A novel operational parameters optimizing method for ultra-deep high-impurity salt cavern gas storage

Utilising sediment void space for gas storage represents a significant development direction for sediment-type salt cavern gas storage (SCGS). This study is based on an engineering context involving an ultra-deep salt layer (1800∼2000 m) with thick interlayers in Jiangsu Province. Firstly, a continuous medium mechanical model accounting for sediment compression effects was established. Subsequently, a 3D geological model built based on the field conditions and proposed mechanical model, and four numerical simulation schemes were designed with different lower operating pressure thresholds of 0.3 σH, 0.4 σH, 0.45 σH, and 0.5 σH, as well as scenarios with and without sediment. Finally, the Matter-Element Extension Method was employed to quantitatively classify the stability grades of the SCGS. Results indicate that at the 0.45 σH with sediment present, the volume shrinkage rate is 14.84%, and the maximum displacement is 5.37 m. Stability of 0.3 σH and 0.4 σH groups are at T5 level (unstable), the 0.45 σH group is at T2 level (stable), and the 0.5 σH group is at T1 level (very stable) through the method. This study can provide reference for the design and safe operation of sediment-type SCGS under similar complex geological conditions.