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 CO 2 (scCO 2 ) 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 scCO 2, mineral dissolution and precipitation reactions, and the subsequent physical changes in the reservoir. The results indicate that the scCO 2 plume is predominantly confined within the reservoir, with minimal gas-phase CO 2 diffusion into the surrounding strata and a slight reduction in liquid-phase CO 2 concentration due to ongoing geochemical reactions with formation minerals after cessation of CO 2 injection. The injection process leads to the dissolution of calcite and magnesite, releasing ions such as Ca 2+, Mg 2+, and HCO 3 –, which promote the precipitation of dolomite and anhydrite. Near the injection well, the high CO 2 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 CO 2 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 CO 2 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 CO 2 sequestration, which are crucial for understanding pore-permeability evolution in depleted carbonate reservoirs.