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Dissolution-driven convection in partially miscible systems has regained much interest in the context of CO$_2$ sequestration [1]. A buoyantly unstable density stratification can build upon dissolution of CO$_2$ into brine, thereby driving convection. Dissolution and convection are known to improve the safety of the sequestration process by reducing the risks of leaks of CO$_2$ to the atmosphere. The temporal evolution of dissolution-driven convective dynamics has been characterized in detail and it has been shown that the dissolution flux reaches a steady-state value before shutdown [2]. The question remains, however, as to how the efficiency of such process depends on the chemical properties of the storage site and how chemical reactions can affect the steady-state fluxes. Reactions can indeed accelerate or slow down the development of dissolution-driven convection in partially miscible stratifications when they impact the density profile in the host fluid phase. The different possible dynamics taking place during the convective dissolution of CO$_2$ into a host fluid containing a dissolved reactant B have been classified for a chemical reaction CO$_2$ + B $\rightarrow$ C (product), assuming that all species diffuse at the same rate [3,4]. We now consider the more general case where solutes can diffuse at different rates. Using nonlinear simulations, we show that depending on the type of density profile developing in the host fluid, one or two convection zones can be observed. Although changing the diffusivity ratios can have non-trivial effects, decreasing the diffusion coefficient of product C or increasing the diffusion coefficient of reactant B both accelerate the development of convection and amplifies the global reaction rate in the host solution. Both effects contribute to a larger dissolution flux and a faster storage of CO$_2$ into the host fluid. We compare our results with experimental results showing that reactions accelerate the development of buoyancy-driven fingering during the convective dissolution of CO$_2$ into aqueous reactive solutions of alkali hydroxides [5].
[1] A. Firoozabadi and P. Cheng, Prospects for subsurface CO$_2$ sequestration, AIChE Journal 56, 1398 (2010).
[2] H. Emami-Meybodi, H. Hassanzadeh, C. P. Green, and
J. Ennis-King, Convective dissolution of CO$_2$ in saline aquifers: Progress in modeling and experiments, International Journal of Greenhouse Gas Control 40, 238 (2015).
[3] V. Loodts, C. Thomas, L. Rongy, and A. De Wit, Control of convective dissolution by chemical reactions: General classification and application to CO$_2$ dissolution in reactive aqueous solutions, Physical Review Letters 113, 114501 (2014).
[4] V. Loodts, B. Knaepen, L. Rongy, and A. De Wit, Enhanced steady-state dissolution flux in reactive convective dissolution, Physical Chemistry Chemical Physics 19, 18565 (2017).
[5] C. Thomas, V. Loodts, L. Rongy, and A. De Wit, Convective dissolution of CO$_2$ in reactive alkaline solutions: Active role of spectator ions, International Journal of Greenhouse Gas Control 53, 230 (2016).
References
[1] A. Firoozabadi and P. Cheng, Prospects for subsurface CO$_2$ sequestration, AIChE Journal 56, 1398 (2010).
[2] H. Emami-Meybodi, H. Hassanzadeh, C. P. Green, and
J. Ennis-King, Convective dissolution of CO$_2$ in saline aquifers: Progress in modeling and experiments, International Journal of Greenhouse Gas Control 40, 238 (2015).
[3] V. Loodts, C. Thomas, L. Rongy, and A. De Wit, Control of convective dissolution by chemical reactions: General classification and application to CO$_2$ dissolution in reactive aqueous solutions, Physical Review Letters 113, 114501 (2014).
[4] V. Loodts, B. Knaepen, L. Rongy, and A. De Wit, Enhanced steady-state dissolution flux in reactive convective dissolution, Physical Chemistry Chemical Physics 19, 18565 (2017).
[5] C. Thomas, V. Loodts, L. Rongy, and A. De Wit, Convective dissolution of CO$_2$ in reactive alkaline solutions: Active role of spectator ions, International Journal of Greenhouse Gas Control 53, 230 (2016).
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