Objective CO₂ dissolution in water tends to induce mineral reactions, thus significantly changing the pore structure of rocks and further affecting their seepage and mechanical properties. This phenomenon poses a major impact on the suitability and long-term safety of geologic CO₂ sequestration engineering.

Methods Using a simulation technology that combines the lattice Boltzmann method (LBM) and the finite element method (FEM), this study systematically investigated the calcite dissolution characteristics of calcite-bearing rock samples under varying injection rates of a saturated solution of CO₂. Furthermore, the dynamic evolution patterns of the permeability and elastic parameters (bulk and shear moduli) of the rock samples were revealed.

Results and Conclusions At lower injection rates, the chemical reaction products became enriched in the mid-to-distal part of the samples, inhibiting calcite dissolution in this part. Consequently, the chemical reactions occurred merely near the injection port. As the injection rate increased, the saturated solution of CO₂ exhibited an enhanced capacity to penetrate samples and then diluted reactants. As a result, calcites in the mid-to-distal part could participate in the reactions, resulting in a more uniform spatial distribution of calcite dissolution positions across the samples. Calcite dissolution significantly enhanced the rock permeability, especially at higher injection rates. At lower injection rates (30‒150 m/a), the solute transport was primarily achieved by diffusion, leading to an insignificant increase in rock permeability. When the injection rate increased to 750‒18 750 m/a, the solute transport mechanism gradually transitioned into advection, leading to greater differences in the rock matrix structure and more pronounced permeability enhancement. For the fitting of the permeability-porosity relationship, the power function model generally exhibited fit index n ranging from 2.8 to 6.5, while the Carman-Kozeny model showed n values varying from 0.9 to 4.6. Notably, the n values of both models showed a monotonically increasing trend with an increase in the injection rate. Comparative analysis reveals that the Carman-Kozeny model outperformed the power function model in terms of prediction accuracy. Calcite dissolution significantly reduced the elastic properties of rocks. As the porosity increased from 0.44 to 0.56, both the shear and bulk moduli decreased by approximately 20%. Additionally, both moduli declined rapidly initially and then decreased slowly in the late stage. Such nonlinear evolution renders the power function model more advantageous than the traditional linear model. This study also revealed that the elastic properties of rocks experienced exacerbated degradation with an increase in the injection rate. Compared to the bulk modulus, the shear modulus was more sensitive to variations in the injection rate. This study determines the key mechanism where the fluid injection rate dominates the evolution of the permeability and mechanical properties of rocks by governing the spatial distribution of dissolution, providing a theoretical basis for assessing the long-term safety of geologic CO₂ sequestration sites.