Presentation on theme: "Geology of Petroleum Systems"— Presentation transcript:
1 Geology of Petroleum Systems In order to have a commercial hydrocarbon prospect, several requirement must be met. There must be (1) a hydrocarbon source, (2) a reservoir rock, and (3) a trap, Moreover, the relative time at which these features developed is important. The systematic assessment of these parameter and their affect on hydrocarbon occurrence is known as a Petroleum Systems approach to oil and gas evaluation.
2 Geology of Petroleum Systems 2 Petroleum GeologyGeology of Petroleum Systems 2Objectives are to be able to:Discuss basic elements of Petroleum SystemsDescribe plate tectonics and sedimentary basinsRecognize names of major sedimentary rock typesDescribe importance of sedimentary environments to petroleum industryDescribe the origin of petroleumIdentify hydrocarbon trap typesDefine and describe the important geologic controls on reservoir properties, porosity and permeability
3 Geology of Petroleum Systems 3 OutlineGeology of Petroleum Systems 3Petroleum Systems approachGeologic Principles and geologic timeRock and minerals, rock cycle, reservoir propertiesHydrocarbon origin, migration and accumulationSedimentary environments and facies; stratigraphic trapsPlate tectonics, basin development, structural geologyStructural traps
4 Geology of Petroleum Systems 4 Petroleum System - A DefinitionA 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)
5 Geology of Petroleum Systems 5 Cross Section Of A Petroleum SystemGeology of Petroleum Systems 5(Foreland Basin Example)Geographic Extent of Petroleum SystemExtent of PlayExtent of Prospect/FieldOOOStratigraphicExtent ofPetroleumOverburden RockSystemEssentialElementsSeal RockofReservoir RockThis cross section shows the elements of a Petroleum System. Potential reservoir sandstones (yellow), deposited at the basin margin, intertongue to the left with organic-rich source rocks. Owing to the increasing temperature with depth, the source rocks are mature for gas in the deep basin. Below the oil window, the source rocks are generating oil. Hydrocarbons migrate up the flank of the basin and accumulate in a trap (structural). The layer overlying the reservoir is a low-permeability seal. In order to have a commercial field/ prospect, the trap must form prior to hydrocarbon migration, and the trap must have maintained its integrity.Basin FillPetroleumSedimentaryPod of ActiveSystemSource RockSource RockUnderburden RockPetroleum Reservoir (O)Basement RockFold-and-Thrust BeltTop Oil Window(arrows indicate relative fault motion)Top Gas Window(modified from Magoon and Dow, 1994)
6 Basic Geologic Principles Geology of Petroleum Systems 6Basic Geologic PrinciplesUniformitarianismOriginal HorizontalitySuperpositionCross-Cutting RelationshipsThe following are basic principles or laws are used to evaluate the relative ages and the relations among rock layers.Uniformitarianism - “The present is the key to the past.” By studying modern geologic processes, we can interpret past geologic events and rock-forming processes.Original Horizonality - “Sedimentary layers are deposited in a horizontal or nearly horizontal position.” If sedimentary layers are tilted or folded, they have been subjected to deforming stresses.Superposition - “Younger sedimentary beds occur on top of older beds, unless they have been overturned or faulted.”Cross-Cutting Relations - “Any geologic feature that cuts another geologic feature is younger than the feature that it cuts.”
7 Cross-Cutting Relationships Geology of Petroleum Systems 7KJIHGAngular UnconformityCELaw of cross-cutting relationships. In the figure above, the igneous dike (F) is younger than layers A-E but older than layer G, because a geologic feature is younger than any other geologic feature that it cuts. This is an important law for determining the relative ages of geologic features. According to the “Law of Superposition,” layer “I” is older than layer “J,” and the rocks beneath the unconformity are older from left to right. From the “Principle of Original Horizonality,” we infer that layers “A” through “F” have been deformed.FDIgneousDikeBIgneous SillA
8 Types of Unconformities Geology of Petroleum Systems 8Types of UnconformitiesDisconformityAn unconformity in which the beds above and below are parallelAngular UnconformityAn unconformity in which the older bed intersect the younger beds at an angleNonconformityAn unconformity in which younger sedimentary rocks overlie older metamorphic or intrusive igneous rocksSedimentary rock are deposited in successive layers that record the history of their time, much like the pages in history book. However, the rock record is never complete. Missing layers (gaps in time) result in unconformities. An unconformity is a surface of non-deposition or erosion that separates younger rocks from older rocks. The previous slide shows an angular unconformity.
