Coupled Axial Deformation, Hydraulic and Geochemical Evolution of Basalt during CO₂-Saturated Brine Flow

Basalt is a promising geological medium for CO₂ storage because of its potential for permanent mineral trapping, although fluid–rock reactions can alter pore structure and hydraulic properties. This study investigates coupled axial deformation, hydraulic and geochemical evolution of basalt during CO₂-saturated brine flow at 88 °C and approximately 210 bar pore pressure. In situ axial deformation, differential pressure and apparent permeability were monitored continuously, while effluent chemistry, mineral saturation states and pore-structure properties were evaluated. Six axial deformation stages were identified, with a pronounced hydraulic transition after approximately 115 pore volumes (PV) injected. Larger deformation magnitudes coincided with decreasing differential pressure and increasing apparent permeability, and absolute axial strain change was positively correlated with stage-averaged apparent permeability (r = 0.919, R² = 0.8437). Absolute permeability increased from 2.41 to 8.55 mD, while measured porosity increased only slightly from 9.15% to 9.51%. Fe and SiO₂ concentrations generally increased during reactive flow, and late-stage saturation indices indicated thermodynamic favorability for selected secondary phases. Nitrogen adsorption measurements showed changes in accessible pore structure. These results demonstrate concurrent deformation, hydraulic and geochemical evolution and indicate that permeability evolution cannot be explained by changes in bulk porosity alone.