Effects of the geothermal gradient on the convective dissolution in CO<sub>2</sub>sequestration
C.Y. Hu, Ke Xu, Yantao Yang
Abstract
Convective dissolution is an important mechanism for long-term CO $_2$ sequestration in deep saline aquifers. The presence of an unstable geothermal gradient can affect the process of dissolution. In this paper, we present direct numerical simulations in a three-dimensional porous medium at three different concentration Rayleigh numbers $Ra_S$ with a set of thermal Rayleigh numbers $Ra_T$ . Simulations reveal that the flow structures alter when ${\textit {Ra}}_T$ increases for a fixed ${\textit {Ra}}_S$ . Strong thermal gradient can yield large-scale convection rolls which change the horizontal distribution and motions of concentration fingers. The time evolution of fluxes also has different responses to different ${\textit {Ra}}_T$ . A theoretical model is developed and successfully describes the evolution of concentration flux and volume averaged concentration during the final shutdown stage. We further calculate the dissolved CO $_2$ into the interior over time, which shows non-monotonic variations as ${\textit {Ra}}_T$ increases. At the end of our simulations, the maximum increment of dissolved CO $_2$ occurs when density ratio is around unity for all three concentration Rayleigh numbers we have explored. We apply our results to a typical geological reservoir and discuss their implications.