Microscopic flow simulation of acid rock chemical reactions in multi-scale and multi-mineral porous media

Abstract

The process of mineral dissolution in acid-rock reactions is of research significance for various fields such as oil and gas development and carbon dioxide storage. Natural rocks often contain different types of mineral components, and sub-resolution nanoscale pores can affect flow, mass transfer, and reactions. This study aims to further investigate the effects of mineral component distribution and sub-resolution pores on dissolution under different acid injection conditions. By utilizing the Darcy-Brinkman-Stokes equations to couple multi-scale flow, we establish fluid mass conservation equations that consider the mass exchange between acid solutions and mineral components, as well as mass conservation equations for the mineral components. The results indicate that the presence of horizontally layered dolomite can lead to localized uniform dissolution under conditions of strong convective ability. Under high diffusion coefficients, the combination of dolomite with insoluble minerals is beneficial for breaking the stable dissolution front, and oscillations in curvature can enhance the breakthrough capacity of the acid. In the wormhole model, larger nanoscale pore sizes facilitate the breakthrough of the acid solution. However, under high diffusion coefficients, the differences in permeability growth and breakthrough capacity of the acid solution among different cores are significantly reduced. Quantitative comparisons further demonstrate that the distribution of minerals and pore sizes has a non-negligible impact on dissolution, with the differences in pore permeability growth for different mineral components and nanoscale pore distributions reaching up to 5.02 times and 10.2 times, respectively.