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Abstract: 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 1.0mN/m and achieved a CMC value of 57mg/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. [Copyright &y& Elsevier]

• A novel facultative anaerobic strain Chelatococcus daeguensis HB-4 was first isolated from Oilfield. • The strain HB-4 can degrade long chain hydrocarbons to shorter chains. • Core flooding tests demonstrated 20.5% oil recovery by microbial enhancement, and 59.8% viscosity reduction. • Strain HB-4 can be used for microbial enhanced oil recovery in heavy oil reservoirs. Biodegradation of crude heavy oil was investigated with Chelatococcus daeguensis HB-4 that was isolated from the produced fluid of Baolige Oilfield in China. Batch growth characterization and crude oil degradation tests confirmed HB-4 to be facultative anaerobic and able to degrade heavy oil. The oil degradation was found to occur through degrading long hydrocarbons chains to shorter ones, resulting in oil viscosity reduction. By mixing crude oil with glucose, or using sole crude oil as carbon source, the content of light fractions (C 8 -C 22) increased by 4.97% while heavy fractions (C 23 -C 37) decreased by 7.98%. It was also found that bioemulsifiers were produced rather than commonly observed biosurfactants in the fermentation process, which was attributed to the extracellular degradation of hydrocarbons. Core flooding tests demonstrated 20.5% oil recovery by microbial enhancement, and 59.8% viscosity reduction, showing potential of strain HB-4 for application in the oil industry, especially in enhanced heavy oil recovery. [ABSTRACT FROM AUTHOR]