CHARACTERISTICS OF MICROBIOLOGICAL PROCESSES IN A WATER-FLOODED OIL-FIELD IN THE MIDDLE OB REGION

It was shown that in flooded high-temperature strata of the Mykhpai oilfield, which is characterized by low mineralization of the stratal water, hydrocarbon-oxidizing, sulfate-reducing, and methane-reducing microorganisms are widely distributed. In samples of water extracted from injection and producing wells, numbers of mesophilic and thermophilic methane-forming bacteria amounted to 10-10,000 cells/ml. Microorganisms forming methane on a medium containing acetate and methanol occurred in larger quantities than organisms developing on a medium containing H-2 and CO2. The rate of thermophilic methanogenesis (60-degrees-C), measured by the radioisotope method, was 0.74-5.44-mu-l CH4/liter per 24 h. A characteristic of the process is the unusually large contribution of acetate in methane formation, reaching 90%. The delta-C-13 value for methane extracted from the stratal liquids varied in the range -46.2 to -62.3%. The reasons for the relative heaviness of methane extracted from the critical zones of injection wells are discussed.