Microcontinuum approach to multiscale modeling of multiphase reactive flow during mineral dissolution

Image-based modeling of mineral dissolution poses challenges due to its multiscale nature, requiring the consideration of multiphase reactive flow and transport at both the resolved pore scale (macropores/fractures) and the unresolved Darcy scale (micropores). The existing hybrid-scale simulation methods pose difficulties in handling the multiscale fluid-rock interactions and temporal structural evolution. In this study, we propose a multiscale compressive continuum species transfer (MC-CST) scheme to address the limitations of the standard CST scheme, which exhibits numerical diffusion issues at the gas-liquid interface and thereby suffers from inaccuracies in reactive transport simulations. The proposed scheme incorporates an additional compressive term derived from volume-averaging principles for the advection and diffusion fluxes in a single-field framework. To ensure the impermeable species transport condition at the solid boundary, a concentration extrapolation algorithm is developed. Four validation cases are conducted to demonstrate the model's capability in accurately simulating multiphase reactive flow and transport at various scales, including pore scale, continuum scale, and hybrid scales. Special attention is given to accurately modeling the thermodynamic conditions at the gas-liquid interface, particularly with respect to the concentration jump under conditions of large local Péclet numbers. Furthermore, we present a case study simulating calcite dissolution in a porous medium to underscore the importance of multiscale fluid-rock interactions for an in-depth comprehension of the dissolution regime.