Abstract:[Objective] To screen the indigenous functional microorganisms in reservoirs and explore their oil recovery mechanisms, we conducted field tests to determine the process and technical feasibility of enhancing crude oil recovery by indigenous microorganisms. [Methods] Wecollected samples from the Yingdong Oilfield and used oil plates to screen for the target bacteria. Next, we evaluated the environmental adaptability and optimized the culture conditions of the strain. Further, we measured the emulsifying, viscosity-reducing, paraffin-resistant, and hydrocarbon conversion abilities of the isolate to evaluate the oil recovery competence of the strain and explored its oil recovery mechanism. Finally, we carried out the microbial enhanced oil recovery tests in the oilfields. [Results] We isolated Bacillus velezensis B6 from the oil-water sample with an emulsifying activity index (EI24) of 100.00%, a viscosity reduction rate of 97.20%, and a paraffin resistance rate of 86.90%, which indicated that strain B6 had good emulsifying and viscosity-reducing abilities and improved oil recovery potential. Strain B6 could reduce heavy components in crude oil and increase light hydrocarbons to improve crude oil properties and quality. Moreover, we carried out single-well huff and puff and paraffin removal operations in Yingdong Oilfield, Yuejin Oilfield, and Huatugou Oilfield with a total of 62 well-times in the field test, which resulted in a cumulative oil increase of 1 460.36 tons and an average delay of 47 days in the well flushing cycle. The economic benefit was CNY 3.425 million, and the input-output ratio was 1:4. [Conclusion] The laboratory studies and field tests proved that indigenous B. velezensis B6 can significantly improve the oil recovery and well paraffin removal, with great application potential.
