Kerogen
|
|
Kerogens are chemical compounds, often found to be formed by the low-grade metamorphism (i.e. diagenesis) of organic molecules derived from decaying plant and animal matter. These are long-chain polymers which do not dissolve in several specific solvents.
Kerogens are the precursors to hydrocarbons (fossil fuels), and are also the material that forms oil shales.
| Contents |
Types
Labile kerogen breaks down to form heavy hydrocarbons (i.e. oils), refractory kerogen breaks down to form light hydrocarbons (i.e. gases) and inert kerogen forms graphite.
A Van Krevelen diagram is one example of classifying kerogens, where they tend to form groups when the ratios of hydrogen to carbon and oxygen to carbon are compared.
Type I
- Hydrogen:Carbon ratio > 1.25
- Oxygen:Carbon ratio < 0.15
- Tend to produce oil.
Type II
- Hydrogen:Carbon ratio < 1.25
- Oxygen:Carbon ratio 0.03 to 0.18
- Tend to produce a mix of gas and oil.
Type II-Sulfur
- Similar to Type II but high in sulfur.
Type III
- Hydrogen:Carbon ratio < 1
- Oxygen:Carbon ratio 0.03 to 0.3
- Material is thick, resembling wood or coal.
- Tend to produce gas.
Type IV (residue)
- Hydrogen:Carbon < 0.5
Origin material
The type of material is difficult to determine but several apparent patterns have been noticed.
- Ocean or lake material often meet kerogen type III or IV classifications.
- Ocean or lake material deposited under anoxic conditions often form kerogens of type I or II.
- Most higher land plants produce kerogens of type III or IV.
- Some coal contains type II kerogen.
Extraterrestrial material
- Carbonaceous chondrite meteorites contain kerogen-like components. Such material is believed to have formed the terrestrial planets.
- Kerogen materials have been detected in interstellar clouds and dust around stars.
See also: petroleum geology.