Effects of pore-scale fluid flow on fluid-solid reactions in porous and fractured media

Abstract

Fluid-solid reactions, such as mineral dissolution and precipitation, are fundamental processes that govern various subsurface processes and engineering applications that are critical to addressing global water, climate, and energy issues. Recent studies have shown that fluid flow is one of the key controlling factors in fluid-solid reactions because it significantly affects the concentration gradients of reactants at the fluid-solid interfaces. Subsurface flow rates exhibit significant variability, and fluid inertia can play an important role. In porous and fractured media, inertial flows readily induce complex flow structures, such as recirculating flows. Such pore-scale flow structures can significantly alter fluid-solid reactions by controlling the pore-scale concentration fields. In addition, recent studies have shown that the recirculating flow topology differs between two-dimensional (2D) and three-dimensional (3D) systems, potentially leading to fundamental differences in reactive transport dynamics. However, most previous studies have investigated fluid-solid reactions in 2D systems without considering fluid inertia, and our understanding of the role of fluid inertia and 3D flow in fluid-solid reactions remains elusive. To address this knowledge gap, we study mineral dissolution and precipitation processes over a wide range of flow conditions in both 2D and 3D systems using numerical simulations and laboratory experiments. Our results show that pore-scale fluid inertia and 3D flow fundamentally alter the dynamics of mineral dissolution and precipitation and their upscaled behavior, compared to non-inertial and 2D systems. Our findings provide significant insights for improving our understanding of fluid-solid reactions and the predictability of field-scale models.