*2.1. Preparation of the scCO2 Reservoir and Capping Rock Cores*

From the well logging data for four drilling sites in the Janggi Basin, rudaceous sandstone and conglomerate layers were considered available CO2 storage sites and the dacitic tuff and mudstone layers overlaying them as suitable cap rock [8,9]. Continuous drill cores (4.2 cm average diameter) from a drilling site 1200 m deep were acquired from KIGAM. From property analysis of these cores, three rudaceous sandstone cores (JG1-S1, JG1-S2, and JG1-S3; from 930–950 m) and three conglomerate cores (JG1-C1, JG1-C2, and JG1-C3; from 950–980 m) with average porosity of 14–18% were found and they were used for measurement of the scCO2 storage ratio. For the sealing cap rock, three mudstone cores (JG1-M1, JG1-M2, and JG1-M3; from 700–760 m) and three tuff cores (JG1-T1, JG1-T2, and JG1-T3; from 800–810 m) were used for the measurement of the initial scCO2 capillary entry pressure. Each rock core used in the experiment was cylindrical without cracks or fractures (4.2 cm diameter; length 5–7 cm). The geological map showing the area around the drilling site in the Janggi Basin and the rock cores used for the experiments are shown in Figure 1.

The CO2 storage and sealing capacity of rocks depend on physico-chemical properties such as porosity, permeability, reaction rate, and mineralogical stability. The porosity of the rock cores was measured using the vacuum saturation method suggested by the International Society for Rock Mechanics (ISRM) with vacuum pressure of 1 torr and vacuum time of 80 min. For each sandstone and conglomerate core, several thin slabs (1 cm × 1 cm × 0.2 cm each) were also prepared to identify the mineral composition of each core by modal analysis. To quantify the average mineral portion of

each reservoir rock, 500 locations on each thin section surface of each rock slab were observed using a point-counter installed in a polarizing microscope. For each mudstone and tuff core, mineralogical and geochemical analyses were performed using XRD (X-Ray Diffractometer; X'Pert-MPD, Philips, Almelo, The Netherlands) and XRF (X-Ray Fluorescence Spectrometer; XRF-1800, Shimadzu, Kyoto, Japan), to determine their mineralogical properties.

**Figure 1.** Geological map of the area around the drilling site (JG-1: ) in the Janggi Basin, Korea, photographs of rock cores used for the experiment and the stratigraphic columnar section (from left to right) used for the experiment (modified from [7,8]).
