Anomalous Transport in Dissolving Porous Media: Transitions Between Fickian and Non-Fickian Regimes

Abstract

Mineral dissolution is a key geologic process with broad impacts on natural processes and human activities. Depending on the interplay between advection, diffusion, and reaction rates, mineral dissolution can produce various dissolution patterns, such as wormholing and uniform dissolution. The resulting changes in pore structure directly influence the flow field, which in turn control solute transport behavior. In this study, we conducted numerical modeling of mineral dissolution and solute transport in pore networks to investigate how initial network heterogeneity and dissolution regimes affect transport dynamics. Our findings show that wormholing increases network heterogeneity by creating preferential flow paths and stagnation zones, resulting in a transition from Fickian to non-Fickian transport. Conversely, uniform dissolution extensively homogenizes the pore network and the flow field, leading to a transition from non-Fickian to Fickian transport, even in networks with high initial heterogeneity. Based on the initial heterogeneity and Damköhler number, transitions can be predicted.