Methanogenic biodegradation of petroleum in the Western Siberia basin and its significance for formation of giant gas pools

This presentation demonstrates geological and geochemical evidence suggesting that a significant portion of dry gases in giant gas pools in Western Siberia originated during methanogenic biodegradation of petroleum. Most important geological evidence include common association of dry gases with biodegraded oil legs or underlying biodegraded oil and condensate accumulations. Most important geochemical evidence include 13C-enriched CO2 in pools with biodegraded oil and distinctive hydrocarbon molecular and isotopic compositions of most gases in Cenomanian pools suggesting that they represent mixtures of biodegraded thermogenic gases and secondary microbial methane. This Western Siberia study and other recently recognized worldwide occurrences of methane from biodegraded petroleum suggest that secondary methanogenesis is a highly important pathway of natural gas generation.