Investigation of ground condition changes due to cryogenicconditions in an underground LNG storage plant

To investigate the feasibility of a new concept of storingLiquefied Natural Gas (LNG) in a lined hard rock cavern, and todevelop essential technologies for constructing underground LNGstorage facilities, a small pilot plant storing liquid nitrogen (LN2)has been constructed at the Korea Institute of Geoscience andMineral Resources (KIGAM). The LN2 stored in the cavern willsubject the host rock around the cavern to very low temperatures, which is expected to cause the development of an ice ring andthe change of ground condition around the storage cavern. Toinvestigate and monitor changes in ground conditions at this pilotplant site, geophysical, hydrogeological, and rock mechanicalinvestigations were carried out. In particular, geophysical methodsincluding borehole radar and three-dimensional (3D) resistivitysurveys were used to identify and monitor the development of anice ring, and other possible changes in ground conditions resultingfrom the very low temperature of LN2 in the storage tank. Weacquired 3D resistivity data before and after storing the LN2, andthe results were compared. From the 3D images obtained duringthe three phases of the resistivity monitoring survey, we delineatedzones of distinct resistivity changes that are closely related tothe storage of LN2. In these results, we observed a decrease inresistivity at the eastern part of the storage cavern. Comparing thehydrogeological data and joint patterns around the storage cavern, we interpret this change in resistivity to result from changesin the groundwater flow pattern. Freezing of the host rock bythe very low temperature of LN2 causes a drastic change in thehydrogeological conditions and groundwater flow patterns in thispilot plant.