Biostimulation Sustains a Carbonic Anhydrase‐Producing Bacterial Consortium for CO 2 Hydration and Residual Oil Utilization Under Simulated Reservoir Conditions

Depleted oil reservoirs are potential targets for geological CO 2 storage; however, temperature, salinity, pressure, and nutrient scarcity can suppress microbial activity. In this study, a consortium comprising the carbonic‐anhydrase‐producing bacterium Bacillus licheniformis S5 and the petroleum‐degrading bacterium Bacillus cereus S0 was evaluated in a stirred high‐pressure liquid system containing simulated brine and residual crude oil. Nitrogen and phosphorus biostimulation promoted culturable growth. At 50°C and 10 MPa, the S5 + S0 consortium maintained higher colony‐forming unit (CFU) counts and more persistent apparent carbonic‐anhydrase‐associated esterase activity than either monoculture. S0‐mediated crude‐oil degradation produced fatty‐acid intermediates and surface‐active metabolites, reducing surface tension to 62.14 mN/m and increasing aqueous CO 2 mass transfer. Meanwhile, S5‐associated carbonic anhydrase activity promoted CO 2 hydration, and the consortium maintained HCO 3 − concentrations above 900 mg/L. Collectively, these findings support a bench‐scale mechanistic framework in which residual‐oil utilization, interfacial modification, and enzymatically mediated CO 2 hydration are functionally coupled under simulated reservoir‐fluid conditions. This framework provides a foundation for subsequent evaluation in oil‐bearing rock microcosms and core‐flood systems.