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Abstract

Crude oil recovery technologies were unable to meet the growing energy demand in China. Microbial Enhanced Oil Recovery (MEOR) was one of the most effective recovery methods for the oil fields. Biosurfactant in oil degradation and emulsification changed the solid oil into liquid oil to be exploited. This was the most important mechanism of MEOR technology, but because of the complex geological conditions of different oil reservoir types, the microorganisms used in petroleum recovery lack enough environmental adaptability. Several high environmental adaptive capacity microfloras were screened, which withstand high temperature (30-80°C), salinity (NaCl concentration of 5-20%, w/v) and pH (5-9). Produced biosurfactant withstand 10-90°C, pH 5-12, NaCl concentration 1-20% (w/v). Further fermentation process optimization was carried out, and the active metabolites including bioemulsifiers, biosurfactants, acids and alcohol showed good potential for application. This can greatly improve the oil remaining after waterflood recovery from 11.55% to 30.78% by physical model. A variety of active microfloras which form a complex system can reduce the surface tension, improve emulsifying activity and emulsion stability. The surface tension (less than 30 mN/m) and emulsifying activity (more than 60%) were maintained at a strong level, better emulsification activity for crude oil can be maintained for more than 120 h, which showed potential industrial application. The composite microbial oil displacement agent with nutrients and trace elements has been injected into the oil well in Changqing Oilfield. Results showed that oil production of the low yielding well (0.2 T/day) was improved more than 3 times, the produced liquid water content decreased by more than 75%, from 85% reduced to 25%, oil recovery is improved by 5-8 times, from 0.15 T/d to 0.9 T/d.