The Effect of Cyclic Storage and Release Process on the Integrity of Rock Salt in Salt Cavern Hydrogen Storage

In the context of increasing demand for large-scale geological hydrogen storage, maintaining the integrity and sealing performance of salt caverns under cyclic gas storage and release conditions remains a critical engineering challenge. This study presents a laboratory-based experimental investigation into the effects of cyclic storage–release operations on the permeability and structural integrity of rock salt. A custom-designed testing system was developed by integrating a Programmable Logic Controller (PLC) unit into a commercial rock mechanics testing apparatus, enabling real-time monitoring of equivalent permeability and internal damage evolution. Using helium as a surrogate gas, repeated pressurization–depressurization cycles were applied to cylindrical salt samples extracted from the Jintan area in China. Permeability was measured using the pulse decay method, and microstructural damage was assessed via X-ray computed tomography (CT). Results show a noticeable decrease in permeability after 100 cycles, with no order-of-magnitude change after 200 cycles, indicating strong self-healing characteristics of rock salt under low pressure range. Microcrack development was mainly confined to borehole ends, while the bulk material remained largely intact. These findings validate the suitability of salt caverns for hydrogen storage and provide valuable insights for the safe design and operation of underground energy storage systems.