Inertia Effects on Effective Reaction Rates with Fluid-Solid Reactions in 3D Porous Media

Flow velocity can vary over wide ranges in subsurface systems, and fluid inertia is an important factor that controls biogeochemical reactions. Fluid inertia in heterogeneous porous media often induces complex flow structures, such as preferential and recirculating flows. The complex flow structures in turn control concentration gradients of reactants near solid surfaces, thereby affecting effective reaction rates. For example, recirculating flows are shown to cause transport-limited reaction conditions by controlling reactant concentration distribution, thereby affecting effective reaction rates in 2D porous media [Deng et al., 2018, Geochim Cosmochim Acta]. However, we do not have a comprehensive understanding of the inertia effects on effective reaction rates in 3D porous media. It is important to understand the inertia effects in 3D systems because 3D flow topology can be fundamentally different from 2D flow fields, but most studies on the inertia effects on reactive transport are limited to 2D systems. In this study, our aim is to improve our fundamental understanding of the fluid inertia effects on effective reaction rates in heterogeneous 3D porous media. We run 3D pore-scale reactive transport simulations with a fluid-solid reaction in 3D porous media generated based on real rock CT images. We obtain steady-state flow fields using an open-source CFD code, OpenFOAM, and run an in-house reactive transport code that solves the advection-diffusion-reaction equation with an irreversible first-order reaction at fluid-solid interfaces. We then estimate effective surface reaction rates at various combinations of Reynolds (Re) and Peclet (Pe) numbers by changing flow rates and diffusion coefficients. By independently changing Reynolds and Peclet numbers, we compare the inertia and diffusion effects on effective reaction rates and elucidate the importance of the inertia effects on effective reaction rates in 3D porous media. This work provides a foundation for upscaling the inertia effects on reactive transport with fluid-solid reactions. Acknowledgement: This research was supported by the Korea Environmental Industry and Technology Institute (KEITI) (Project Number: 2018002440003).