Assessment of Geological Storage Potential of Carbon Dioxide in the Miocene Pohang Basin, SE Korea

Abstract:

The goal of this study is to assess geological storage potential of CO₂ in the Miocene Pohang Basin, based on the structural and stratigraphic characteristics with the hydraulic features of the basin-fill and depth distribution of the basement. The basin is a pull-apart basin extended due to NNW-trending dextral strike slip faulting. The western margin of the basin consists of a series of segmented NNE-trending normal faults divided by NNW- or NW-trending dextral strike-slip faults. The southern margin is Yeonil Tectonic Line that is a zigzag-shaped NNW-trending fault zone consisting of NNW-trending dextral strike-slip and NNE-trending normal fault segments. The line connects with the NNE-trending western border faults with an oblique 50° angle. The Ocheon Fault System (OFS), the eastern marginal fault of the basin, is a NE-trending relayed fault system composed of a number of NE or NNE-trending normal-slip and sinistral-normal oblique-slip faults, and has a scissor fault geometry decreasing in vertical offset southwestward. The OFS which acted as initially normal fault experienced clockwise rotation with change of slip sense from normal-slip to sinistral-normal oblique-slip in response to a progressive dextral simple shear. The geometry and kinematics of syndepositional structures as well as the marginal faults indicate a WNW-ESE horizontal minimum stress. Stratigraphic and sedimentologic investigations suggest that dramatic subsidence of the hanging-wall of the western border faults resulted in thick accumulation of fan-delta successions and intervening and/or overlying hemipelagic mudstones. In addition, this study reveals that there are a number of NNE-trending normal faults dipping toward the east inside the basin. Depth distribution of the basement through deep drilling boreholes also supports the existence of the normal faults. These results thus indicate that potential geologic CO₂ storage sites in the Pohang basin are located on the easternmost part of the basin along the east coast line. The several columns of the boreholes also show that high porous and permeable coarse sedimentary rocks occur in the depth of 700-900 m, which are overlain by thick low-permeable mudstones. They are thus significantly eligible to be a major reservoir body for CO₂ underground storage.