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

Abstract

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.