Analysis on the reason for the higher volume shrinkage of Cavity A of Jintan salt-cavern gas storage

The Cavity A of Jintan Salt-Cavern Gas storage has been put into production for less than 2 years, but the sonar cavity test result shows that its volume shrinkage is 3.86%, which is about 5-7 times the average volume shrinkage of the other cavities in this area. In order to find out the reason for this excessive volume shrinkage, a 3D geomechanics model used for cavity stability evaluation was established based on stratigraphic structure, sonar cavity test data and monitored operation pressure in Jintan. Then, stability evaluation indexes were calculated and analyzed, including cavity volume shrinkage, cavity wall deformation, plastic zone, equivalent strain and dilation safety factor. It is indicated that the main reason for the excessive volume shrinkage is the sonar measurement error instead of the real volume shrinkage. The shape of this cavity is complicated with a great amount of hidden space, which increases the sonar measurement error. The cavity is overall more stable and its volume shrinkage is about 0.54%. The top structure of the cavity is flat with large span, which is not beneficial to the cavity top loading, so once it is damaged locally, instability damage (e.g. fallings from the top) will occur under the action of its dead weight and even the safety of the casing shoe will be threatened. Therefore, it is suggested to strengthen monitoring and control in the process of later operation.