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Why do anaerobic microorganisms produce methane during the immature stage of hydrocarbon 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, methane is produced through the biological decomposition of organic material by specialized microorganisms known as methanogenic archaea.12

This process, often referred to as biogenic gas generation, occurs in environments that are strictly anaerobic, meaning they lack oxygen and are free from high concentrations of sulfate. The production of methane is a multi-stage metabolic process where various anaerobic bacteria first break down complex organic substrates into simpler compounds, such as carbon dioxide, hydrogen gas, or organic acids. Methanogens then utilize these end products to synthesize methane. By consuming hydrogen gas during this metabolic activity, methanogens also support the growth of other anaerobic bacteria in the mixture, creating a symbiotic environment that facilitates the continued breakdown of organic matter.123