a few This limestone is only a few hundred years old. It shows hundred years old. It shows the structure of coral and the structure of coral and other organic remains. other organic remains. Note Note the numerous pore spacesthe numerous pore spaces. .

Burial of this limestone would Burial of this limestone would probably lead to reduction in probably lead to reduction in porosity as a result of porosity as a result of cementation,. Good quality cementation,. Good quality reservoir rocks, such as the reservoir rocks, such as the dolomite shown in another dolomite shown in another picture, are created by picture, are created by dissolution of some of the dissolution of some of the rock. This usually occurs rock. This usually occurs many millions of years after many millions of years after the initial formation and the initial formation and burialburial

The SealThe Seal

Commonly Commonly evaporites, chalks evaporites, chalks and shales.and shales.

Relatively Relatively impermeableimpermeable

The Trap: StratigraphicThe Trap: Stratigraphic

Stratigraphic traps are traps created by the Stratigraphic traps are traps created by the limits of the reservoir rock itself, without limits of the reservoir rock itself, without any structural control. any structural control.

Here is an example of a reef trap. The Here is an example of a reef trap. The diagram shows a vertical slice (cross-diagram shows a vertical slice (cross-section) through the reservoir and section) through the reservoir and overlying rocks.overlying rocks.

Stratigraphic traps are also formed in clastic rocks: here, in a cross-section through a continental margin, two sandstone beds form traps within muddy coastal deposits. River channels may form long, thin traps corresponding to the former position of the river or delta distributary. Beach sands may form sheet-like bodies along an ancient shoreline etc.

The Trap: StructuralThe Trap: Structural Structural traps are formed where the space for Structural traps are formed where the space for

petroleum is limited by a structural featurepetroleum is limited by a structural feature

Tilted fault-block trapsTilted fault-block traps are are formed where the upward flow formed where the upward flow of the petroleum is prevented of the petroleum is prevented by impermeability along the by impermeability along the fault plane and by an fault plane and by an overlying cap or seal: common overlying cap or seal: common in the North Sea.in the North Sea.

Anticlinal trapsAnticlinal traps are formed by are formed by folding in the rocks. folding in the rocks.

Unconformity trapsUnconformity traps are are generated where an erosional generated where an erosional break in the stratigraphic break in the stratigraphic succession is followed by succession is followed by impermeable strata.impermeable strata.

The Trap: StructuralThe Trap: Structural

This type of structural trap This type of structural trap is very common in fold-is very common in fold-and-thrust belts at the and-thrust belts at the front of mountain ranges front of mountain ranges like the Rocky Mountains like the Rocky Mountains of Alberta, where older of Alberta, where older rocks are pushed sideways rocks are pushed sideways over younger rocks (e.g., over younger rocks (e.g., the yellow unit is here the yellow unit is here pushed over the light-blue pushed over the light-blue unit). unit).

Oil is pooled in anticlinal Oil is pooled in anticlinal folds.folds.

The traps may also be The traps may also be partly faulted, as in the partly faulted, as in the upper one shown here.upper one shown here.

The Subsurface The Subsurface EnvironmentEnvironment

Temperature in the Temperature in the subsurfacesubsurface

Increases towards the earth’s core: Increases towards the earth’s core: geothermal gradientgeothermal gradient Different lithologies will conduct heat Different lithologies will conduct heat

differently: thermal conductivitydifferently: thermal conductivity Additional heat added by decay of radioactive Additional heat added by decay of radioactive

speciesspecies Heat Flow = Geothermal gradient x thermal Heat Flow = Geothermal gradient x thermal

conductivityconductivityMineralMineral Thermal Thermal

conductivitconductivityy

HaliteHalite 5.55.5

LimestoneLimestone 3 – 3.53 – 3.5

SandstoneSandstone 2.5 – 42.5 – 4

CoalCoal 0.30.3

Pressure in the subsurfacePressure in the subsurface

The force per unit area acting on a surfaceThe force per unit area acting on a surface

Overburden pressure (S) = lithostatic pressure (p) + fluid pressure (f)Overburden pressure (S) = lithostatic pressure (p) + fluid pressure (f)

Column of freshwater = 0.43 psi/ft : normalColumn of freshwater = 0.43 psi/ft : normal

Abnormal (overpressured) = >0.43 psi/ftAbnormal (overpressured) = >0.43 psi/ft

Abnormal (underpressured) = <0.43 psi/ftAbnormal (underpressured) = <0.43 psi/ft

Grain-grain contact

Hydrostatic (imposed by a column of fluid at rest)Hydrodynamic (fluid potential gradient caused by fluid flow)

