Microbiome changes and characteristics under nutrient injection for enhanced oil production at Daqing oilfield

Current studies on Microbial Enhanced Oil Recovery (MEOR) mainly focus on introducing exogenous microbes or injecting biosurfactants into oil reservoirs, whereas simulating indigenous oil-displacing microorganisms has been less explored. In this study, we conducted MEOR applications on an oil reservoir in Daqing oilfield by injection of only nutrition solution (without microbial strains or biosurfactants), leading to an average increase of 218.6–221.4% in oil production. An alternative stable microbial community dominated by Pseudomonas species was established after MEOR applications, even one year after the termination of the injection. Additionally, members of Ca. Patescibacteria, Ca. Caldatribacteriota (JS1) and hydrogenotrophic methanogens Methanocorpusculum and Methanolinea were found as biomarkers for high oil productivity. These results demonstrate the potential to enhance crude oil production through biosurfactant production, acid and alcohol metabolites production, hydrocarbon degradation and biogas (CH₄ and N₂) production by the aforementioned stimulated indigenous oil-displacing microorganisms. This research provides theoretical guidance for the exploitation of depleted reservoirs and the extension of the development life of oil reservoirs.