Book contents
- Frontmatter
- Contents
- Preface
- Acknowledgments
- I Fundamentals of thrustbelts
- II Evolving structural architecture and fluid flow
- III Thermal regime
- IV Petroleum systems
- 17 Hydrocarbons in thrustbelts: global view
- 18 Source rocks in thrustbelt settings
- 19 Maturation and migration in thrustbelts
- 20 Seals and traps in thrustbelts
- 21 Reservoir destruction or enhancement due to thrusting
- 22 Remaining petroleum potential of thrustbelts
- References
- Index
18 - Source rocks in thrustbelt settings
Published online by Cambridge University Press: 23 December 2009
- Frontmatter
- Contents
- Preface
- Acknowledgments
- I Fundamentals of thrustbelts
- II Evolving structural architecture and fluid flow
- III Thermal regime
- IV Petroleum systems
- 17 Hydrocarbons in thrustbelts: global view
- 18 Source rocks in thrustbelt settings
- 19 Maturation and migration in thrustbelts
- 20 Seals and traps in thrustbelts
- 21 Reservoir destruction or enhancement due to thrusting
- 22 Remaining petroleum potential of thrustbelts
- References
- Index
Summary
General features of source rocks
Any petroleum system, whether or not in a thrustbelt setting, requires a source rock to be present in the sedimentary section. Without the strata containing at least 0.5–1.0% preserved organic matter, there can be no hydrocarbon charge. Oil and gas form by the thermal breakdown of buried specific organic matter; oil in the temperature range 110–150 °C and natural gas in the temperature range 140–250 °C. However, organic matter starts to undergo chemical alteration from the instant of death of the precursor organism. It progresses from a living organism through a process of diagenesis, to hydrocarbons through catagenesis and finally to a carbon residue through thermal conversion, i.e. metagenesis (Fig. 18.1).
Photosynthesizing aerobic and anaerobic plants and microorganisms convert atmospheric carbon dioxide to organic compounds. Most of these molecules become energy sources that the plants and their predators are able to almost completely break down, converting them back into CO2 by the process of respiration, thus closing the carbon cycle. Only a very small proportion of organic matter escapes decomposition and is buried in sediments (Hunt, 1979). This proportion represents less than 0.1% by volume of primary productivity and can be considered as a ‘leak’ in the carbon cycle. This is the organic matter that may eventually be converted to fossil fuels after further burial.
The nature of the organic matter in the source rock and the nature of the initially derived hydrocarbon products are a function of both the precursor organic matter and the depositional environment. The source material for fossil hydrocarbons is derived from four chemically distinct classes of matter: lipids, amino acids, carbohydrates and lignins (Tissot and Welte, 1984; Berkowitz, 1997).
- Type
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- Information
- ThrustbeltsStructural Architecture, Thermal Regimes and Petroleum Systems, pp. 385 - 398Publisher: Cambridge University PressPrint publication year: 2005