Abstract: In view of the poor adaptability of microbial activated water flooding to Sai169 low-permeability reservoir, Changqing Oilfield, the types and contents of metabolites such as biosurfactants, organic acids and biogas in microbially activated water in the on-field expanding culture insert were quantified by gas chromatography-mass spectrometry and other testing methods, the mechanism of micro oil displacement was clarified, and the microbial community distribution in the produced fluid of 22 wells was sequenced by the paired-end sequencing method. The results of the study showed that the mass concentration of esters in the microbial metabolites ranged from 1.57 to 4.98 mg/L, the mass concentration of organic acids ranged from 108.34 to 133.61 mg/L, the volume concentration of biogas ranged from 18 to 38 mL/L, the oil-water interfacial tension was reduced by 30% to 70%, the pH value was reduced by 3% to 5%, and the oil displacement efficiency was increased by 5.46 to 11.93 percentage points; the biosurfactants, organic acids, biogas and biopolymers in the microbially activated water metabolites played an important role in oil displacement; the gene numbers of bacteria, archaea and methanogens in the fluids of production wells generally increased in the process of microbial flooding, and the differences in distribution between wells gradually decreased; the differences in microbial communities between wells were mainly related to permeability and injection-production horizons. This study provides an important theoretical basis for microbial flooding, formation and well selection, and optimization of injection-production scheme in low-permeability heterogeneous reservoir.

Key words: microbial flooding, low-permeability reservoirs, activated water flooding, oil displacement mechanism, microbial community, metabolites