mk pgeochem 2
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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