Stability evaluation of the underground gas storage in rock salts based on new partitions of the surrounding rock

Based on uniaxial and triaxial compression experiments, the yield, dilatancy and failure behaviors of the Jianghan rock salts were investigated. Accurate description of the yield and failure behaviors is helpful to reduce the space between storage caverns and offer more storage in a salt mine of limited extent. The experimental results showed that the yield function is a straight line and thus the Tresca yield criterion can be used to describe the yield behavior of the tested rock salt. The second invariant of the plastic strain was used as the hardening parameter to analyze the hardening behavior of the rock salt. The result shows that the rock salt is an isotropic hardening material. From the perspective of yielding, the rock salt acts like metals, while from the perspective of failure it acts like rocks. The dilatancy boundary was estimated in each experiment by determining the volume turnover point from compression to dilatation. It is found that the dilatancy boundary for the Jianghan rock salt is different from the results in the previous studies, especially under high stresses. Shear and splitting failures were observed in the compression tests. Splitting failure was analyzed based on the elastic theory for thick cylinders. The results indicate that failure depends on confining pressure. When the confining pressure is equal or greater than 5 MPa, the rock salt never breaks, even when the axial strain reaches 20 %. A no-broken condition was imported into the Mohr-Coulomb criterion. Based on the yield-dilatancy-failure model, the rock surrounding an underground gas storage (UGS) is divided into four zones: elastic, plastic, permeability and failure zone. A new stability criterion based on the partitions is proposed. The constitutive model was modified and the state parameters were self-defined in FLAC(3D). A geologic model for the Jianghan UGS was constructed to provide an example of the stability evaluation based on the partitions of the surrounding rock. The minimum internal pressure in emergency was also discussed for the Jianghan UGS.