kerogen

Kerogen is a solid, insoluble organic matter found in sedimentary rocks, formed from the preserved remains of living organisms such as plankton and plants. It is the primary source material that, under burial and heat, generates petroleum and natural gas. Kerogen is typically abundant in fine-grained rocks like shales and siltstones and is often quantified by measures such as total organic carbon (TOC).

Kerogen is not a single compound but a mixture of macromolecules that have evolved through diagenesis and maturation. Its composition varies with the type of original organic matter and the depositional environment. Based on origin and hydrogen content, kerogen is commonly classified into four main types: Type I is hydrogen-rich and oil-prone (often from algal or lacustrine sources); Type II is also oil-prone but more mixed in origin (marine plankton); Type III is poorer in hydrogen and gas-prone (woody terrestrial material); Type IV is largely inert and non-generating.

Thermal maturation, driven by burial beneath successive sedimentary layers, alters kerogen toward the generation of hydrocarbons. As kerogen matures, its hydrocarbons are expelled from the source rock, first generating liquid oil within the oil window and later producing natural gas in the gas window. The specific temperature range depends on kerogen type and geological conditions. Geological exploration uses kerogen characteristics, along with measures like hydrogen index, atomic H/C ratio, and Rock-Eval pyrolysis data, to assess hydrocarbon generation potential.

In petroleum geology, kerogen serves as the primary source for hydrocarbons and a key indicator of a rock’s potential to generate oil and gas. It is also relevant to studies of past environments and carbon cycling.