Biosurfactant production under diverse conditions by two kinds of biosurfactant-producing bacteria for microbial enhanced oil recovery

Abstract

Stable growth and efficient production of biosurfactant by functional bacteria in oil reservoirs are indispensable for MEOR process. Biosurfactant production of bacteria has been mainly studied under aerobic conditions, but information on biosurfactant production under diverse conditions is still scarce. Two kinds of common biosurfactant-producing bacteria (Bacillus amyloliquefaciens 702 and Pseudomonas aeruginosa 709) were isolated from production fluid of Xinjiang oil field, China. Biosurfactant production by two strains was investigated under aerobic conditions, anaerobic conditions and high pressure (10 MPa) conditions, respectively. Under aerobic conditions, both B. amyloliquefaciens 702 and P. aeruginosa 709 decreased the surface tension of aerobic culture to lower than 27 mN/m at temperatures (25°C-40 °C), pH values (6.0–9.0) and less than 30 g/l NaCl. Strains 702 and 709 can aerobically produce 1582.4 mg/l and 8237.5 mg/l of biosurfactant. Both two aerobic cultures emulsified crude oil with EI24 values up to 84%. Both biosurfactant produced by strains 702 and 709 are thermo-stable and halo-tolerant. Although both two strains can grow under anaerobic conditions or high pressure conditions, only strain 709 efficiently produced biosurfactant under these conditions. Results of core flooding tests showed that another 7.04% of original crude oil was displaced through in situ production of biosurfactant by strain 709, and 1.10% of original crude oil was recovered by strain 702. Strain P. aeruginosa 709 can efficiently produce biosurfactant under anaerobic and high pressure conditions, so it is more suitable and advantageous for in situ MEOR applications. The feasibility of in situ production of biosurfactant used in oil fields was also discussed.