Effects of Mixing at Pore Intersections on Large-Scale Dissolution Patterns and Solute Transport

The flow-induced dissolution of porous rocks governs many important subsurface processes and applications. Solute mixing, which determines pore-scale concentration fields, is a key process that affects dissolution. Despite its importance, the effects of pore-scale mixing on large-scale dissolution patterns have not been investigated. Here, we use a pore network model to elucidate the mixing effects on macroscopic dissolution patterns and solute transport. We consider two mixing rules at pore intersections that represent two end members in terms of the mixing intensity. We observe that the mixing effect on dissolution is the strongest at moderate Damköhler number, when the reactive and advective time scales are comparable. This is the regime where wormholes spontaneously appear. Incomplete mixing is shown to enhance flow focusing at the tips of the dissolution channels, which results in thinner wormholes and shorter breakthrough times. These effects on passive solute transport are evident independent of initial network heterogeneity.