Site selection and characterization for onshore 10,000-ton-class CO₂ pilot storage in Early Miocene Janggi Basin, SE Korea: Storage potential and structural stability of siliciclastic-volcaniclastic storage combination

This paper presents the results of site selection and characterization for onshore 10,000-ton-class CO₂ pilot storage in the Miocene Janggi Basin, SE Korea. The results were obtained from an integrated analysis of geological, geophysical, and geotechnical data, and indicated that Noeseongsan Subbasin is filled by >1-km-thick terrestrial sediments with dacitic to basaltic volcanic materials. Promising storage units are coarse siliciclastic sediments intercalated with mudstones in the lowermost Janggi Conlomerate, exhibiting suitable reservoir-caprock association for CO₂ injection. The overlying Seongdongri Formation is composed of laterally extensive dacitic tuffs and fine-dominated tuffaceous sediments, forming a regional seal. The storage combination is characterized by a doubly sealed stratigraphic trap, and is laterally confined by juxtaposed seals formed by syndepositional normal fault sets. By considering the stratigraphic and structural features, the conglomerate and sandstone bodies at the boreholes JG-6 (940−971 m) and JG-7−1 (946−970 m) were selected as the optimal site for CO₂ storage. It is expected that the stratigraphic and structural traps at the selected site minimize the leakage risk of injected CO₂ due to the scarcity of surface and subsurface fractures, low fault intensity, and limited vertical extents of buried faults. The present study reveals that if multidisciplinary approaches involving careful synthesis of the basin were performed, an adequate storage site also can be obtained in this type of small-scale ancient sedimentary basin bearing abundant volcanic materials.