Temperature – Pressure Temperature – Pressure RelationshipRelationship

Boyle’s Law: (P x V)/T = constantBoyle’s Law: (P x V)/T = constant• Fluid may exist in either the liquid or gaseous form depending on the PT conditions.• Above the critical point: only 1 phase may exist

liquidgas

c

condensation

evaporation

PR

ES

SU

RE

TEMPERATURE

Mixed fluids in the Mixed fluids in the subsurfacesubsurface

Subsurface fluid may be a mixture of water and Subsurface fluid may be a mixture of water and hydrocarbon.hydrocarbon.

Petroleum is a mixture of many types of Petroleum is a mixture of many types of hydrocarbon in liquid or gaseous formshydrocarbon in liquid or gaseous forms

liquid & vapour

vapour

c

Dew point curveGas condenses

Bubble point curveGas begins to bubble out of liquid

PR

ES

SU

RE

TEMPERATURE

liquid

Modern Organic Processes Modern Organic Processes at the Earth’s Surfaceat the Earth’s Surface

SurfaceSurface 82% C locked into CO82% C locked into CO33 in carbonates in carbonates 18% occurs as organic C in coal, oil & gas18% occurs as organic C in coal, oil & gas When death occurs, a plant or animals remains are When death occurs, a plant or animals remains are

normally oxidized and COnormally oxidized and CO22/ H2O released/ H2O released SubsurfaceSubsurface

When death occurs, a plant or animals remains are When death occurs, a plant or animals remains are normally oxidized and COnormally oxidized and CO22/ H2O released/ H2O released

Under exceptional conditions: organic matter is buried Under exceptional conditions: organic matter is buried and preserved in sedimentsand preserved in sediments

The composition of the organic matter strongly The composition of the organic matter strongly influences whether the organic matter can produce influences whether the organic matter can produce coal, oil or gas.coal, oil or gas.

Basic components of Basic components of organic matter in organic matter in

sedimentssediments PROTEINSPROTEINS

More abundant in animals: O, C, N, HMore abundant in animals: O, C, N, H CARBOHYDRATESCARBOHYDRATES

Occur in both. COccur in both. Cnn(H(H22O)O)nn sugars, cellulose, starchsugars, cellulose, starch

LIPIDS (Fats)LIPIDS (Fats) Occur in both: C, H, OOccur in both: C, H, O Fats, oils, waxes (e.g. leaf cuticles)Fats, oils, waxes (e.g. leaf cuticles)

LIGNINLIGNIN Occurs in plants: complex aromatic ring structures, large Occurs in plants: complex aromatic ring structures, large

moleculesmolecules

All of these + Time + Temperature + Pressure = All of these + Time + Temperature + Pressure = KEROGENKEROGEN

Types of KerogenTypes of Kerogen Type IType I : algal kerogen : algal kerogen

““best” oil sourcebest” oil source Lipid-richLipid-rich

Type IIType II: herbaceous kerogen: herbaceous kerogen Good oil sourceGood oil source Includes zooplankton (sapropelic)Includes zooplankton (sapropelic)

Type IIIType III: woody kerogen (coaly): woody kerogen (coaly) Good gas sourceGood gas source Rich in humic componentsRich in humic components

Type IVType IV: amorphous kerogen: amorphous kerogen

What happens when we What happens when we subject kerogen to subject kerogen to

subsurface conditions?subsurface conditions?KEROGEN

Diagenesis

Catagenesis

Metagenesis

Shallow subsurfaceNormal pressure and temperatureReleased: CH4, CO2, H2O• Overall decrease in O• Overall increase in H and C

Deeper subsurfaceIncreased pressure and temperatureReleased: oil & gas• Overall decrease in H and C

MetamorphismHigh temperature and pressure Only C remains: becomes graphite

When is oil expelled?When is oil expelled?

A more refined A more refined classificationclassification

Migration of Migration of hydrocarbonshydrocarbons

PrimaryPrimary From source rock to “carrier bed”From source rock to “carrier bed”

SecondarySecondary Through the carrier bed/ structure to the reservoirThrough the carrier bed/ structure to the reservoir

How?How? As long as the oil droplets expelled are < pore throats, As long as the oil droplets expelled are < pore throats,

buoyancy will migrate the droplets until they reach a buoyancy will migrate the droplets until they reach a throat through which they cannot pass.throat through which they cannot pass.

