Reactive Transport in Evolving Porous Media

Abstract

Reactive transport modeling is a process-based approach that accounts for advection, diffusion, dispersion and a multitude of biogeochemical reactions. The occurrence of these reactions, by nature, tends to affect the properties of porous media in many ways (Tenthorey and Gerald 2006). If these alteration reactions are significant, then feedback mechanisms could occur that influence the flow of groundwater as well as the migration of solutes and gases through porous media (Le Gallo et al. 1998; Kaszuba et al. 2005; Jin et al. 2013). In addition, changes induced by the reactions on the solid grains can also affect the rates of the reactions themselves (Hao et al. 2012; Harrison et al. 2017). A prime example for reactive transport in evolving porous media is the dissolution of mineral phases. If dissolution reactions are substantial, the porosity, i.e., the void space between grains or apertures of fractures in jointed rocks, will increase. Such an increase in porosity commonly has secondary effects, by altering the connectivity or larger scale pores in the porous medium under consideration (Navarre-Sitchler et al. 2009). Together, these changes in porosity and connectivity can substantially affect flow and transport processes by modifying the key transport parameters such as the medium’s permeability and tortuosity, leading to alteration of the groundwater flow regime and modification of transport pathways. The impact of these changes can affect transport in the water phase as well as in the gas phase. In addition, because mineral dissolution reshapes the surface of the dissolving phases or leads to the complete dissolution of smaller particles, the system’s reactivity can be affected as well, leading to a direct feedback on reaction progress and rates (Noiriel et al. 2009).