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Chemical reactions control convective dissolution in porous media

par Loodts, Vanessa ;Rongy, Laurence ;De Wit, Anne
Référence Cargèse Summer School on Flow and Transport in Porous and Fractured Media: Development, Protection, Management and Sequestration of Subsurface Fluids (2015: Cargèse, France)
Publication Non publié, 2015-07

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Résumé :

In partially miscible systems, one phase dissolves into a host phase with a finite solubility. Even if the situation is initially buoyantly stable with the less dense dissolving phase on top of the denser host one, an unstable density stratification can develop in time in the gravity field if the density of the host phase increases upon dissolution. The development by dissolution of a denser layer below the interface leads to buoyancy-driven convection in the host phase, which accelerates the transport of the dissolving species and thus the mixing of the two phases compared to the pure diffusive case. This situation arises for example during carbon dioxide (CO2) sequestration in geological storage sites, where CO2 dissolves into brine or oil, increasing thereby their density. Chemical reactions can affect the density stratification since the dissolved CO2 can react with minerals present in the storage site. It has been shown that a reaction of CO2 with the porous solid matrix slows down the development of convection because the reaction consumes the dissolving species, thereby reducing the extent of the denser layer at the origin of the instability. In our study, we show that a reaction between the dissolving species and a dissolved reactant can either accelerate or slow down the development of convection, depending on the type of density profile building up in time in the reactive solution. With a linear stability analysis of a reaction-diffusion-convection model, we classify the effect of reactions on convective dissolution in a parameter space spanned by the contributions of the different species to the density of the host phase. Previous experimental and theoretical works fit into this classification.