CO2 Trapping Phenomena in Porous Media of Geological Storage by Lattice Boltzmann Method
The geological storage of carbon dioxide (CO2) will be vital in achieving future reductions in CO2 emissions. Deep saline aquifers are major candidate sites for CO2 sequestration, because of their enormous storage potentials. However, buoyancy-driven migration of CO2 in an aquifer is still an important issue in the evaluation of storage sites and assessment of CO2 leakage risks and storage costs. Many studies have focused on imbibition or drainage phenomena; however, buoyancy-driven flow and dynamic behavior of CO2 on the micro-scale were not addressed, because real-time experimental observation was quite difficult. 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. With the advantage of the LBM, the dynamic migration and trapping process of a CO2 droplet is studied microscopically, and droplet behaviors are evaluated by capillary pressure. CO2 size was mimicked by varying the gravitational coefficient. 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 CO2 bubbles are 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.