In-situ lipopeptide biosurfactant production by Bacillus strains correlates with improved oil recovery in two oil wells approaching their economic limit of production

Significant amounts of entrapped oil could be potentially recovered from water-flooded reservoirs nearing their economic limit of production via biosurfactant-enhanced oil recovery. However, evidence for the persistence and metabolic activity of injected biosurfactant-producing bacterial species activity is lacking. We injected a glucose-nitrate-mineral nutrient mixture and two lipopeptide biosurfactant-producing Bacillus strains into two wells to correlate in-situ metabolism with oil recovery. Two wells producing from the same Viola formation were each inoculated with about 60 m3 of tank battery brine with a nutrient mixture containing glucose, sodium nitrate and trace metals and Bacillus licheniformis RS-1 and Bacillus subtilis subsp. subtilis spizizenii NRRL B-23049. Analysis of production water indicated in-situ growth of the injected strains and other heterotrophic fermenting bacteria, metabolism of the nutrients, and biosurfactant production. Both wells had a peak lipopeptide biosurfactant concentration of 20 and 28 mg/L, respectively, which is twice the minimum concentration required to mobilize entrapped oil from sandstone cores. Metabolic products of glucose fermentation in both wells were acetate, 2,3-butanediol, ethanol, formate, lactate, and succinate and cells and these products accounted for 107.6% of the glucose used. The increase in biosurfactant, acids, alcohols and carbon dioxide during the first 5 days after commencement of production corresponded directly with an increase in oil recovery. Wellhead measurements of total produced fluid, the water-to-oil ratio and the percentage of oil showed that about 52.5 m3 of additional oil (net cumulative increase) occurred during the first 60 days of sampling. These results showed the feasibility of stimulating in-situ biosurfactant production and its potential to improved oil production from mature oil reservoirs.

► Bioaugmentation of oil wells is feasible and leads to improved oil production.
► Lipopeptide biosurfactants were produced in an oil reservoir.
►  Metabolic products of Bacillus glucose fermentation were detected.
► Increase in biosurfactant and metabolic products correlated with oil recovery.
► Additional oil (net cumulative increase) was produced.