MIGRATION AND TRAPPING PHENOMENA OF BUOYANCY-DRIVEN CO2 IN WATER-SATURATED POROUS MEDIA USING LATTICE BOLTZMANN METHOD

CO2 geological sequestration is an immediately available and technologically feasible method for substantially reducing CO2 emissions into the atmosphere. However, the buoyancy-driven migration of CO2 in an aquifer is still an important issue for the evaluation of storage sites and the assessment of CO2 leakage risks and storage costs. In this study, the buoyancy-driven CO2 migration process is studied with the lattice Boltzmann method, with the advantage of modeling two-phase flow in porous media. The dynamic migration and trapping process of a CO2 bubble is studied microscopically, and bubble behaviors are evaluated by capillary pressure. The migration process associated with snap-off is also discussed. Initially large volumes of CO2 migrate upward, accompanied by snap-off phenomena caused by small fluctuations of slice-averaged porosity. The buoyancy effect of the CO2 plume is divided by the snap-off, and ultimately all CO2 is stably trapped in the porous media by the capillary effect. The CO2 trapping condition is addressed by defining Bond number Bo, and Bo', and the relation between pore throat structure and trappable CO2 height is explained.