Further movement can only occur when the Further movement can only occur when the displacement pressure of the oil exceeds the capillary displacement pressure of the oil exceeds the capillary pressure of the porepressure of the pore

This process progresses until the oil column reaches a This process progresses until the oil column reaches a rock whose pores are so small that the oil column rock whose pores are so small that the oil column pressure cannot force further movement: the oil is pressure cannot force further movement: the oil is trapped against a CAP ROCK (seal)trapped against a CAP ROCK (seal)

The Reservoir RockThe Reservoir Rock

Must have sufficient porosity (Must have sufficient porosity () to store the oil) to store the oil Must have sufficient permeability (K) to allow Must have sufficient permeability (K) to allow

fluid flowfluid flow

% = (volume of voids / total volume of rock) x % = (volume of voids / total volume of rock) x 100100

EffectiveEffective = total volume of voids that are = total volume of voids that are interconnectedinterconnected

K: measured in Darcy units (commonly K: measured in Darcy units (commonly miliDarcy)miliDarcy)

Often measured as Kv and Kh due to grain Often measured as Kv and Kh due to grain orientation/ heterogeneity issuesorientation/ heterogeneity issues

The perfect Reservoir rock:The perfect Reservoir rock: 10 – 30% 10 – 30% and 500 – 1000mD and 500 – 1000mD Well sorted, medium-coarse grain sizeWell sorted, medium-coarse grain size Laterally continuous with no poor RQ intervals/ Laterally continuous with no poor RQ intervals/

faciesfacies

Kv

Khx

Khz

The TrapThe Trap

A subsurface obstacle to flow of A subsurface obstacle to flow of petroleum to the earth’s surface.petroleum to the earth’s surface.

Classified (broadly) intoClassified (broadly) into Structural TrapsStructural Traps

Formed by tectonism, diapirism, gravitational and Formed by tectonism, diapirism, gravitational and compactional processes, e.g. folds and faults.compactional processes, e.g. folds and faults.

Stratigraphic TrapsStratigraphic Traps Trap geometry is essentially inherited from the Trap geometry is essentially inherited from the

original depositional architecture, e.g. pinchout and original depositional architecture, e.g. pinchout and unconformity trapsunconformity traps

Hydrodynamic TrapsHydrodynamic Traps

Petroleum Petroleum Geology in South Geology in South

AfricaAfrica

General country General country statisticsstatistics

4% total area of Africa, 4% total area of Africa, 6% total population: 6% total population: uses 50% of continent’s uses 50% of continent’s electricityelectricity

Population of 43.7 Population of 43.7 millionmillion

GDP (2000) $126 billionGDP (2000) $126 billion Services 64%Services 64% Manufacturing 25%Manufacturing 25% Mining and quarrying 7%Mining and quarrying 7% Agriculture 4%Agriculture 4%

GDP per head $3160 GDP per head $3160 (highest in Africa)(highest in Africa)

0

10

20

30

40

50

60

70

1st Qtr

Services

Manufacturing

Mining &QuarryingAgriculture

Energy in SAEnergy in SA Primary energy resource is coalPrimary energy resource is coal

Easily exploited large depositsEasily exploited large deposits 55 billion tonnes reserves: 755 billion tonnes reserves: 7thth in world in world 66thth largest coal producer in world: 200 Mtons/yr largest coal producer in world: 200 Mtons/yr 91% coal produced is used in SA91% coal produced is used in SA

Mostly for electricity and synthetic fuel productionMostly for electricity and synthetic fuel production Thus coal supplies 77+% total energy market of SAThus coal supplies 77+% total energy market of SA

SA has 14% western worlds uranium resourcesSA has 14% western worlds uranium resources Mostly produced as by-product of gold miningMostly produced as by-product of gold mining

So: self-sufficient in terms of coal and uranium So: self-sufficient in terms of coal and uranium energy resources BUT environmentally not a perfect energy resources BUT environmentally not a perfect scenario: cleaner gas energy sources may become scenario: cleaner gas energy sources may become more important.more important.

