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Convective dissolution of CO2 in reactive alkaline solutions: Active role of spectator ions

par Thomas, Carelle ;Loodts, Vanessa ;Rongy, Laurence ;De Wit, Anne
Référence International Journal of Greenhouse Gas Control, 53, page (230-242)
Publication Publié, 2016

Article révisé par les pairs

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Résumé :

Upon dissolution of carbon dioxide (CO2) into deep saline aquifers, various chemical reactions are likelyto take place between dissolved CO2and reactants dissolved in the brine, which may drastically impactthe mixing of stored CO2in the reservoir. Our objective is to understand how the nature of the dissolvedchemical reactants affects the convective dynamics generated by the dissolution of CO2into the hostphase. To do so, we study experimentally in a Hele-Shaw cell the reactive and convective dissolution ofgaseous CO2into aqueous solutions of bases MOH where M+is an alkali metal cation. We quantify theeffect of the counter-ion M+on the convective dynamics. Using a schlieren optical setup, we compare theconvective patterns in pure water to those in different alkaline solutions of various concentrations. Forany reactant MOH studied, the fingering instability develops faster in the reactive case than in pure water,and convection is enhanced if the concentration of the reactant is increased. Furthermore, changing thecounter-ion M+modifies the onset time and the non-linear development of the fingering instability.We explain these experimental results by theoretically analyzing the reaction–diffusion density profilesdeveloping in the solution. We find that changing the counter-ion M+of the base modifies the densityprofile, not only through solutal effects but also through differential diffusivity effects. This highlightsthat the spectator ion M+, despite not participating actively in the acid–base reaction, impacts the devel-opment of the hydrodynamic instability. Our results suggest that, in the context of CO2sequestration, thedetails of the chemical composition of the storage site should be taken into account for more accuratemodeling of the reactive transport of dissolved CO2.