9 Geology of Petroleum Systems 9 CorrelationGeology of Petroleum Systems 9Establishes the age equivalence of rock layers in different areasMethods:Similar lithologySimilar stratigraphic sectionIndex fossilsFossil assemblagesRadioactive age datingCorrelation is the process of relating rocks in terms of their ages. It is one of the most important task in petroleum geology. Correlation may involve rock layers studied at outcrops, in well logs, in seismic data, or in some combination of these occurrences.
10 Geology of Petroleum Systems 10 Geologic Time ChartEonEraPeriodEpochQuaternaryRecentQuaternaryperiodPleistocenePhanerozoicTertiaryPliocene50101Miocene100Cretaceous20MesozoicCenozoic EraTertiaryperiodBillions of years ago2150Millions of years agoJurassic30Oligocene(Precambrian)CryptozoicMillions of years ago200Triassic40Eocene3250Permian50PennsylvanianPaleocene430060Mississippian4.6350Initially, the geologic time scale was developed on the basis of relative geologic ages, using fossil assemblages and the laws of superposition, cross-cutting relations, etc. Subsequently, absolute ages were assigned to the time scale on the basis of radioactive dating.Devonian400PaleozoicSilurian450Ordovician500550Cambrian600
11 Geology of Petroleum Systems 11 RocksThe earth’s crust or outer shell is composed mainly of rocks. A rock is defined as “an aggregate of one or more minerals.” The three major rock types, based on their origin, are igneous, metamorphic, and sedimentary. Petroleum Systems and most oil and gas production occur in sedimentary rocks, which form a thin veneer on the surface of the earth’s crust.
12 Classification of Rocks Geology of Petroleum Systems 12IGNEOUSSEDIMENTARYMETAMORPHICRock-formingprocessSource ofmaterialMolten materials indeep crust andupper mantleWeathering anderosion of rocksexposed at surfaceRocks under hightemperaturesand pressures indeep crustThe three major rock types are sedimentary, igneous, and metamorphic rocks. Their classification is based on their origins.Sedimentary rocks are formed from particles derived from igneous, metamorphic or other sedimentary rocks by weathering and erosion. Sedimentary rocks provide the hydrocarbon source rocks and most of the oil and gas reservoir rocks.Igneous rocks are formed from molten material which is either ejected from the earth during volcanic activity (e.g., lava flows, and ash falls), or which crystallizes from a magma that is injected into existing rock and cools slowly, giving rise rocks such as granites. Igneous rocks are of minor importance for oil exploration. Rarely, hydrocarbon is produced from fractured igneous rocks.Metamorphic rocks are formed by subjecting any of the three rock types to high temperatures and pressures, that alter the character of the existing rock. Common examples of metamorphic rocks are marble derived from limestone and slate derived from shale. Due to the high temperature and pressures there is very little organic matter or hydrocarbons in metamorphic rocks.Crystallization(Solidification of melt)Sedimentation, burialand lithificationRecrystallization due toheat, pressure, orchemically active fluids
13 Geology of Petroleum Systems 13 The Rock CycleMagmaMetamorphicRockSedimentaryIgneousSedimentHeat and PressureWeathering,Transportationand DepositionWeathering, Transportation,ColingadSfctMe(rysz)HAPumphW,TDLGeology of Petroleum Systems 13The rocks of the earth’s crust are constantly being recycled. Magna solidifies to form igneous rocks. If igneous rock are exposed at the surface, they weather, and weathered rock fragments are transported and sediment, deposited, and lithified into sedimentary rocks. If the igneous or sedimentary rocks are subjected to temperatures and pressures that exceed those under which they solidified, they may undergo changes to form metamorphic rocks.
