Simulation Experiment of CO ₂ -Water-Rock Reaction Seepage Capacity in Gas Reservoirs with Different Lithology

CCUS-EGR is becoming the most cost-effective method for energy saving and emission reduction globally. However, the acidic nature of CO₂ can alter the reservoir permeability over time, affecting the stability and sustainability of gas injection. To explore this, long-term CO₂ injection simulations were conducted on tight sandstone, carbonate rock, and volcanic rock. By applying gas and water permeability calculation methods, the reservoir permeability was monitored in real time throughout the long-term displacement process. Combined with NMR measurements, cross-lithology comparison analysis was conducted to investigate the evolution characteristics of pore structure and flow capacity, as well as the key influencing factors in various lithological reservoir samples. The results show that the influence of long-term CO₂ replacement and shut-in well reinjection replacement on the seepage capacity of the rock samples mainly comes from the combined effects of clay expansion, mineral particle settling and plugging, and reaction dredging to increase infiltration, and the process of water-rock reaction involves mineral particles reacting, dissolving, dislodging, transporting, and plugging. The long-term replacement and shut-in well reinjection experimental process of dense sandstone seepage capacity slightly reduced or basically unchanged, due to the greater clay effect; with carbonate rock calcite and dolomite as the main components, CO₂-water-rock reaction is dominated by mineral dissolution and clearing channels to increase seepage, with a significant increase in seepage capacity; feldspar is abundant in volcanic rocks, leading to mineral precipitation and pore-blocking during CO₂-water-rock reaction. This results in mesopore enlargement and blockage of both micro- and macropores. The channel clearing and permeability enhancement are weaker compared with carbonate reservoirs, with only a slight increase in overall seepage capacity. These findings provide valuable guidance for the efficient implementation of the CCUS-EGR.