Acidizing dissolution and permeability enhancement mechanisms under mine water reinjection: CO₂-water Co-storage propose

This study investigates dissolution mechanisms and permeability enhancement in deep sandstone reservoirs during mine water reinjection, while exploring synergistic opportunities with CO₂-water co-storage technology. Through comprehensive laboratory experiments involving rock powder immersion and extended static acidization trials, we systematically evaluated acid neutralization capacity, mineral dissolution characteristics, and porosity-permeability evolution in target sandstone formations. Key findings demonstrate that the middle reservoir sections exhibit superior acid buffering capacity, with total dissolved solids (TDS) increasing by 2,197.04 mg/L in purified water systems - suggesting substantial permeability improvement potential. CT imaging combined with Kozeny-Carman modeling revealed porosity enhancements of 1.48 ~ 3.69 times and permeability increases of 4.77 ~ 70.24 times post-acidization, particularly in surface-connected pore networks. Numerical simulations predict hydraulic influence radius expansion of 1.8 ~ 4.2 times and cumulative water storage capacity escalation up to 60 times after sustained 700-day reinjection. As a novel contribution, we propose CO₂-water co-storage as an environmentally sustainable alternative to conventional acid reinjection. Experimental verification shows continuous CO₂ injection effectively acidifies mine water to pH 3.66, achieving hydrochloric acid-equivalent dissolution effects while eliminating corrosion risks and environmental hazards. This approach enables simultaneous reservoir permeability enhancement through in-situ mineral dissolution (calcite, dolomite, and feldspars) and dual carbon-water sequestration, reducing atmospheric CO₂ emissions. These insights advance sustainable reservoir management strategies that harmonize groundwater recharge efficiency with low-carbon objectives in mining regions, offering practical solutions for ecological preservation and resource utilization.