What is Kerogen?

About Kerogen:

• It 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.