The research on the mechanisms and applications of microorganisms and their metabolites in enhancing oil recovery in low-permeability reservoirs

Low-permeability reservoirs are characterized by low reservoir permeability and poor fluid mobility, resulting in long-term low recovery efficiency. This necessitates the development of efficient, cost-effective, and environmentally friendly enhanced oil recovery (EOR) technologies. This study focuses on microbial enhanced oil recovery (MEOR) technology, selecting Bacillus subtilis BS3096 and Pseudomonas aeruginosa LZ3-2 as model microorganisms to systematically evaluate the functions and mechanisms of their metabolites (lipopeptides and rhamnolipids) in improving oil recovery. Laboratory-simulated imbibition experiments were conducted to explore the critical roles of biosurfactants in reducing oil-water interfacial tension, altering rock wettability, and optimizing imbibition pathways, with comparisons to chemical surfactants. Results showed that lipopeptide biosurfactants significantly reduced the oil-water interfacial tension from 0.8848 mN/m to 0.2055 mN/m and decreased the contact angle from 116.4° to 42.8°, transforming rock wettability from oil-wet to water-wet and increasing oil recovery to 60%, outperforming chemical surfactants. Additionally, microbial cells achieved selective plugging of large pores in cores, directing imbibition fluids toward small pores in low-permeability zones, thereby further enhancing oil displacement efficiency. This study not only highlights the potential application value of microbial metabolites in improving oil recovery in low-permeability reservoirs but also provides scientific evidence and technical support for the industrial application of MEOR technology, offering practical insights for the development of efficient, cost-effective, and environmentally friendly EOR techniques.