Solid-to-liquid ratio regulates microbially mediated mineral transformation and reservoir pore-structure evolution under simulated geological CO2 storage conditions

Geological CO 2 storage is a critical strategy for carbon neutrality, and its long-term stability is strongly influenced by CO 2 -water-rock interactions in subsurface reservoirs. Microorganisms inhabiting deep geological formations can alter mineral dissolution and carbonate precipitation through their metabolic activities; however, the regulatory mechanisms of interfacial conditions, particularly the solid-to-liquid ratio, remain poorly constrained. In this study, Bacillus licheniformis was introduced into sandstone-CO 2 -brine systems under simulated reservoir conditions (50 °C, 10 MPa, and 40 g/L salinity) to investigate the effect of solid-to-liquid ratio on microbially mediated mineral transformation. Batch experiments with sandstone-to-brine mass ratios of 1:1, 1:5, and 1:10 were conducted with corresponding abiotic controls. Combining aqueous geochemistry, mineralogical analysis, microbial activity assessment, and multiscale pore characterization, we elucidated the coupled evolution of microbial responses, mineral reactions, and pore structures. The results reveal that solid-to-liquid ratio governs the competition between mineral dissolution and carbonate precipitation by regulating mineral availability, microbial activity, and ion transport. The 1:1 system favored mineral dissolution, resulting in enhanced release of Ca 2+ , Mg 2+ , and HCO 3 − and pore enlargement. The 1:5 system promoted microbial persistence and carbonic anhydrase activity, leading to the greatest pore-network contraction and permeability reduction from 47.056 to 40.861 mD. The 1:10 system exhibited the strongest carbonate enrichment, with CaCO 3 comprising 72.05 wt% of precipitates. These findings demonstrate that carbonate accumulation and pore restructuring evolve asynchronously and are governed by nonlinear interactions among microbial activity, mineral dissolution, and secondary mineral precipitation, providing new insights into microbial regulation of geological CO 2 storage.