Effect of heterogeneity on reactive convective dissolution

We investigate the impact of porous media heterogeneity on the dynamics of reactive convective density-driven dissolution. We study the convective dissolution of species A in a fluid containing a species B in presence of a binary reaction A + B → C. Fluid density is a function of the Rayleigh number of the species so that, depending on the nature of the species, convection can be enhanced or decreased (Loodts et al., 2014). It has been shown that in homogeneous systems chemical reaction can increase the dissolution fluxes. The impact of the porous media heterogeneity is, however, largely unknown.

To address the effect of heterogeneity on reactive convective dissolution we consider heterogeneous scenarios with horizontally stratified, vertically stratified, and log-normally distributed permeability fields. We analyze the resulting fingering pattern, mass of the reaction product, mixing length and reaction front topology. Results show that the reaction front progresses more rapidly in vertically stratified permeability fields than in horizontally stratified ones, where convective fingers spread laterally and struggle to move vertically. In horizontally stratified fields, the fingers appear thicker compared to those in vertically stratified fields. This observation is corroborated by the higher mixing lengths in the vertically stratified scenarios. The mass of the reaction product is also affected by the heterogeneity. Vertically stratified scenarios display the fastest growth of the reaction product while the horizontally stratified have the lowest reaction product. Homogeneous and log-normally distributed cases lay in between the two other scenarios. In log-normally distributed cases the reaction product, as well as the mixing length, are proportional to the anisotropy ratio between the correlation length in the vertical and horizontal directions.

References.

 V. Loodts, C. Thomas, L. Rongy, and A. De Wit. Control of convective dissolution by chemical reactions: General classification and application to CO₂ dissolution in reactive aqueous solutions. Physical Review Letters, 113:114501, 2014