Microbiological investigation of the stratal waters of the Romashkinskoe oil field in the course of a trial of a biotechnology for the enhancement ofoil recovery

This paper presents results of a complex study of the ecosystem of an oil s tratum subjected to strong technological impact. Introduction of a large am ount of molasses containing 40% sucrose and of the fermentative bacteria Cl ostridium tyrobutyricum (earlier isolated from the same stratum) resulted i n significant changes in the microbiological and physicochemical characteri stics of the ecosystem. The cell number and activity of fermentative bacter ia and methanogens increased in the stratal water; the cell number and acti vity of sulfate reducers exhibited complex dynamics. The activity of fermen tative bacteria led to a decrease in the pH value of stratal water, the acc umulation of molasses fermentation products (lower alcohols and volatile fa tty acids), and an increase in the concentration of dissolved carbonates an d calcium. In the composition of gas, the content of CH4 and CO2 increased; in some zones of the stratum, an increase in H2S content occurred. In some samples, the density and dynamic viscosity of oil decreased.