Kerogen
| Exploring for Oil and Gas Traps | |
| |
| Series | Treatise in Petroleum Geology |
|---|---|
| Part | Critical elements of the petroleum system |
| Chapter | Evaluating source rocks |
| Author | Carol A. Law |
| Link | Web page |
| Store | AAPG Store |
Depositional environment is the dominant factor in determining the types of organic matter found in a rock. Only two types of organic matter are found in rocks: land derived and aquatic algae derived. Heat and pressure convert organic matter into a substance called humin and then into kerogen. Time and temperature convert kerogen into petroleum.
What is kerogen?
Geochemists[1][2] define kerogen as the fraction of sedimentary organic constituent of sedimentary rocks that is insoluble in the usual organic solvents. Kerogens are composed of a variety of organic materials, including algae, pollen, wood, vitrinite, and structureless material. The types of kerogens present in a rock largely control the type of hydrocarbons generated in that rock. Different types of kerogen contain different amounts of hydrogen relative to carbon and oxygen. The hydrogen content of kerogen is the controlling factor for oil vs. gas yields from the primary hydrocarbon-generating reactions.
Kerogen quality
The type of kerogen present determines source rock quality. The more oil prone a kerogen, the higher its quality. Four basic types of kerogen are found in sedimentary rocks. A single type or a mixture of types may be present in a source rock. The table below lists and defines these four basic kerogen types.
| Kerogen type | Predominant hydrocarbon potential | Amount of hydrogen | Typical depositional environment |
|---|---|---|---|
| I | Oil prone | Abundant | Lacustrine |
| II | Oil and gas prone | Moderate | Marine |
| III | Gas prone | Small | Terrestrial |
| IV | Neither (primarily composed of vitrinite) or inert material | None | Terrestrial(?) |
See also
- Evaluating source rock quality
- Rock Eval analysis
- Visually assessing quality
- Pyrolysis gas chromatography
References
- ↑ Durand, B., 1980, Sedimentary organic matter and kerogen: definition and quantitative importance of kerogen, in Durand, B., ed., Kerogen: Techniq, p. 13–14.
- ↑ Tissot, B., P., Welte, D., H., 1984, Petroleum Formation and Occurrence, 2 ed.: New York, Springer-Verlag, 699 p. The best overall reference for petroleum geochemistry.
External links
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