Kerogen : Hydrocarbon
The primary source of hydrocarbons in the rocky underground is called kerogen: lumps of organic matter.
- Kerogen is the portion of naturally occurring organic matter that is non-extractable using organic solvents i.e. it is insoluble in solvents.
- It represents about 90% of the organic carbon in sediments.
- It occurs in source rock and may expel hydrocarbons upon thermal cracking.
- Typical organic constituents of kerogen are algae and woody plant material.
- It consists of lighter as well as heavier hydrocarbons and acts like a precursor of oil and natural gas.
- They have a high molecular weight relative to bitumen, or soluble organic matter. Bitumen forms from kerogen during petroleum generation.
- Kerogens are described as Type I, consisting of mainly algal and amorphous (but presumably algal) kerogen and highly likely to generate oil; Type II, mixed terrestrial and marine source material that can generate waxy oil; and Type III, woody terrestrial source material that typically generates gas.
- The types of kerogens present in a rock largely control the type of hydrocarbons generated in that rock.
- Different types of kerogens 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.
