Metagenomic Analysis and Core Flooding Reveals the Indigenous Bacterial Community Information and MEOR Potential of the Main Water-Drive Low-Permeability Reservoir in the Ordos Basin.

Oil recovery decreased with prolonged waterflood development in the main reservoirs in the Ordos Basin, and the extraction of the remaining oil was gradually difficult. To exploit oil-producing potential through microbial enhanced oil recovery (MEOR), bacterial communities of 26 samples from Yan 9, 10 layers, and 15 samples from Chang 6 layers were analyzed based on high-throughput sequencing. 1578 and 3581 amplicon sequence variants were obtained from Jurassic and Triassic samples, and α diversity analysis showed that dominant bacterial genera existed distinctly in both study areas. The distribution of the Jurassic bacteria community differed from that of the Triassic, revealed by a principal coordinate analysis. (15.74%) and (9.94%) were identified as the dominant bacteria in the Jurassic study areas, as well as (33.54%) and (11.41%) were the main bacteria in the Triassic reservoirs. Co-occurrence network analysis indicated that the Jurassic and Triassic study areas had both complex and unstable bacterial consortiums, which were closely connected with and , respectively. The different development strategies and reservoir properties led to the discrepancy in indigenous bacteria distribution between the Jurassic and Triassic study areas. However, some bacteria that have been reported to have oil-displacing ability, such as , , , , and , were found in both regions, suggesting that these bacteria had extensive adaptability. Among them, the utilization of functional bacteria of and might be conducive to enhancing oil recovery stably. Based on this, Pseudomonas aeruginosa PA2 was isolated from study areas and enhanced oil recovery by 17.85 and 11.89% during Jurassic and Triassic core flooding tests, respectively.