Dynamics of Microbial Processes in the Stratal Waters of the Romashkinskoe Oil Field

The dynamics of the microbial processes developing in parallel with the exploitation of the Romashkinskoe oil field (Tatarstan) were studied in two areas differing in the degree of stratal water freshening. Flooding of the strata, in conjunction with purposeful measures on stratal microflora activation, was shown to increase the microbial population density and activate both methanogenesis and sulfate reduction; the latter process was limited by the low sulfate concentration. Development of anaerobic processes correlated with changes in acetate concentration in the stratal water. High mineralization (over 200 g/l) inhibited the stratal water microflora even if other conditions were favorable. Isotopic analysis of the carbonate carbon showed that the bicarbonate concentration increased in the stratal water due to microbial degradation of oil hydrocarbons and further participation of the biogenic carbon dioxide in dissolution of the carbonate cement of the oil-bearing strata. In strongly desalinated stratal water, the proportion of the newly formed bicarbonate was as high as 80%.