Lattice Boltzmann simulation of dissolution-induced changes in permeability and porosity in 3D CO₂ reactive transport

Dissolution and precipitation of rock matrix are one of the most important processes of geological CO₂ sequestration in reservoirs. They change connections of pore channels and properties of matrix, such as bulk density, microporosity and hydraulic conductivity. This study builds on a recently developed multi-layer model to account for dynamic changes of microporous matrix that can accurately predict variations in hydraulic properties and reaction rates due to dynamic changes in matrix porosity and pore connectivity. We apply the model to simulate the dissolution and precipitation processes of rock matrix in heterogeneous porous media to quantify (1) the effect of the reaction rate on dissolution and matrix porosity, (2) the effect of microporous matrix diffusion on the overall effective diffusion and (3) the effect of heterogeneity on hydraulic conductivity. The results show the CO₂ storage influenced by factors including the matrix porosity change, reaction front movement, velocity and initial properties. We also simulated dissolution-induced permeability enhancement as well as effects of initial porosity heterogeneity. The matrix with very low permeability, which can be unresolved on X-ray CT, do contribute to flow patterns and dispersion. The concentration of reactant H⁺ increases along the main fracture paths where the flow velocity increases. The product Ca⁺⁺ shows the inversed distribution pattern against the H⁺ concentration. This demonstrates the capability of this model to investigate the complex CO₂ reactive transport in real 3D heterogeneous porous media.