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Effects of the geothermal gradient on the convective dissolution in CO2 sequestration
Published online by Cambridge University Press: 19 May 2023
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.
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