CO₂ Sequestration: Influence on Mineral Dynamics and Reservoir Permeability in Depleted Carbonates

To investigate the evolution of pore-permeability induced by mineral dissolution and precipitation during supercritical CO2 (scCO2) sequestration in matrix-fracture discontinuous depleted carbonate reservoirs, a 3D geological model incorporating THMC processes was developed based on Luojiazhai reservoir characteristics. This study thoroughly examines the migration behavior of scCO2, mineral dissolution and precipitation reactions, and the subsequent physical changes in the reservoir. The results indicate that the scCO2 plume is predominantly confined within the reservoir, with minimal gas-phase CO2 diffusion into the surrounding strata and a slight reduction in liquid-phase CO2 concentration due to ongoing geochemical reactions with formation minerals after cessation of CO2 injection. The injection process leads to the dissolution of calcite and magnesite, releasing ions such as Ca2+, Mg2+, and HCO3–, which promote the precipitation of dolomite and anhydrite. Near the injection well, the high CO2 concentration inhibits geochemical reactions, resulting in limited mineral dissolution and precipitation. In contrast, more substantial chemical reactions occur approximately 200 m from the injection well, where CO2 concentrations are lower. The interplay between mineral dissolution and precipitation significantly affects the reservoir’s porosity and permeability, with an initial increase during the first five years of CO2 injection followed by a continuous decrease due to subsequent mineral precipitation. The most notable changes in porosity and permeability are observed 200 m from the injection well, where geochemical reactions are most intense. These findings offer valuable insights into the mechanisms of mineral dissolution and precipitation induced by CO2 sequestration, which are crucial for understanding pore-permeability evolution in depleted carbonate reservoirs.