14 Sedimentary Rock Types Geology of Petroleum Systems 14Sedimentary Rock TypesRelative abundanceSandstoneand conglomerate~11%Siltstone, mudand shale~75%Limestone anddolomite~13%This slide shows the relative abundance of the major sedimentary rock types. These rocks comprise approximately 99% of all sedimentary rocks, including hydrocarbon source rocks and traps. Sedimentary rock can be divided into two major classes.CLASTICS- Sandstone, conglomerate, siltstone, and shale- Comprised mainly of silicate minerals- Classified on the basis of grain size and mineral compositionCARBONATES- limestone and dolomite- consist mainly of the carbonate minerals calcite(limestone) or dolomite (dolostone)
15 Geology of Petroleum Systems 15 Minerals - DefinitionGeology of Petroleum Systems 15Naturally OccurringSolidGenerally Formed byInorganic ProcessesOrdered InternalArrangement of Atoms(Crystal Structure)Minerals are the basic building blocks of all rocks. The types of minerals present in a rock influence its chemical stability, and thus, its suitability as a reservoir.Chemical Compositionand Physical PropertiesFixed or Vary WithinQuartz CrystalsA Definite Range
16 Average Detrital Mineral Composition of Shale and Sandstone Geology of Petroleum Systems 16Mineral CompositionShale (%)Sandstone (%)Clay Minerals605Quartz3065Feldspar410-15Rock Fragments<515The composition of the detrital (broken) rock fragments in a sandstone or shale varies, because it depends on the type(s) of rock that weathered to form the fragments and the climate. Therefore, the table above represents only averages.Carbonate3<1Organic Matter,<3<1Hematite, andOther Minerals(modified from Blatt, 1982)
17 Geology of Petroleum Systems 17 The Physical and Chemical Characteristics of Minerals Strongly Influence the Composition of Sedimentary RocksQuartzMechanically and Chemically StableCan Survive Transport and BurialFeldsparNearly as Hard as Quartz, butCleavage Lessens Mechanical StabilityMay be Chemically Unstable in SomeClimates and During BurialQuartz, feldspar, calcite, and various clay minerals are among the primary minerals present in sedimentary rocks.CalciteMechanically Unstable During TransportChemically Unstable in Humid ClimatesBecause of Low Hardness, Cleavage, andReactivity With Weak Acid
18 Geology of Petroleum Systems 18 Some Common MineralsOxidesSulfidesCarbonatesSulfatesHalidesAragoniteHematitePyriteAnhydriteHaliteGalenaCalciteGypsumSylviteMagnetiteSphaleriteDolomiteFe-DolomiteAnkeriteSilicatesNon-FerromagnesianFerromagnesian(Common in Sedimentary Rocks)(not common in sedimentary rocks)QuartzOlivineMuscovite (mica)The non-feromagnesian silicate minerals, on the left, are more common in sedimentary rocks than are feromagnesian minerals, which are chemically less stable.PyroxeneFeldsparsAugitePotassium feldspar (K-spar)AmphiboleOrthoclaseHornblendeMicrocline, etc.Biotite (mica)PlagioclaseAlbite (Na-rich - common) throughRed = Sedimentary Rock-Anorthite (Ca-rich - not common)Forming Minerals
19 The Four Major Components Geology of Petroleum Systems 19FrameworkSand (and Silt) Size Detrital GrainsMatrixClay Size Detrital MaterialCementMaterial precipitated post-depositionally, during burial. Cements fill pores and replace framework grainsPoresVoids between above componentsSandstones are the most common clastic reservoir rocks. They are composed of a framework of coarse grains that may surrounded by finer fragments called matrix. After framework and matrix sediments are deposited, they may be held together by a chemically precipitated cement. Pores are any voids that remain after framework and matrix are cemented; they are the areas occupied by oil or gas in a hydrocarbon reservoir and water elsewhere.
