## Materials and Methods  
### Sandstone Cores and Groundwater Samples  
Currently, South Korea is ranked seventh in the world in terms of CO\({}_{2}\) emissions, having produced a total of 739 megatons in 2011 alone [42], and the Korean government currently plans to inject more than 100 megatons of CO\({}_{2}\) into the subsurface by 2020 [43]. From a previous study, the Sindong lithost stratigraphic group of the Gyeongsang basin was considered as an available CO\({}_{2}\) storage site on the Korean peninsula (CO\({}_{2}\) storage capacity of 1011 megatons) [44]. In 2014, the Gyeongsang basin was announced as one of the candidate sites for a scCO\({}_{2}\) storage test in Korea, and continuous drill cores (4.2 cm of average diameter) were collected at two drilling sites (average 1200 m in depth). From the property analysis of these cores, three coarse sandstone formations (850, 1000, and 1050 m in depth) with medium porosity (porosity of 7.0%-9.8%) and moderate thickness (total of 100 m) were found, and their sandstone cores (S1, S2, and S3) were used for this study. A total of nine consolidated cylindrical sandstone cores (each 4.2 cm in diameter and 6-7 cm in length) without cracks or fractures were used to measure the physical and geochemical property changes of the cores during the scCO\({}_{2}\)-water-core reaction. For each sandstone core, several thin slabs (1 \(\times\) 1 \(\times\) 0.2 cm each) were additionally prepared to observe the surface roughness change and the cation concentration change for the whole reaction time. The geological map around the drilling site, the sandstone core, and the slab used for the experiment are shown in Figure 1. The mineral composition of each core was identifiedby modal analysis and more than 500 locations on each thin section surface were observed using the point counter attached in a polarizing microscope. The results of the modal analysis for the three cores (S1, S2, and S3) reveal that the sandstone surface is mostly composed of quartz, perthite, plagioclase, calcite, muscovite, biotite, and chlorite, and their average proportions were 47.4%, 18.5%, 10.5%, 5.4%, 1.7%, 1.5%, and 1.4%, respectively (Table 1). The surface roughness changes for these seven minerals were specifically targeted during the experiment. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Thin Section No.**} & \multicolumn{8}{c}{**Mineral Portion (\%)**} \\ \cline{2-10}  & **Quartz** & **Plagioclase** & **K-Feldspar** & **Muscovite** & **Biotite** & **Calcite** & **Chlorite** & **Others** \\ \hline S1-1 & 50.7 & 7.8 & 25.5 & 0.3 & 2.3 & 3.1 & 3.1 & 7.2 \\ S1-2 & 43.4 & 9.2 & 27.6 & 0.3 & 1.5 & 5.3 & 5.1 & 7.6 \\ S1-3 & 50.5 & 11.3 & 23.5 & 1.1 & 0.2 & 4.3 & 3.2 & 5.9 \\ S1-4 & 46.1 & 8.1 & 23.2 & 1.4 & 2.1 & 6.2 & 4.7 & 8.2 \\ Average \(\pm\) standard deviation & \(47.7\pm 3.6\) & \(9.1\pm 1.6\) & \(25.0\pm 2.0\) & \(0.8\pm 0.6\) & \(1.5\pm 0.9\) & \(4.7\pm 1.3\) & \(4.0\pm 1.0\) & \(7.2\pm 1.0\) \\ \hline S2-1 & 38.7 & 13.4 & 17.9 & 0.7 & 2.2 & 9.5 & 0.1 & 17.5 \\ S2-2 & 35.6 & 15.5 & 13.4 & 1.5 & 2.7 & 12.4 & 0.0 & 18.9 \\ S2-3 & 40.5 & 11.7 & 16.9 & 0.1 & 1.4 & 6.4 & 0.0 & 23.0 \\ S2-4 & 41.9 & 16.8 & 19.8 & 1.4 & 1.9 & 4.1 & 0.1 & 14.0 \\ Average \(\pm\) standard deviation & \(39.2\pm 2.7\) & \(14.4\pm 2.3\) & \(17.0\pm 2.7\) & \(0.9\pm 0.7\) & \(2.1\pm 0.5\) & \(8.1\pm 3.6\) & \(0.1\pm 0.1\) & \(18.4\pm 3.7\) \\ \hline S3-1 & 61.6 & 7.6 & 13.2 & 3.3 & 0.4 & 0.3 & 0.1 & 13.5 \\ S3-2 & 57.5 & 5.1 & 7.7 & 5.9 & 0.6 & 3.5 & 0.3 & 19.4 \\ S3-3 & 55.1 & 8.7 & 14.3 & 2.7 & 0.4 & 3.8 & 0.2 & 14.8 \\ Average \(\pm\) standard deviation & \(58.1\pm 3.3\) & \(7.1\pm 1.8\) & \(11.7\pm 3.5\) & \(4.0\pm 1.7\) & \(0.5\pm 0.1\) & \(2.5\pm 1.9\) & \(0.2\pm 0.1\) & \(15.9\pm 3.1\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Petrographic detridal modal analysis for sandstones. Figure 1: Geological map around the drilling site () and photographs of sandstone cores and a slab for the experiment (modified from [22]).