Three-Dimensional Visualization of Natural Convection in Porous Media

Abstract

Carbon dioxide (CO2) geological storage (CGS) is a preferred technique to mitigate anthropogenic climate change. In terms of CGS, density-driven natural convection dominated dissolution of CO2 into formation brine results in a stable trapping increasing the storage security.A full utilization of a nonlinear density property of fluid system has been applied to mimic the natural convection in saline aquifers. Three-dimensional natural convection in porous medium has been observed by employing X-ray computer tomography (CT) technology. Since the X-ray attenuation depends on the concentration of sodium iodide, the distribution of local concentration can be evaluated during the downward extension based on the CT images.We successively visualized the process of formation and the development of Rayleigh-Bénard fingers. This process modelled natural convection between heavier CO2 loaded brine and brine with little (or no) CO2. High density fingers extend downward at the characteristic buoyancy velocity and coalescent with the neighbouring finger before reaching the bottom of the porous medium. The coalescence of fingers leads to a decrease in finger number and an increase in finger diameter. As the Rayleigh number increases, the finger tends to be fine and extends faster. The mass transfer rate increases with the Rayleigh number also.