Petroleum in SAPetroleum in SA

65% required crude oil is imported and refined in 65% required crude oil is imported and refined in SASA

Current consumption: 490,000 bbl/dCurrent consumption: 490,000 bbl/d Balance (35%) is made up from:Balance (35%) is made up from:

Liquid fuels from coal (Sasol process) Liquid fuels from coal (Sasol process) 150,000 bbl/d crude oil equivalent150,000 bbl/d crude oil equivalent 23% of SA requirements23% of SA requirements

Domestic oil fields, Domestic oil fields, OribiOribi OryxOryx SableSable 6% of SA requirements6% of SA requirements

Modified Sasol process: offshore gas and condensate Modified Sasol process: offshore gas and condensate converted to liquid fuelsconverted to liquid fuels

45,000 bbl/d45,000 bbl/d 5% of SA requirements5% of SA requirements

The offshore The offshore environmentenvironment

South Africa is a large South Africa is a large country: more than 1.1 country: more than 1.1 million sq km and its million sq km and its coastline has a total length of coastline has a total length of nearly 3000 km. nearly 3000 km.

The west coast, from the The west coast, from the Orange River to Cape Point, Orange River to Cape Point, is almost 900 km long and is almost 900 km long and the remainder, from Cape the remainder, from Cape Point to Ponta do OuroPoint to Ponta do Ouro

on the Mozambique border, on the Mozambique border, is more than 2000 km long.is more than 2000 km long.

The continental shelf is 20-The continental shelf is 20-160 km wide off the west 160 km wide off the west coast, 50-200 km wide off the coast, 50-200 km wide off the south coast, but rarely more south coast, but rarely more than 30 km wide on the east than 30 km wide on the east coast, except along the coast, except along the Durban basin. Durban basin.

Similarly the continental Similarly the continental slope is fairly wide on the slope is fairly wide on the west and south coasts but west and south coasts but narrow to the east.narrow to the east.

Exploration & Production Exploration & Production HistoryHistory

1940’s1940’s: First organised search for hydrocarbons in South Africa : First organised search for hydrocarbons in South Africa (GSA). (GSA).

19651965 Soekor (Pty) Ltd formed by the government and began its Soekor (Pty) Ltd formed by the government and began its search in the onshore areas of the Karoo, Algoa and Zululand search in the onshore areas of the Karoo, Algoa and Zululand Basins.Basins.

19671967 a new Mining Rights Act was passed : offshore concessions a new Mining Rights Act was passed : offshore concessions were granted to a large numberwere granted to a large number

of international companies including Total, Gulf Oil, Esso, Shell, of international companies including Total, Gulf Oil, Esso, Shell, ARCO, CFP and Superior. ARCO, CFP and Superior.

This led to the first offshore well being drilled in 1969 and the discovery This led to the first offshore well being drilled in 1969 and the discovery by Superior of gas and condensate in the Ga-A1 well situated in the by Superior of gas and condensate in the Ga-A1 well situated in the Pletmos Basin.Pletmos Basin.

19701970: Soekor (together with Rand Mines) extended its efforts to the : Soekor (together with Rand Mines) extended its efforts to the offshore but, despite further encouraging discoveries, international offshore but, despite further encouraging discoveries, international companies gradually withdrew. companies gradually withdrew.

This was largely as a result of political sanctions against South Africa. This was largely as a result of political sanctions against South Africa. Thus from the mid-1970’s to the late 1980’s Soekor, the State owned Thus from the mid-1970’s to the late 1980’s Soekor, the State owned

oil and gas exploration company, was the sole explorer operating the oil and gas exploration company, was the sole explorer operating the entire offshore area of South Africa.entire offshore area of South Africa.

Since 1997Since 1997: offshore areas have been opened to international : offshore areas have been opened to international investors. To date, 4 exploration leases and 3 study agreements have investors. To date, 4 exploration leases and 3 study agreements have been signed.been signed.

Exploration & Production Exploration & Production HistoryHistory

In the entire offshore area there are now 287 exploration wells In the entire offshore area there are now 287 exploration wells including appraisal and production wells.including appraisal and production wells.

In addition approximately 250 000 km of 2D seismic data and In addition approximately 250 000 km of 2D seismic data and about 4 500 km of 3D seismic data have been acquired since about 4 500 km of 3D seismic data have been acquired since exploration began offshore.exploration began offshore.

Exploration drilling was most active from 1981 to 1991 during Exploration drilling was most active from 1981 to 1991 during which period some 181 exploration wells were drilled. which period some 181 exploration wells were drilled.

The Bredasdorp Basin has been the focus of most seismic and The Bredasdorp Basin has been the focus of most seismic and drilling activity since 1980.drilling activity since 1980.

The results of this exploration are the discovery of twenty gas The results of this exploration are the discovery of twenty gas fields and nine oil fields, and the commercial production of oil and fields and nine oil fields, and the commercial production of oil and gas. gas.

