Experimental study of density-driven convection effects on CO2 dissolution rate in formation water for geological storage

Permanent storage of CO2 in saline aquifers is known as one of the best methods for carbon dioxide sequestration. Understanding the role of convection in CO2 dissolution of saline aquifers – which affects the long-term fate of the injected CO2 and the security of storage – is extremely important. In this paper, two types of experiments are performed; first, visualization experiment in Hele–Shaw cell; and second, quantitative experiments at elevated pressure. These experiments are used to investigate the effect of Density-Driven Convection (DDC) on CO2 dissolution rate in saline aquifers. For this aim; first, visualization test is performed in a Hele–Shaw cell to observe convective instabilities and its effect on dissolution rate. Afterward, quantitative tests are performed, in which four parameters are calculated: Total Dissolution, Diffusion Dissolution (DD), Convection Dissolution (CD), and CO2 Convective Flux (FCO2). Through employing these parameters, the behavior of convection and its effects on CO2 dissolution rate based on the scaled experiments is shown, and two scaling relationships one between Rayleigh and Sherwood number and the other one between CO2 Convective Flux and Rayleigh number are developed. Such scaling relationships provide an estimation of the maximum convective dissolution of CO2 in saline aquifers which would be useful for assessing suitable CO2 storage sites.