Experimental Investigation on Permeability and Mechanical Properties of Cement–Salt Rock Interface Subjected to Cyclic Loading

The integrity of cement–salt rock interfaces (CSI) in salt cavern gas storage wells may be damaged during circulating gas injection, production, and long-term gas pressure maintenance. In this study, permeability tests were conducted on cement–salt rock samples under cyclic loading confining pressure at different holding times. The cracks and micro-annuli at the interface were visualised using X-ray computed tomography. The bonding strength of the interface after the permeability test was measured in a triaxial environment. The results showed that with an increase in the number of cycles, the cumulative volumetric strain rate and permeability first decreased rapidly and then tended to stabilise, and the decreasing amplitude was positively correlated with the holding time. When the holding times were 10, 30, and 60 min, the permeability change ratios were 0.844, 0.762, and 0.638, respectively, after one cycle and 0.722, 0.444, and 0.420, respectively, after five cycles. The permeability of CSI is mainly influenced by the holding time. The mechanical properties of the CSI specimens with similar permeabilities showed differences at different holding times. Cyclic loading easily degrades the mechanical properties, which can be improved by extending the holding time. The CSI is the main channel for gas leakage, extending the holding time, and increasing the number of cycles can effectively improve the pore structure of CSI and enhance the cement sheath integrity. This study provides a reference for long-term safe operation of salt cavern gas storage wells.