Enhanced steady-state dissolution flux in reactive convective dissolution

Abstract

Chemical reactions can accelerate, slow down or even be at the very origin of the development of dissolution-driven convection in partially miscible stratifications when they impact the density profile in the host fluid phase. We numerically analyze the dynamics of this reactive convective dissolution in the fully developed non-linear regime for a phase A dissolving into a host layer containing a dissolved reactant B. We show for a general A + B → C reaction in solution, that the dynamics vary with the Rayleigh numbers of the chemical species, i.e. with the nature of the chemicals in the host phase. Depending on whether the reaction slows down, accelerates or is at the origin of the development of convection, the spatial distributions of species A, B or C, the dissolution flux and the reaction rate are different. We show that chemical reactions can enhance the steady-state flux as they consume A and can induce more intense convection than in the non-reactive case. This result is important in the context of CO geological sequestration where quantifying the storage rate of CO dissolving into the host oil or aqueous phase is crucial to assess the efficiency and the safety of the project.

Chemically-driven convective dissolution

“…When the product C is less dense than the reactant B (DR CB o 0), there exists a local minimum in the density profile due to the formation of C at the reaction front and the density profile is non-monotonic. Although the stabilizing non-monotonic profiles were studied previously, 18 we further differentiate here regimes IA and IB based on the amplitude of the end point values (r I , r b ). In regime IA, the density at the interface r I is smaller than or equal to the initial density of the host solution r b (r I r r b ) while in regime IB, the density at the interface is larger than or equal to the initial density of the host solution (r I 4 r b ).…”

“…Species A is consumed by the reaction to produce the denser C. The fingering pattern has been shown to be mainly due to the sinking of dense C towards the bottom and by continuity, the displacement of B from the bottom towards the reaction front. 18 This implies the presence of more reactant B close to the interface to react with A which increases the dissolution flux of A. The rapid merging and birth of fingers enhances the mixing between the two phases and leads to strong convective mixing in the host phase.…”

“…It was previously shown that reactions can accelerate or decelerate the convective dynamics with respect to the nonreactive case 14,16 and that the asymptotic dissolution flux of species A increases linearly with DR CB with a change of slope at DR CB = 0. 18 More precisely, when the product C is denser than the reactant B (DR CB 4 0), the density profiles are monotonic with an increased density at the interface. If C is sufficiently denser (i.e.…”

“…Recently, chemical reactions have been shown to be able to affect such convective dynamics. [9][10][11][12][13] In particular, it has been demonstrated theoretically [14][15][16][17][18][19][20][21][22][23] and experimentally 14,15,20,21,[24][25][26] that A + B -C type of chemical reactions can amplify or slow down convective fingering when all three species are in solution depending on their relative contribution to density. Reactions can therefore not only allow for the storage of larger amounts of CO 2 during convective dissolution because they consume CO 2 (reactive effect) but can also accelerate the development of convection (reaction-induced convective effects).…”

“…Reactions can therefore not only allow for the storage of larger amounts of CO 2 during convective dissolution because they consume CO 2 (reactive effect) but can also accelerate the development of convection (reaction-induced convective effects). 18 The two effects lead to larger dissolution fluxes of CO 2 , which contributes to a faster and safer storage. Therefore understanding the impact of chemical reactions on flow dynamics and how the dissolving fluxes scale with the parameters of the problem, mainly the Rayleigh numbers measuring the contribution of each chemical species to the density, and the ratio of the initial concentration of the reactants, is of tantamount importance.…”