20 Sandstone Composition Framework Grains Geology of Petroleum Systems 20KF = PotassiumFeldsparPRF = Plutonic RockFragmentPRFKFP = PoreCEMENTThis photomicrograph highlights three of the four major components of a sedimentary rock, framework grains, cement, and pores. KF and PRF are types of framework grains. Plutonic rock fragments are derived from igneous rocks, such as granite.Potassium Feldspar isStained Yellow With aChemical DyePPores are ImpregnatedWith Blue-Dyed EpoxyNorphlet Sandstone, Offshore Alabama, USAGrains are About =< 0.25 mm in Diameter/Length
21 Geology of Petroleum Systems 21 Porosity in SandstoneGeology of Petroleum Systems 21PoreThroatPores Provide theVolume to ContainHydrocarbon FluidsPore Throats RestrictFluid FlowA pore throat is the narrow passage that connects adjacent pores. Because they are smaller than pores, they limit flow. They may further restrict flow if they become blocked by migrating fine particles, such as clays.Porosity of the reservoir is of great importance in determining the volume of original hydrocarbons in-place. Generally, porosity in sandstones decreases with depth, owing to compaction, cementation, etc. Porosity of sandstones commonly ranges from 1 to 30%.Porosity (ø) = (total pore volume / bulk volume) 100Effective porosity = (interconnected pore volume / bulk volume) 100Permeability (k, or coefficient of proportionality) is a measure of the ability of a rock to transmit fluid. Darcy’s law states that the rate (q) at which a fluid moves through a cross section of a rock varies inversely with viscosity (µ) and directly with the pressure gradient (dp / dx) in the direction of flow.Darcy’s Law: q = (k/µ)(dp/dx)Although the unit of measure for permeability is the Darcy, many rocks have permeabilities than much lower than 1 Darcy, so permeability may be reported in millidarcies (md).Scanning Electron MicrographNorphlet Formation, Offshore Alabama, USA
22 Geology of Petroleum Systems 22 Clay Minerals in Sandstone Reservoirs Fibrous Authigenic IlliteGeology of Petroleum Systems 22Secondary Electron MicrographSignificantPermeabilityReductionNegligiblePorosityIlliteReductionHigh IrreducibleIllite in reservoirs typically occurs as sub-micron diameter fibers.Illite is important in petroleum geology, because illite fibers can block pore throats, significantly reducing porosity.Fibrous illite is may not be recognized in samples from cores that have been air dried. The drying process may cause the delicate fibers collapse against grain surfaces. Thus, permeability measurements taken from authigenic illite-bearing core samples may be in error.As shown in the scanning electron photomicrograph above, fibrous illite can be preserved if cores are collected using special techniques to preserve reservoir fluids.Water SaturationMigration ofFines ProblemJurassic Norphlet SandstoneHatters Pond Field, Alabama, USA(Photograph by R.L. Kugler)
23 Geology of Petroleum Systems 23 Clay Minerals in Sandstone Reservoirs Authigenic ChloriteGeology of Petroleum Systems 23Secondary Electron MicrographIron-RichVarieties ReactWith AcidOccurs in SeveralDeeply BuriedSandstones WithHigh ReservoirAuthigenic chlorite in sandstone reservoirs typically is Fe-rich.This iron-rich chlorite may react with acid used during reservoir stimulation. This reaction results in the formation of gelatinous blobs that have large diameters relative to pore throat sizes. Thus, permeability may be reduced by gelatinous blobs that block pore throats.Some deeply buried (>20,000 feet) sandstone reservoirs containing authigenic chlorite grain coats have anomalously high porosity (may exceed of 20%). Examples of deeply buried, chlorite-cemented sandstone with high reservoir quality include the Tuscaloosa and Norphlet sandstones in the U.S. Gulf Coast.QualityOccurs as ThinCoats on DetritalGrain SurfacesJurassic Norphlet Sandstone~ 10mmOffshore Alabama, USA(Photograph by R.L. Kugler)
24 Geology of Petroleum Systems 24 Clay Minerals in Sandstone Reservoirs Authigenic KaoliniteGeology of Petroleum Systems 24Secondary Electron MicrographSignificant PermeabilityReductionHigh Irreducible WaterSaturationKaolinite may fill pores or replace detrital grains, such as feldspar.Kaolinite is relatively inert and does not react with fluids that may be introduced into the reservoir.However, kaolinite platelets have large diameters relative to pore throats. As a result, under certain reservoir, kaolinite may migrate to and block pore throats, thus reducing permeability.Kaolinite also contains water in micropores between platelets and stacks of platelets. The presence of this water in kaolinite-bearing sandstone must be acknowledged during well-log analysis to proper interpretation of water saturation.Migration of FinesProblemCarter SandstoneNorth Blowhorn Creek Oil UnitBlack Warrior Basin, Alabama, USA(Photograph by R.L. Kugler)
25 Effects of Clays on Reservoir Quality Geology of Petroleum Systems 251001010.10.011000261418Permeability (md)Porosity (%)Authigenic IlliteAuthigenic Chlorite(modified from Kugler and McHugh, 1990)Note the significantly lower permeability in the sandstone containing illite cement.Porosity and permeability are higher in the chlorite cemented sandstone.This example is from deep (18,000 to >20,000 feet)Norphlet sandstone reservoirs in onshore Alabama (illite cement) and offshore Alabama (chlorite cement), USA.
