## 3 Results and Discussion  
### Spatial Properties Influencing CO\({}_{2}\) Trapping  
DGSA parameters are assigned as follows: k-medoid clustering, with six clusters, classifies 1024 aquifer models and the resampling quantile of distance is 0.95. A response for DGSA is the trapping volume of combined structural and residual trapping, representing relatively permanent and safe sequestration. The trapping amount is a cumulative volume during 200 years from the first injection. Six uncertain parameters (C = 6 in Equation (2)) are mean sandstone porosity, mean sandstone permeability, standard deviation of sandstone porosity, standard deviation of sandstone permeability, shale volume ratio, and Dykstra-Parsons coefficient, respectively (\(m=6\) in Equation (2); Table 1). To remove the effects of well allocation, a constant injection rate, 4000 m\({}^{3}\)/day for each injector is assumed. Total injection rate per day is 16,000 m\({}^{3}\)/day because four injectors are placed (Figure 1a). CO\({}_{2}\) is injected continuously for 30 years and the trapping trend is monitored for 200 years, i.e., an additional 170 years from the end of CO\({}_{2}\) injection.  
Figure 3 depicts the result of DGSA with spatial parameters; the sensitive parameters are the mean porosity of sandstone (PoroSand), mean permeability of sandstone (PermSand), shale volume ratio (SVR), and Dykstra-Parsons coefficient (VDP) in each row. The vertical line (the standardized sensitivity = 1; the significant level) indicates whether the parameter influences the response. The larger standardized sensitivity means more influence. The sensitive parameters support the importance of heterogeneity and aquifer properties on CO\({}_{2}\) trapping: PoroSand determines the capacity size, PermSand affects CO\({}_{2}\) mobility, SVR and VDP represent the effects of the shale barrier on storage and transport, respectively. The trapping amounts significantly depend on the pore volume of sandstone. The other parameters over the significant level are closely related to CO\({}_{2}\) flow. With increasing SVR and VDP, shale is likely to obstruct CO\({}_{2}\) flow. However, this would be a subject of discussion as to whether the large amount of shale always has a positive effect on the trapping volume. The asymmetric parameter interactions can make this debate more complicated as a parameter can simultaneously influence the different responses. If the operating conditions are included, deriving a reasonable conclusion would become a conundrum.  
Figure 3: DGSA result. The abbreviations of spatial parameters are in Table 1. PoroSand, PermSand, SVR, VDP, StdPoro, and StdPerm represent the mean porosity of sandstone, the mean permeability of sandstone, shale volume ratio, Dykstra–Parsons coefficient, the standard deviation of sandstone porosity, and the standard deviation of sandstone permeability, respectively. The Pareto bars are colored according to the percentile values. The horizontal black line represents confidence interval within a parameter that is still accepted as influencing. The vertical line means the significant level (if the standardized sensitivity is greater than 1, it means that the parameter is sensitive to the response).