Sensitivity Study of Simulation Parameters Controlling CO₂ Trapping Mechanisms in Saline Formations

The primary purpose of this study is to understand quantitative characteristics of mobile, residual, and dissolved CO₂ trapping mechanisms within ranges of systematic variations in different geologic and hydrologic parameters. For this purpose, we conducted an extensive suite of numerical simulations to evaluate the sensitivities included in these parameters. We generated two-dimensional numerical models representing subsurface porous media with various permutations of vertical and horizontal permeability (k_v and k_h), porosity (φ{symbol}), maximum residual CO₂ saturation (S_gr^max), and brine density (ρ_br). Simulation results indicate that residual CO₂ trapping increases proportionally to k_v, k_h, S_gr^max and ρ_br but is inversely proportional to φ{symbol}. In addition, the amount of dissolution-trapped CO₂ increases with k_v and k_h, but does not vary with φ{symbol}, and decreases with S_gr^max and ρ_br. Additionally, the distance of buoyancy-driven CO₂ migration increases proportionally to k_v and ρ_br only and is inversely proportional to K_h, φ{symbol} and S_gr^max. These complex behaviors occur because the chosen sensitivity parameters perturb the distances of vertical and horizontal CO₂ plume migration, pore volume size, and fraction of trapped CO₂ in both pores and formation fluids. Finally, in an effort to characterize complex relationships among residual CO₂ trapping and buoyancy-driven CO₂ migration, we quantified three characteristic zones. Zone I, expressing the variations of S_gr^max and k_h, represents the optimized conditions for geologic CO₂ sequestration. Zone II, showing the variation of φ{symbol}, would be preferred for secure CO₂ sequestration since CO₂ has less potential to escape from the target formation. In zone III, both residual CO₂ trapping and buoyancy-driven migration distance increase with k_v and ρ_br.