Sensitivity Study of Simulation Parameters Controlling CO_2 Trapping Mechanisms in Saline Formations

摘要

The primary purpose of this study is to understand quantitative characteristics of mobile, residual, and dissolved CO_2 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), maximum residual CO_2 saturation (S_(gr)~(max)), and brine density (p_(br))- Simulation results indicate that residual CO_2 trapping increases proportionally to k_v, k_h, S_(gr)~(max) and ρ_(br) but is inversely proportional to φ. In addition, the amount of dissolution-trapped CO_2 increases with k_v and k_h, but does not vary with φ, and decreases with S_(gr)~(max) and ρ_(br)- Additionally, the distance of buoyancy-driven CO_2 migration increases proportionally to k_v and ρ_(br) only and is inversely proportional to k_h,φ, and S_(gr)~(max). These complex behaviors occur because the chosen sensitivity parameters perturb the distances of vertical and horizontal CO_2 plume migration, pore volume size, and fraction of trapped CO_2 in both pores and formation fluids. Finally, in an effort to characterize complex relationships among residual CO_2 trapping and buoyancy-driven CO_2 migration, we quantified three characteristic zones. Zone I, expressing the variations of S_(gr)~(max) and k_h, represents the optimized conditions for geologic CO_2 sequestration. Zone II, showing the variation of 0, would be preferred for secure CO_2 sequestration since CO_2 has less potential to escape from the target formation. In zone III, both residual CO_2 trapping and buoyancy-driven migration distance increase with k_v and ρ_(br).