Assessment of seawater intrusion into underground oil storage cavern and prediction of its sustainability

Abstract

Operation of underground oil (gas) storage cavern in coastal area can induce seawater intrusion because excavation of underground storage cavern causes the groundwater level decrease of coastal aquifer. Seawater intrusion has the potential to cause the corrosion of underground cavern facility and leakage of gas and oil from the storage caverns, therefore, seawater intrusion into the underground storage caverns should be evaluated carefully to avoid unexpected operation problems. In this study, the extent of seawater intrusion into underground oil storage cavern in Yeosu, Korea, was assessed through field monitoring and numerical modeling to evaluate the storage cavern sustainability against seawater intrusion. The mean values of seawater mixing ratios of seepage water in each cavern, estimated through modeling, range from 0.01 to 8.70 %, which are less than the measured mixing ratio (2.3–12.8 %) based on the Cl− concentrations. This result indicates that other source of Cl− may have contributed to the observed salinity in the cavern seepage water. Spatial and temporal variations in monitoring data and numerical modeling demonstrate that the location of storage, seepage water flow rate, and the fracture zones are important factors controlling seawater mixing ratio. Seawater intrusion barrier wells located along the coastline were shown to be important to prevent seawater intrusion into the storage caverns significantly. The predicted seawater mixing ratio after 100 years of cavern operation is 0.06–12.7 % varying depending on the caverns’ location.