A numerical procedure for modeling the seepage field of water-sealed underground oil and gas storage caverns

Underground rock caverns have been considered as an effective technique for oil storage, commonly with water curtains for maintaining a desired and stable groundwater level and preventing the products from escaping. This study presents a three-dimensional analysis of groundwater flow in the surrounding rocks of water-sealed underground oil storage caverns. The water curtain consisting of numerous boreholes of small diameter, long extension and dense spacing is accurately modeled with a substructure technique. The influence of the oil vapor or mixed gas pressure in the caverns on the groundwater flow is considered by integrating it into the water head and complementary boundary conditions. The proposed method is applied to assess the performance of the water curtain system in the Huangdao oil storage caverns, the first-built underground oil storage project in China. The numerical results show that the gas pressure in the caverns leads to development of gas invasion zones around the cavern roofs, which decreases the thickness of the groundwater barrier and increases the risk of oil and oil vapor leakage. Based on the numerical observations, the design criteria for the water curtain system are discussed and modified.