What is Kerogen?
Kerogen is defined as the organic material in sedimentary rocks that is insoluble in organic solvents because of the huge molecular weight of its component compounds. The soluble portion is known as bitumen. Chemically, it consists of carbon, hydrogen, and oxygen with a minor amount of nitrogen & sulphur.
It is the process of most oil and gas, and this has three sources: marine, terrestrial, and recycled. The terrestrial kerogen has components similar to coal. It yields petroleum when it undergoes destructive distillation.
Types of Kerogen:
Based on the optical examination and physio-chemical analysis, three main types of Kerogen can be recognized,
Type-I (Algal or lipid-rich kerogen):
- These are essentially algal in origin
- It contains many aliphatic chains and feco aromatic model
- The H: C ratio is about 1.65
- This type has a higher proportion of hydrogen relative to oxygen (H: 0 is 1.2-1.7)
- The O/C ratio is <0.15
- Derived from algal lipids or from organic matter enriched in lipids by microbial activity. Lipids are dominant compounds with derivatives of oils, fats, and waxes.
- The potentiality of oil and gas generation is also high
- These Kerogen are characteristic of many oil shales, source rocks, and channel ores.
Type-II (Liptinite rich):
- Kerogen of intermediate composition
- This type is rich in aliphatic compounds with aromatics.
- The H: C ratio is greater than > 1 (1.28).
- The O: C ratio is 0.03 -0.18
- It is usually related to marine, organic, deposited in reducing environment with medium to high sulfur content.
- The original organic matter consisted of algal detritus but also contained material derived from zooplankton and phytoplankton.
Type-III (Humic):
- It contains a high percentage of polycyclic aromatic hydrocarbon and oxygenated functional groups plus some paraffinic coaxes.
- It has a much lower H/C ratio < 0-84.
- This is produced from the lignin of the higher woody plants (land)
- This humic material, if buried as peat, undergoes the diagenesis of coal
- This type of Kerogen tends to generate largely gas but little oil.