26 Influence of Clay-Mineral Distribution on Effective Porosity Geology of Petroleum Systems 26fClayeMineralsDispersed ClayDetrital QuartzGrainsfeClay LaminationThe mode of clay occurrence effects reservoir performance and must be considered in petrophysical interpretations.fStructural Claye(Rock Fragments,Rip-Up Clasts,Clay-Replaced Grains)
27 Geology of Petroleum Systems 27 DiagenesisGeology of Petroleum Systems 27Diagenesis is the Post-Depositional Chemical andMechanical Changes thatCarbonateOccur in Sedimentary RocksCementedSome Diagenetic Effects IncludeOilCompactionStainedPrecipitation of CementDissolution of FrameworkThe term diagenesis refers to “the chemical and mechanical changes that occur in sediments after they are deposited.” Although most diagenetic changes degrade reservoir quality, some diagenetic effects , such as dissolution, may enhance reservoir quality.Grains and CementThe Effects of Diagenesis MayEnhance or Degrade ReservoirQualityWhole CoreMisoa Formation, Venezuela
28 Fluids Affecting Diagenesis Geology of Petroleum Systems 28PrecipitationSubsidenceCH4,CO2,HSPetroleumFluidsMeteoricWaterCOMPACTIONALWATERChannelFlowEvapotranspirationEvaporationInfiltrationWater TableZone of abnormal pressureIsothermsAtmosphericCirculation(modified from from Galloway and Hobday, 1983)As sediments are buried, the fluid and pressure systems of the basin evolve and the temperature increases. Also, ground water (meteoric) systems develop at the basin flanks. Diagenesis occurs as minerals in the sedimentary rock equilibrate to these new physical conditions and fluid chemistry.
29 Geology of Petroleum Systems 29 Dissolution PorosityGeology of Petroleum Systems 29Thin Section Micrograph - Plane Polarized LightAvile Sandstone, Neuquen Basin, ArgentinaDissolution ofFramework Grains(Feldspar, forExample) andCement mayEnhance theInterconnectedPore SystemThis is CalledSecondary PorosityPoreQuartz DetritalGrainPartiallyDissolvedFeldsparDiagenesis may enhance porosity. The thin section micrograph above shows a partially dissolved feldspar grain in a reservoir sandstone.Feldspar detrital grains and calcite cement most commonly dissolve in sandstone to produce secondary porosity.Engineers may the term “secondary porosity” in a different context to refer to fractures.Secondary framework grain (or cement) dissolution may form early in the burial history of a sandstone.However, secondary porosity formed during late burial significantly enhances the pore system of many reservoirs.(Photomicrograph by R.L. Kugler)
30 Hydrocarbon Generation, Migration, and Accumulation Geology of Petroleum Systems 30Hydrocarbon Generation, Migration, and AccumulationHydrocarbon generation and migration occur primarily during burial, diagenesis, and catagenesis. As sediments are buried, temperature and pressure increase, and kerogens (organic rock fragments) undergo chemical and physical changes that result in formation of oil and gas and excess formation pressure. From the deep basin, hydrocarbons migrate up the flank until they encounter traps or avenue find escape routes to the surface. Understanding the processes involved in hydrocarbon origin and migration is important in assessing exploration potential of a region.
