Sensitivity analysis for a pumping test simulation with varying hydraulic parameter values and domain resolution

Abstract:

Groundwater flow simulation requires to determine the hydrogeological properties (e.g., hydraulic conductivity (K), porosity, and specific storage (S_s)), which dominate the flow system in the area of interest. Sensitivity analysis can be used to inspect how each hydraulic parameters affects the groundwater flow system. For the meanwhile, the degree of heterogeneity of the system is scale-dependent, and it can be realized by simulating while changing the resolution of the model domain. In this study, by changing the hydraulic parameters and domain resolution, we evaluated which parameters affect most the simulation results of a pumping test, which was conducted at the aquifer system of the Environmental Impact evaluation Test (EIT) facility of the Korea-CO₂ Storage Environmental Management (K-COSEM) research center. The simulation results were compared with those of the pumping test. The simulations were carried out using HydroGeoSphere (HGS), a three-dimensional groundwater-surface water integration model, and the simulated hydraulic heads were compared with those measured during the pumping test. Among the hydraulic parameters applied in this analysis, K and S_s were changed by 10^±1 and 10^±2 from the base case with 2.00×10^-5 m s^-1 for K_x and K_y, 2.00×10^-5 m s^-1 for K_z, and 1.54×10^-3 m^-1 for S_s, respectively. The porosity was changed by ±0.1 and ±0.2 from the base case with 0.3. The domain resolutions were changed by dividing the target area into 1, 8, and 27 blocks, respectively. When the resolution increased, the differences between the simulated and observed heads decreased in some simulation cases in which K and S_s were changed in particular zones. However, for the case of the model sensitivity to the porosity, even if the resolution of parametric zone is higher, there is no significant difference for the simulation results. Through this study, it is suggested that it is important to grasp the hydrogeological properties considering the heterogeneity with appropriate resolution in order to obtain accurate hydrogeological information for the underground space. This research was supported by the "R&D Project on Environmental Management of Geologic CO₂ Storage" from the KEITI (Project Number: 2018001810002).