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How does organic matter change into kerogen during the early stage of petroleum formation?

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Multiple large offshore petroleum oil rigs with cranes and equipment stand in the ocean, connected by walkways above the water. — petroleum Liquid petroleum (crude oil)—which is refined into gasoline, diesel, heating fuels, asphalt, plastics, and other useful chemical compounds—is often extracted from the ground using a series of drills and pumps.

During the immature stage of petroleum formation, organic matter—primarily the remains of single-celled planktonic plants and animals—is converted into kerogen through a process known as diagenesis.1

This transformation is driven by biological activity and chemical rearrangement. After the rapid burial of these remains within fine-grained sediments, anaerobic microorganisms (which thrive in the absence of oxygen) decompose the organic detritus. This bacterial alteration, combined with various physical and chemical changes, transforms the organic material into a dark-colored, insoluble substance called kerogen.12

While this stage is primarily focused on the creation of kerogen, it is also characterized by the generation of biogenic methane, which is the only hydrocarbon produced in commercial quantities during this early phase. This kerogen later serves as the essential precursor for the generation of crude oil and other hydrocarbons during the subsequent mature stage of thermal degradation.123