## Materials and Methods
### Measurement of the Surface Roughness Value for Sandstone Slabs  
The identification of the scCO\({}_{2}\)-rock-pore water geochemical reaction at scCO\({}_{2}\) sequestration conditions has been studied by various analytical processes. These approaches include qualitative processes mostly depending on visual inspection or compositional analysis using SEM/EDS (Scanning Electron Microscope/Energy Dispersive X-ray Spectrometer; VEGA II LSU, Tescan, Brno, Czech Republic), XRD (X-ray Diffractometer; X\({}^{\prime}\)Pert-MPD, Philips, Eindhoven, The Netherlands), and XRF (X-ray Fluorescence Spectrometer; XRF-1800, Shimadzu, Kyoto, Japan) [45; 46]. However, quantitative information acquired from this study was very limited, such as in mineral composition transfer and structural change [47; 48]. To supplement these limitations, the surface roughness change of the rock surface during the scCO\({}_{2}\)-sandstone-groundwater reaction was investigated, and the feasibility of its use as a parameter to evaluate the geochemical weathering process was verified by comparing the physical property change of the sandstone with the cation concentration change in groundwater during the geochemical reaction. To observe the surface roughness change of the slab surface over the reaction time, one surface of each slab prepared from the sandstone core was polished with diamond-coated paper and the other slab surface was attached to a glass slide plate with epoxy resin. After being washed with methanol, each thin slab was placed at the bottom of a Teflon beaker, which was fixed inside a high pressurized stainless steel cell (with a capacity of 150 mL), and 100 mL of groundwater was poured into the Teflon beaker. The inside of the cell was pressurized up to 100 bar using a high-pressure syringe pump (Isco-D260, TELEDYNE ISCO, Lincoln, NE, USA) and the empty space in the cell was filled with scCO\({}_{2}\) by a gas flow regulator attached to a high-pressure syringe pump. Each cell was placed in an oven to maintain a constant temperature of 50 \({}^{\circ}\)C, which led to a scCO\({}_{2}\)-rock-groundwater reaction in the cell at scCO\({}_{2}\) sequestration conditions. The scCO\({}_{2}\)-sandstone slab-groundwater reaction in the cell was executed at 100 bar and 50 \({}^{\circ}\)C for 150 days and the apparatus of the slab experiment is shown in Figure 2. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Temp. (\({}^{\circ}\)C)**} & \multirow{2}{*}{**pH**} & \multicolumn{8}{c}{**Average Concentration (mg/L)**} \\ \cline{3-13}  & & **Na\({}^{\star}\)** & **Ca\({}^{\star}\)** & **K\({}^{\star}\)** & **Mg\({}^{\star}\)** & **Si\({}^{\star}\)** & **Al\({}^{\star}\)** & **Fe\({}^{\star}\)** & **Cl\({}^{-}\)** & **SO\({}_{4}\)\({}^{\text{2}-}\)** & **NO\({}_{3}\)\({}^{\text{}-}\)** & **HCO\({}_{3}\)\({}^{-}\)** \\ \hline
40.6 & 8.6 & 633.2 & 547.1 & 23.3 & 20.9 & 12.4 & 4.3 & 0.0 & 2109.1 & 259.3 & 212.0 & 51.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Temperature, pH, and chemical composition of groundwater used in the experiment. Figure 2: Apparatus used for the slab experiment to simulate the scCO\({}_{2}\)-sandstone-groundwater reaction. According to previous studies related to geochemical reactions, the weathering process of the reservoir rock after scCO\({}_{2}\) injection was closely related to the surface roughness change of the rock because dissolution and precipitation occur simultaneously and lead to surface roughness change until the geochemical system turns back to a status of equilibrium [22; 49]. To observe the surface roughness change of sandstone slabs during the geochemical reaction, seven minerals, quartz, perthite, plagioclase, muscovite, calcite, biotite, and chlorite for each slab surface were determined using a reflecting microscope (Nikon eclipse LV100N, Nikon, Fukasawa, Japan), and three locations for each mineral were randomly selected to acquire 3-dimensional surface images. Each slab was taken out from the cell and dried in an oven at certain reaction time intervals.