Kerogen
Kerogen is a waxy, insoluble organic substance that forms when organic rich shale is buried under several layers of sediment and is heated. If this kerogen is continually heated, it leads to the slow release of fossil fuels such as oil and natural gas, and also the non-fuel carbon compound graphite.[2] Shales that are especially rich in kerogen can actually be burned directly, but have seen limited use as a fuel throughout history.[3] During petroleum generation, bitumen also forms from kerogen.[4]
Kerogen is considered to be a major carbon sink in the carbon cycle, containing nearly 1016 tonnes of carbon.[5] The ability to study kerogen has also led to insight in the formation of sedimentary rocks and how organic materials are incorporated into these rocks.
The table below lists the four different types or classes of kerogen.
| Type | Characteristics[4] |
|---|---|
| I | Consists mainly of algae and is the most likely type of kerogen to produce oil when exposed to high temperatures. |
| II | Composed of a mix of terrestrial and marine organic materials and can sometimes produce oil. |
| III | Composed mainly of wood-like material along with some algae and plankton, generally creating natural gas, and some oil |
| IV | Type IV kerogen does not produce oil or natural gas. |
Formation
The formation of kerogen represents a major step in the formation of oil and natural gas, as kerogen serves as the source of fossil fuels. For kerogen to form, dead phytoplankton, zooplankton, algae, and bacteria must sink to the bottom of an ancient still water environment. After, this dead material must mix with inorganic, clay-like materials that enter these oceans from streams and rivers. This creates an organic-rich mud: which cannot be exposed to too much oxygen, otherwise the organic matter within the mud will be decomposed too quickly by bacteria. Before the organic matter is destroyed, it is buried by more sediment and lithifies (becomes sedimentary rock), creating organic shale.[2] If this shale is buried between 2 and 4 kilometers in depth, its temperature increases due to its location in the Earths interior. The increased temperature and pressure of the shale finally transforms it into kerogen.[3]
For Further Reading
- Geologic time scale
- Oil formation
- Natural gas formation
- Coal formation
- Stratigraphy
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References
- ↑ Wikimedia Commons. (May 14, 2015). Oil Shale [Online]. Available: http://commons.wikimedia.org/wiki/File:OIL_SHALE._IT_IS_THE_KEROGEN_IN_THIS_ROCK_WHICH_WHEN_HEATED_TO_900_F.,_YIELDS_OIL_-_NARA_-_552547.jpg#/media/File:OIL_SHALE._IT_IS_THE_KEROGEN_IN_THIS_ROCK_WHICH_WHEN_HEATED_TO_900_F.,_YIELDS_OIL_-_NARA_-_552547.jpg
- ↑ 2.0 2.1 Stephen Marshak. (May 14, 2015). Earth: Portrait of a Planet, 3rd ed. New York, NY, U.S.A:W.W. Norton & Company, 2008
- ↑ 3.0 3.1 Richard Wolfson. Energy, Environment and Climate, 2nd ed. New York, U.S.A.: Norton, 2012, pp. 96-97
- ↑ 4.0 4.1 Oilfield Glossary. (May 14, 2015). Kerogen [Online]. Available: http://www.glossary.oilfield.slb.com/en/Terms.aspx?LookIn=term%20name&filter=kerogen
- ↑ C. Largeaub,M. Vandenbrouckea. (May 14, 2015). "Kerogen origin, evolution and structure", ScienceDirect, vol.38 no.5, pp.719-833, 2007.
