Occurrence and geochemical activity of microorganisms in high-temperature, water-flooded oil fields of Kazakhstan and Western Siberia

The distribution of different methanogenic and sulfate-reducing bacteria and their activity in formation waters of Uzen, Mykhpay, and Talinskae oil fields, characterized by temperatures of the strata of 50-70 degrees C and higher, were investigated. Injection of surface waters was shown to result in development of biogenic oil transformation The temperature of injected waters determined the temperature regime and the presence of either mesophilic or thermophilic microorganisms in the microbial community near the bottom zone of injection wells. The number and activity of thermophilic microorganisms in the zone of producing wells were low or absent. Despite the absence of oxygen in the injected water, active microbiological processes occurred in the water-flooded oil fields. We concluded that the development of biogenic processes in oil fields proceeded not only as an aerobic-anaerobic microbiological succession but also as anaerobic transformation of organic matter injected with the surface water and of components of the oil itself.