Kerogen

Depositional environment is the dominant factor in determining the types of organic matter found in a rock. Only two types of organic matter are found in rocks: land derived and aquatic algae derived. Heat and pressure convert organic matter into a substance called humin and then into kerogen. Time and temperature convert kerogen into petroleum.

What is kerogen?

Geochemists define kerogen as the fraction of sedimentary organic constituent of sedimentary rocks that is insoluble in the usual organic solvents. Kerogens are composed of a variety of organic materials, including algae, pollen, wood, vitrinite, and structureless material. The types of kerogens present in a rock largely control the type of hydrocarbons generated in that rock. Different types of kerogen 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.

Structured kerogens include woody, herbaceous, vitrinite, and inertinite. Amorphous kerogens are by far the most prevalent and include most of the algal material.

Kerogen quality

The type of kerogen present determines source rock quality. The more oil prone a kerogen, the higher its quality. Four basic types of kerogen are found in sedimentary rocks. A single type or a mixture of types may be present in a source rock. The table below lists and defines these four basic kerogen types.

Kerogen type	Predominant hydrocarbon potential	Amount of hydrogen	Typical depositional environment
I	Oil prone	Abundant	Lacustrine
II	Oil and gas prone	Moderate	Marine
III	Gas prone	Small	Terrestrial
IV	Neither (primarily composed of vitrinite) or inert material	None	Terrestrial(?)

See also

• Evaluating source rock quality
• Rock Eval analysis
• Visually assessing quality
• Pyrolysis gas chromatography

External links

find literature about Kerogen

• Original content in Datapages
• Find the book in the AAPG Store