Assessment and Prediction of Pore‐Scale Reactive Mixing From Experimental Conservative Transport Data

Abstract

We investigate the impact of pore-scale heterogeneity on reactive mixing using experimental data from inert fluid-fluid displacement in a quasi 2-D porous medium. We interpret the invading and defending fluids as the conservative components A+C and B+C of the instantaneous irreversible bimolecular chemical reaction A+B→C and determine the reaction product C. We find strong growth of the reaction rate at short and intermediate times due to deformation of the mixing interface and heterogeneity-induced increase of the mixing area. This behavior is captured by a dispersive lamella approach that quantifies the mixing dynamics at the interface in terms of temporally evolving effective dispersion coefficients. The latter capture the dominant controls on the evolution of the mixing interface, namely, advective heterogeneity and transverse mixing. Reactive transport formulations based on constant hydrodynamic dispersion coefficients are not able to describe the observed behavior due to the lack of complete mixing on the support scale, which is required for these approaches to hold. These results shed some new light on the origins of heterogeneity-induced mixing and reaction dynamics in porous media and their systematic upscaling. © 2020 American Geophysical Union.