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Salt caverns are internationally recognized as excellent facilities for underground energy storage. Creep shrinkage deformation will occur in deep salt caverns under the action of high-ground stress, and it is a key factor to evaluate the safety of salt caverns. However, there has been no salt cavern creep shrinkage mechanism research on ultra-deep salt caverns. In this paper, the creep shrinkage mechanism of an ultra-deep salt cavern is established from the theory, numerical simulation, and field application. First, the actual creep field experiments (pressure testing and sonar testing) of the salt cavern (depth ≥ 2000 m) are carried out. Second, theoretical models of salt cavern creep shrinkage are established from four influence aspects (creep shrinkage, heat conduction, salt dissolution, and brine permeability). Third, a 3D geological model is built to analyze the creep stability of deep salt caverns based on their field conditions. The novelty of this paper is analyzing the creep shrinkage of the ultra-salt cavern by the theoretical model, numerical model, and field experimental data systematically. The results show that the shrinkage of the salt cavern and brine thermal expansion is key factors leading to pressure lifting of the salt cavern, which accounts for 0.6121 and 0.2147 in the four influence aspects. Three creep phases are obtained: rapid rising stage, steady rising stage and decelerating rising stage. The study provides a reference for the creep shrinkage and field application of salt caverns. Highlights: Creep field experiments of the salt cavern are carried out. Theoretical models of ultra-deep salt cavern creep mechanisms are built. An ultra-deep 3D salt cavern creep numerical model is built to analyze the creep stability of salt caverns. A mathematical model is proposed to analyze the factors that influence salt cavern creep. [ABSTRACT FROM AUTHOR]

The mechanical properties and permeability of gypsum caprock have a significant influence on the tightness and stability of salt cavern gas storage, a series of tests were carried out to investigate the mechanical properties, permeability and AE characteristics of gypsum under THM coupling in this work. The peak strength of gypsum increases with the increase of confining pressure and the decrease of temperature, the failure and dilatation failure criteria are obtained by utilizing Mogi failure criterion. The permeability decreases with the increase of temperature in the compaction and linear elastic deformation stage, and the final permeability decreases with the increase of temperature under the confining pressure of 5 MPa and 15 MPa, while increase with the increase of temperature under the confining pressure of 25 MPa and 35 MPa. And the permeability decreases with the increase of confining pressure in the whole test process because of the constrain of confining pressure on the formation of microcracks and pores. The best fitting formulas of the relationship between permeability and confining pressure is given by fitting at 25 °C and 110 °C, which can be expressed by two exponential functions. The AE characteristics also confirmed that the increase of confining pressure and temperature inhibited the formation of microcracks and pores, and the AE peaks have the same hysteresis effect as the stress peaks. It is noted that the peaks of AE ring count increase with the increase of temperature under the confining pressure of 35 MPa. [ABSTRACT FROM AUTHOR]