Screening And Performance Evaluation Of Microbial Enhanced Oil Recovery Strains From Shale Oil Reservoir

China is rich in continental shale oil reserves,but it faces the problems of short production cycle（<10 years）and low oil recovery（3～10%）.Microbial enhanced oil recovery has the advantage of environment-friendly,and it is a promising technology to enhance oil recovery.Biosurfactant is a natural amphiphilic substance produced by microorganisms,which can reduce the interfacial tension of oil/rock and oil/water,disperse emulsified crude oil and change rock wettability,which is one of the potential means to enhance shale oil recovery.As the reservoir conditions are quite different and the types of biosurfactants suitable for different reservoirs are also different,the screening of strains suitable for specific reservoirs is the key to the efficient application of biosurfactants.Based on this,the purpose of this paper was to screen the biosurfactant-producing strains suitable for Jimusar shale reservoir and evaluate the flooding of the biosurfactants.Gram staining and 16s rDNA gene sequencing were used to observe the morphology and identify the two strains.The culture conditions of the strain were optimized by surface/interfacial tension test and emulsification test,and its stability under different pH,temperature and salt concentration was investigated.The physicochemical properties of biosurfactants produced by two strains were characterized by Fourier transform infrared transform（FTIR）and liquid chromatography-mass spectrometry（LC-MS）,and their flooding were evaluated by core flooding test.This study showed that the two strains Y1（Pseudomonas aeruginosa）and Y2（Bacillus subtilis）have good ability to produce biosurfactants,and their morphology is short rod.The surface activity of Y1 and Y2 was the best in the medium with glucose as carbon source and ammonium nitrate as nitrogen source,while the emulsifying activity was the best in the medium with lactose as carbon source and ammonium nitrate as nitrogen source.The biosurfactant produced by Y1 is a mixture of rhamnolipid of Rha-Rha-C₈,Rha-C₁₀-C₁₀ and Rha-Rha-C₁₀-C₁₀.The interfacial tension between the biosurfactant produced by Y1 and crude oil was more sensitive to the changes of pH and Na Cl concentration,and its stability was good in the temperature range of 40～80℃.The emulsifying capacity of Y1 supernatant was relatively stable under the conditions of pH value of 1～11 and temperature of 40～90℃.The analysis showed that the biosurfactant produced by Y2 was a lipopeptide mixture of C₁₅-Surfactin and C₁₆-Fengycin,and its surface activity was stable in the temperature range of 40～80℃and pH value of 1～11,but the interfacial tension value decreases with the increase of Na Cl concentration.The emulsifying ability of the biosurfactant produced by strain Y2 to crude oil showed a trend of first increasing and then decreasing with the increase of pH and temperature,and the emulsifying ability was the best when the temperature was 50～60℃.According to the core flooding results,the supernatants of strains Y1 and Y2 can enhance oil recovery about 9%and 6%,respectively,on the basis of water flooding.In summary,the two strains screened in this study had good surface activity and emulsifying activity,and can improve shale oil recovery to a certain extent by reducing oil/water interfacial tension and crude oil emulsification.This study can provide a potentially feasible technical route for the efficient development of microbial enhanced oil recovery in Jimusar shale oil.