Microbial oil transformation processes accompanied by methane and hydrogen‐sulfide formation

Abstract

Abstract The pattern of distribution and the proportions of microorganisms belonging to several physiological groups present in the formation waters of water‐flooded petroleum‐bearing rocks of the Apsheron Peninsula were investigated. It was shown that hydrocarbon‐oxidizing bacteria occur predominantly in the near‐bottom zones of injection wells, accessible to dissolved oxygen. Anaerobic microorganisms (sulfate‐reducing, fermenting, and methanogenic bacteria) were present in all zones affected by water flooding. The variety of bacterial species present in oil‐bearing rocks was investigated. Using a radioisotope method, the existence of a contemporaneous process of methane generation in the formation waters of water‐flooded oil‐bearing rocks was revealed. Laboratory experiments showed that hydrogen, methane, and hydrogen sulfide generation from petroleum was possible in an aerobic‐anaerobic microbial succession. A sequence of processes of petroleum hydrocarbon modification, resulting in the accumulation of methane and hydrogen sulfide, was revealed. Aerobic oxidation of petroleum by hydrocarbon‐oxidizing bacteria resulted in the production of acetate and higher fatty acids. The products of the aerobic oxidation of petroleum were fermented with hydrogen and carbon dioxide release. Acetate, hydrogen, and carbon dioxide were direct substrates for meth‐anogenesis and sulfate reduction. In the latter process, higher fatty acids were also directly utilized. The possibility of syntrophic utilization of intermediate fatty acids and alcohols yielding methane and hydrogen sulfide is discussed.