31 Geology of Petroleum Systems 31 Organic Matter in Sedimentary RocksKerogenDisseminated Organic Matter inSedimentary Rocks That is Insolublein Oxidizing Acids, Bases, andVitriniteOrganic Solvents.VitriniteA nonfluorescent type of organic materialin petroleum source rocks derivedprimarily from woody material.The organic fragments in sedimentary rocks are called kerogen. There are different types of kerogen, depending on the source of organic material. Type I and Type II kerogens, which form mainly oil, come primarily from small marine organisms, whereas Type III kerogens come from plant materials and are gas prone. If sedimentary rocks have sufficient organic content to supply economic hydrocarbon deposits, they are called source rocks. Most source rocks are shale or carbonates rocks that were deposited under anaerobic conditions.The reflectivity of vitrinite is one of thebest indicators of coal rank and thermalmaturity of petroleum source rock.Reflected-Light Micrographof Coal
32 Geology of Petroleum Systems 32 Interpretation of Total Organic Carbon (TOC) (based on early oil window maturity)HydrocarbonTOC in ShaleTOC in CarbonatesGeneration(wt. %)(wt. %)PotentialPoorFairThe viability of shales and carbonates as source rocks depends on the weight of organic content and the layer thickness. Note the different values for shale and carbonate rocks in each category.GoodVery GoodExcellent>5.0>2.0
33 Geology of Petroleum Systems 33 Schematic Representation of the Mechanism of Petroleum Generation and Destruction(modified from Tissot and Welte, 1984)Organic DebrisKerogenCarbonInitial BitumenOil and GasMethaneOil ReservoirMigrationThermal DegradationCrackingDiagenesisCatagenesisMetagenesisProgressive Burial and HeatingDiagenetic hydrocarbon formation occurs at shallow depths and relatively low formation temperatures. During catagenesis, oil and wet gas forms, followed by dry gas and the cracking of heavy hydrocarbons. When the metagenesis occurs, all heavy hydrocarbons have been cracked, and methane and carbon are the end products.
34 Geology of Petroleum Systems 34 Comparison of Several Commonly Used Maturity Techniques and Their Correlation to Oil and Gas Generation LimitsIncipient Oil GenerationMax. Oil GeneratedOil FloorWet Gas FloorDry Gas FloorMax. Dry GasGenerated(modified from Foster and Beaumont, 1991, after Dow and O’Conner, 1982)Vitrinite Reflectance (Ro) %Weight % Carbon in KerogenSpore Coloration Index (SCI)Pyrolysis T(C)max0.20.30.40.54.03.02.01.3123456789104304504656570758085909184.108.40.206.91.01.2OILWetGasDryRelation of thermal maturity to hydrocarbon generation. Various thermal maturation indices may be used to assess the thermal maturity of source rocks and the remaining hydrocarbon potential.
35 Generation, Migration, and Trapping of Hydrocarbons Geology of Petroleum Systems 35Generation, Migration, and Trapping of HydrocarbonsFault(impermeable)Oil/watercontact (OWC)Hydrocarbonaccumulationin thereservoir rockMigration routeSealSeveral conditions must be satisfied for an economic hydrocarbon accumulation to exist. First, there must be sedimentary rocks that have good source rock characteristics and have reached thermal maturity. Second, the hydrocarbons must have migrated from the source rock to a potential reservoir, which must have adequate porosity and permeability. Finally, there must be a trap to arrest the hydrocarbon migration and hold sufficient quantities to make the prospect economic. Hydrocarbon traps usually consist of an impervious layer (seal), such as shale, above the reservoir and barrier such as a fault or facies pinch that terminates the reservoir.ReservoirrockTop of maturitySource rock
36 Geology of Petroleum Systems 36 Cross Section Of A Petroleum SystemGeology of Petroleum Systems 36(Foreland Basin Example)Geographic Extent of Petroleum SystemExtent of PlayExtent of Prospect/FieldOOOStratigraphicExtent ofPetroleumOverburden RockSystemEssentialElementsSeal RockofReservoir RockCross section showing the elements of a Petroleum System. Potential reservoir sandstones (yellow), deposited at the basin margin, intertongue to the left with organic-rich source rocks. Owing to the increasing temperature with depth, the source rocks are mature for gas in the deep basin. Below the oil window, the source rocks are generating oil. Hydrocarbons migrate up the flank of the basin and accumulate in a structural trap. In order to have a commercial field/ prospect, the trap must form before hydrocarbon migration occurs.Basin FillPetroleumSedimentaryPod of ActiveSystemSource RockSource RockUnderburden RockPetroleum Reservoir (O)Basement RockFold-and-Thrust BeltTop Oil Window(arrows indicate relative fault motion)Top Gas Window(modified from Magoon and Dow, 1994)
37 Geology of Petroleum Systems 37 Hydrocarbon TrapsStructural trapsStratigraphic trapsCombination trapsStructural traps are caused by structural features. They are usually formed as a result of tectonics.Stratigraphic traps are usually caused by changes in rock quality.Combination traps that combine more than one type of trap are common in petroleum reservoirs.Other types of traps (such as hydrodynamic traps) are usually less common.
