Investigating Spatial Scaling Effects of Reactive Transport in Porous Media Using a Pore-Network Model

Abstract

Mineral reaction rates exhibit spatial scaling effects in porous media. Darcy-scale models often cannot adequately capture the effects of strong concentration gradients, heterogeneous distributions of reactive surface area and flow paths on mineral reaction rates. However, pore-scale models are computationally expensive, and the geometric information in the subsurface is hard to obtain. Therefore, we perform pore-network modeling which balances computational effort and modeling complexity. We implement a pore-scale reactive transport solver in FEniCS[1] to study how the concentration gradients of dissolved minerals affect overall reaction rates. In Figure 1, we observe the variation of the concentration gradient of the dissolving ion along the flow path, leading to a process dependence of the average dissolution rate, which is difficult to quantify at the Darcy scale. In contrast, pore-network models are capable of capturing the pore-scale heterogeneities in the concentration field. This work investigates how spatial heterogeneities of mineral concentration and reactive surface area affect overall reaction rates at the Darcy scale. We aim to provide a generalized upscaled rate law of mineral dissolution for the Darcy-scale model, which can be further implemented to the coupled reactive transport solver using DuMux[2] and Reaktoro[4][3].