Investigation of a hydrocarbon-degrading strain, Rhodococcus ruber Z25, for the potential of microbial enhanced oil recovery

A hydrocarbon-degrading strain, Rhodococcus ruber Z25, was isolated from the formation brine in Daqing Oilfield, China. The strain Z25 was able to grow under facultative anaerobic condition and produce biosurfactant while hydrocarbon was used as sole carbon source. The biosurfactant of R. ruber Z25 showed a perfect emulsification activity and was able to lower the interfacial tension to approximately 1.0 mN/m and achieved a CMC value of 57 mg/L. The biodegradation experiments of the crude oil by the strain Z25 under aerobic and anaerobic conditions exhibited positive effects in improving the physical properties of the crude oil, including mobility enhancement, cloud point reduction and wax degradation. Waterflooding experiments were done to investigate the MEOR potential of the strain and varied oil recovery efficiencies from 8.88% to 25.78% were achieved. The main MEOR mechanisms of the strain Z25 included hydrocarbon degradation, improvement of oil mobility, wettability alteration and selective plugging. These results revealed that strain Z25 exhibited a tremendous potential for MEOR application.