38 Geology of Petroleum Systems 38 Structural Hydrocarbon TrapsGeology of Petroleum Systems 38GasOilShaleTrapFracture BasementClosureOil/GasContactOil/WaterContactSealOilFold TrapSaltDiapirSaltDomeOil(modified from Bjorlykke, 1989)
39 Geology of Petroleum Systems 39 Hydrocarbon Traps - DomeGasOilWaterThe dome above shows gravity separation of fluids. Shale comprises the upper and lower confining beds.SandstoneShale
40 Geology of Petroleum Systems 40 Fault TrapOil / GasSandShaleIn this normal fault trap, oil-bearing sandstone is juxtaposed against impervious shale.
41 Geology of Petroleum Systems 41 Stratigraphic Hydrocarbon TrapsGeology of Petroleum Systems 41UnconformityPinch outOil/GasUncomformityOil/GasChannel Pinch OutStratigraphic hydrocarbon traps occur where reservoir facies pinch into impervious rock such as shale, or where they have been truncated by erosion and capped by impervious layers above an unconformity.Oil/Gas(modified from Bjorlykke, 1989)
42 Geology of Petroleum Systems 42 Other TrapsMeteoricWaterAsphalt TrapBiodegradedOil/AsphaltPartlyBiodegraded OilWaterHydrodynamic TrapHydrostaticHeadIn hydrodynamic traps, the hydrocarbon is trapped by the action of water movements. Tilted contacts are common in this case. The water usually comes from a source such as rain falls or rivers.ShaleWaterOil(modified from Bjorlykke, 1989)
44 Geology of Petroleum Systems 44 Reservoir Heterogeneity in SandstoneHeterogeneity MayResult From:Depositional FeaturesDiagenetic Features(Whole Core Photograph, MisoaSandstone, Venezuela)HeterogeneitySegments ReservoirsIncreases Tortuosity ofFluid Flow
45 Geology of Petroleum Systems 45 Reservoir Heterogeneity in SandstoneHeterogeneity Also MayResult From:FaultsFracturesFaults and Fractures maybe Open (Conduits) orClosed (Barriers) to FluidFlow(Whole Core Photograph, MisoaSandstone, Venezuela)
46 Geology of Petroleum Systems 46 Geologic Reservoir HeterogeneityBoundingSurfaceBoundingSurfaceExamples of eolian sandstone reservoirs include the Nugget sandstone in the Rocky Mountain region, the Norphlet sandstone in the U.S. Gulf Coast, and the Rottliegend sandstone in the North Sea.Eolian Sandstone, Entrada Formation, Utah, USA
47 Geology of Petroleum Systems 47 Scales of Geological Reservoir HeterogeneityField WideInterwellWell-Bore(modifiedfromWeber, 1986)Hand Lens orBinocular MicroscopeUnaided EyePetrographic orScanning ElectronMicroscopeDeterminedFrom Well Logs,Seismic Lines,StatisticalModeling,etc.10-100'smmm1-10's100's10's1-10 km100's mWellInterwellAreaReservoirSandstoneThe tools and techniques we use to characterize the reservoir have different scales.
48 Geology of Petroleum Systems 48 Scales of Investigation Used inReservoir CharacterizationGigascopicMegascopicMacroscopicMicroscopicWell TestReservoir ModelGrid CellWireline LogIntervalCore PlugGeologicalThin SectionRelative Volume110142 x 10123 x 1075 x 102300 m50 m5 m150 m2 m1 mcmmm -m(modified from Hurst, 1993)
49 Geology of Petroleum Systems 49 Stages In The Generation ofAn Integrated Geological Reservoir ModelLog AnalysisWell Test AnalysisCore AnalysisRegional GeologicFrameworkDepositionalModelDiageneticIntegratedGeologic ModelApplications StudiesModel TestingAnd RevisionStructuralFluid(As Needed)Geologic ActivitiesReserves EstimationSimulation