Study on the Synergistic Enhancement of Crude Oil Recovery by Bacillus Co-Culture Systems

Microbial-enhanced oil recovery (MEOR) is a promising technology for oilfield development. To improve MEOR efficiency, two functional strains—Bacillus mucilaginosus ZZ-8 and Bacillus amyloliquefaciens ZZ-11—were isolated and purified. The growth characteristics, biosurfactant production, and crude oil emulsification performance of these strains were systematically evaluated through single-strain cultures and a co-culture system (ZZ-8: ZZ-11 = 1:1). The results demonstrated that the co-culture system exhibited superior growth and functional performance compared to monocultures. The cell-free supernatant significantly reduced oil–water interfacial tension, decreasing the contact angle from 53.56 ± 1.3° to 28.78 ± 0.82°, thereby enhancing crude oil detachment from rock surfaces and improving oil displacement efficiency. Gas chromatography (GC) analysis further confirmed the co-culture system’s pronounced degradation of long-chain alkanes (C17–C35). In oil sand washing experiments, the 1:1 mixed-strain fermentation broth achieved a crude oil elution rate of 84.39%, representing an 89.80% increase over uninoculated medium. This study not only validates the synergistic effect of the B. mucilaginosus–B. amyloliquefaciens co-culture system in enhancing oil recovery but also provides a theoretical foundation and innovative strategy for its practical application in MEOR technology.