Density Driven (Including Geothermal Effect) Natural Convection of Carbon Dioxide in Brine Saturated Porous Media in the Context of Geological Sequestration

Abstract

Double diffusive natural convection of carbon dioxide in two-dimensional cavities filled with brine saturated porous media is numerically investigated in this study. Vertical gradients of carbon dioxide concentration and temperature are imposed across the height of the cavity. The objective is to understand the dissolution of carbon dioxide through natural convection process over long period of time after sequestration into subsurface porous media aquifer. The problem parameters are the solutal Rayleigh number (Ras = 100 to 10000), the buoyancy ratio (N = 2 to 100), the thermal Rayleigh number (RaT = 2 to 100), the cavity aspect ratio (A = 0.5 to 2), and a fixed Lewis number (Le = 301). It is found that the CO2 plumes move faster when Ras is increased, however slow down with decreasing N. For every simulation run, the average CO2 dissolution in the reservoir is computed. At early stage (within 10 years) of the convection process, the CO2 dissolutions are same for all cases studied. After 500 years the dissolution is found to be around 0.63 for N = 100, and around 0.47 for N = 2, respectively. After 2000 years the dissolution rate is extremely slow. When the reservoir aspect ratio (A) is changed, the dissolution rate changes slightly. The rate is slightly higher in laterally wide reservoir, which makes it better candidate than the deeper aquifer from the context of CO2 sequestration.