DENSITY DRIVEN (INCLUDING GEOTHERMAL EFFECT) NATURAL CONVECTION OF CARBON DIOXIDE IN BRINE SATURATED POROUS MEDIA IN THE CONTEXT OF GEOLOGICAL SEQUESTRATION

摘要

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 (100 ≤ Ra_s ≤ 10000), the buoyancy ratio (2 ≤ N ≤ 100), the thermal Rayleigh number (2 ≤ Ra_T ≤ 100), the cavity aspect ratio (0.5 ≤ A ≤ 2), and a fixed Lewis number (Le = 301). It is found that the CO_2 plumes move faster when Ra_s is increased, however slow down with decreasing N. For every simulation run, the average CO_2 dissolution (S = ∑ from i to n_i and ∑ from j to n_j of c_(i,j)/n_i×n_j) in the reservoir is computed. At early stage (≤10 years) of the convection process, the CO_2 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 CO_2 sequestration.