Effect of reaction rate and pore structure heterogeneity on reactive solute transport in porous media

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CO2 geological storage is the most direct and reliable method to reduce CO2 emission, and deep saline aquifers have the greatest storage potential of CO2. In the process of CO2 storage in saline aquifers, mineral precipitation and dissolution caused by reactive solute transport have a significant impact on reservoir storage potential. In order to predict the transport characteristics and storage potential of CO2 in saline aquifers, it is critical to understand the relationship between chemical reactions and transport properties. The governing equations of porosity evolution of porous media considering chemical reaction processes are proposed, and the relationship between effective reaction area and porosity is considered, and finally a kinetic model is established. Considering different reaction rates and different pore structure heterogeneity, the evolution characteristics of porosity, species concentration and fluid pressure were obtained by combining advection-diffusion equation and Darcy's law. The simulation results show that the dimensionless porosity of porous media transforms from uniform variation to extreme non-uniform variation under low Da number, typical Da number and high Da number condition. The dimensionless concentration can not reach the saturation concentration under low Da number condition. The dimensionless concentration decreases significantly in the inlet region and reaches the saturation concentration under typical Da number condition. The dimensionless concentration reaches the saturation concentration rapidly in the inlet region under high Da number condition. The variation of dimensionless pressure gradient in porous media is significantly correlated with the porosity distribution. The dimensionless advection mass flux of porous media is negatively correlated with the pore structure heterogeneity, while the dimensionless diffusion mass flux is positively correlated with the pore structure heterogeneity. The specie peak concentration decreased with increasing heterogeneity, and the time to reach the peak concentration increased with increasing heterogeneity. The research results can provide a theoretical foundation for the assessment of the transport pathways of CO2 storage in saline aquifers.