Results of the trial of the microbiological method for the enhancement of oil recovery at the carbonate collector of the Romashkinskoe oil field: Biogeochemical and productional characteristics

This paper presents results of a study of the effect of introduction of mol asses and Clostridium tyrobutyricum on the isotopic composition of carbon c ompounds and on oil recovery from bed 302 of the Romashkinskoe oil field. M olasses fermentation resulted in considerable variations in the isotopic co mposition of carbon compounds in the stratum. In the periods of the largest technological impact, isotopically light carbonates appeared in the stratu m that were formed from molasses, having a delta(13)C value of -27.9...-28. 5%. The delta(13)C/Sigma CO2 + HCO3- + CO32- value decreased from -12.2 to -20 and even -28.3%. The interaction of microbial metabolites (carbon dioxi de, volatile fatty acids) with the carbonate matrix (having a delta(13)C va lue of +0.4 to -4.0%) resulted in its dissolution and release of isotopical ly heavy carbonates, which correlated with an increase in calcium concentra tion in the stratal water. Consumption of isotopically light carbon dioxide by chemolithotrophic methanogens, whose activity increased considerably du ring the course of the experiment, led to the enrichment of the methane of the accompanying gas with the C-12 isotope and to a decrease in the delta(1 3)C/CH4 value from -42.3 to -54.8%. As a result of the biotechnological tre atment, oil recovery increased by 28.9% at the experimental site and the wa ter content in the extracted fluid decreased.