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Lesson – 2

Edi B. SetyobudiProdi Teknik Geologi

Universitas Diponegoro

Introduction to PetroleumGeochemistry

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Further ReadingsHorsfield, B. and J. Rullkötter, 1994, “Diagenesis,Catagenesis and Metagenesis of Organic Matter”, inThe Petroleum System – From Source to Trap, AAPGMemoir 60

Chilingar, G.V. et al , 2005, “Geology andGeochemistry of Oil and Gas”. Chapter 9

Verweij, J.M. 1993, “Hydrocarbon Migration Systems

Analysis”, Chapters 3, 4 and 5Wenger,L.M., C.L. Davis and G.H. Isaksen, 2002,“Multiple Controls on Petroleum Biodegradation andImpact on Oil Quality”, SPE Paper

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ObjectivesPrinciples of hydrocarbongeneration, migration, accumulation

and alterationBasics of ‘oil to oil’ and ‘oil to sourcerock’ correlations

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Problems with Source Rock Evaluation

Most of drilling depths above mature windows

Penetrated sections may be of different facies

Often extrapolation necessary assisted bymodeling

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Geochemical Log

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Example of Basin Modeling

Input - stratigraphy, geochemistry andheat flowOutput – maturation window, amount ofHC generated and timing of m tur tion

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PrimaryMigration –

expulsionof HC outof sourcerock

SecondaryMigration – HCmovementalong carierbed

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Primary Migration Controversy

Primary migration isleast understood

Oil generated at great

depthShale porosity very lowat that depth

How would HC move insuch low porosity

Some ideas have beenproposed

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Primary Migration

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Video - Migration

After expulsion

Bouyancy

Seal /impermeablelayer

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Secondary Migration

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Trap Filling

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MigrationPathway Map

The map must bedatumed at ahorizon as close

as possible to thetiming ofmaturation

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Differential Entrapment

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Differential Entrapment

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HC Alterations

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HC Alterations

Water Washing – soluble components removeddue to contact with waterPhase Separation – gas and lighter componentsescape from the trap due to partial leakage (faultsor incompetent seals)Gas De-Asphalting – asphalt precipitation due togas entering an oil reservoirThermal Cracking – reservoir exposed to higher

temperature due to deep burial makes heaviercomponents to crack into lighter HCBiodegradation – bacteria eating some HCcomponents causing oil degradation

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Biodegradation

Meteoric water influx brings oxygen andbacteria into reservoir

Aerobic and Anaerobic bacteria

H2S may be generated due to sulfate-reducing bacteria

Temperature below 80o

C (175o

F) andheavy biodegradation occurs below50 oC (120 oF)

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Gas Chromatograms ofBiodegraded Oils

UCM – Unresolved Complex Mixture

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Questions & Answers