In the Pletmos Basin there are two undeveloped gas fields and a In the Pletmos Basin there are two undeveloped gas fields and a further sixfurther six

gas discoveries. gas discoveries. One oil and four gas discoveries have been made in the South One oil and four gas discoveries have been made in the South

African part of the Orange Basin.African part of the Orange Basin.

Petroleum Systems and Petroleum Systems and PlaysPlays

Exploration to-date has confirmed that several petroleum systems sourced Exploration to-date has confirmed that several petroleum systems sourced from known source rocks are at work in the Orange Basin. from known source rocks are at work in the Orange Basin.

contain a number of exploration plays and prospects which are currently contain a number of exploration plays and prospects which are currently being pursued by various international oil companies.being pursued by various international oil companies.

Only Only 30 wells30 wells were drilled in this vast repository off South Africa. were drilled in this vast repository off South Africa. The main play elements are shown on figure 16. The main play elements are shown on figure 16.

Forest Oil are pursuing the Albian Gas Play, the Upper Cretaceous Shallow Gas Forest Oil are pursuing the Albian Gas Play, the Upper Cretaceous Shallow Gas Play, the Barremian Deep Gas Play and the Synrift Oil Play in the shelfal portion Play, the Barremian Deep Gas Play and the Synrift Oil Play in the shelfal portion of blocks 1 and 2; and the Upper Cretaceous Deep-water Slope Turbidite of blocks 1 and 2; and the Upper Cretaceous Deep-water Slope Turbidite Oil/Gas Play in block 2.Oil/Gas Play in block 2.

Sasol Petroleum International are pursuing the Barremian Pinch-out Gas Play in Sasol Petroleum International are pursuing the Barremian Pinch-out Gas Play in block 3A/4A.block 3A/4A.

Global Energy Holdings are pursuing the Upper Cretaceous Deep-water Global Energy Holdings are pursuing the Upper Cretaceous Deep-water Turbidite Oil Play in block 3B/4B. Interest in block 5 is also being evaluated.Turbidite Oil Play in block 3B/4B. Interest in block 5 is also being evaluated.

The strongest petroleum system discovered to-date is the natural gas The strongest petroleum system discovered to-date is the natural gas system sourced from the lower Aptian and Barremian source shales system sourced from the lower Aptian and Barremian source shales located in the depocentre of the Orange Basin.located in the depocentre of the Orange Basin.

The Albian Gas Play within this system has yielded the A-K (Ibubezi) gas The Albian Gas Play within this system has yielded the A-K (Ibubezi) gas field currently being appraised by Forest Oil. field currently being appraised by Forest Oil.

The reservoirs are stratigraphically trapped fluvial channel-fill The reservoirs are stratigraphically trapped fluvial channel-fill sandstones, which yielded 68 MMSCFG/d and 340 barrels of condensate sandstones, which yielded 68 MMSCFG/d and 340 barrels of condensate per day during the testing of the A-K1 discovery well by Soekor in 1987. per day during the testing of the A-K1 discovery well by Soekor in 1987.

The Barremian Deep Gas Play has yielded the Kudu gas field in the The Barremian Deep Gas Play has yielded the Kudu gas field in the Orange Basin off southern Namibia which is presently being appraised by Orange Basin off southern Namibia which is presently being appraised by Shell. Shell.

The reservoirs are stratigraphically trapped aeolian sandstones with good The reservoirs are stratigraphically trapped aeolian sandstones with good gas deliverability. gas deliverability.

Oil SystemsOil Systems

The only oil system confirmed to-The only oil system confirmed to-date occurs in the isolated A-J half-date occurs in the isolated A-J half-graben within the synrift graben within the synrift succession.succession.

The oil is sourced from typically The oil is sourced from typically rich Hauterivian lacustrine shales rich Hauterivian lacustrine shales within the half-graben and is within the half-graben and is trapped stratigraphically within trapped stratigraphically within lake shore-line sandstones lake shore-line sandstones interbedded with the source interbedded with the source shales. shales.

The maximum flow rate reached The maximum flow rate reached whilst testing is about 200 barrels whilst testing is about 200 barrels per day of viscous oil. per day of viscous oil.

This geological success has shown This geological success has shown the potential of the Synrift Oil Play.the potential of the Synrift Oil Play.

Several speculative petroleum Several speculative petroleum systems and plays are also systems and plays are also prognosed in the undrilled parts of prognosed in the undrilled parts of the basin, notably in the deep the basin, notably in the deep water areas.water areas.