Salt cavern gas storage in an ultra-deep formation in Hubei, China

The target formation of Jianghan salt district, Qianjiang city, Hubei province, China, for underground gas storage (UGS) construction has a depth of more than 1800 m. The cavern will be the deepest salt cavern UGS in Asia. A 3D geomechanical model of the proposed salt cavern UGS is built based on the geologic characteristics and mechanical parameters of the target formation. A new indexes system composed of displacement, volume shrinkage, plastic zone, dilatancy safety factor, and equivalent strain is proposed to quantitatively evaluate the safety of Jianghan salt cavern UGS. The thresholds of each indicator are proposed based on the characteristics of rock salt in China. By using the proposed indexes system, the cavern shape, dimensions, operating parameters and pillar width are optimized. Calculating results show that the optimized cavern has a slender cylindrical shape with a domed roof and an inverted cone bottom; its diameter ranges from 80 to 90 m, its height is about 210 m, and its free volume (accessible to gas) is about 50-65×104 m3. The maximum operating gas pressure is about 34 MPa, and the minimum gas pressure is no less than 17 MPa. The width of the pillar between adjacent caverns is about 2.5-3 times the cavern diameter. The gas storage capacity of a single cavern is about 1.1×109 m3, and the working gas is about 0.7×109 m3, which is about three times that of a single cavern in Jintan salt cavern UGS, Jiangsu province, China. The results indicate that Jianghan salt cavern UGS has a good feasibility for large-scale gas storage.