Stability assessment of CAES salt caverns using a fractal-order derivative creep-fatigue damage model

Compressed air energy storage (CAES) presents a promising solution for large-scale energy storage, effectively mitigating the intermittency and variability challenges inherent in integrating renewable energy sources into the electric grid. This study investigates the long-term stability of a U-shaped CAES salt cavern in Huai'an, China. A 3D geomechanical model was developed, incorporating a novel fractal-order derivative creep-fatigue damage (FDCFD) model to accurately characterize the long-term mechanical behavior of the rock salt. The study indicated that increasing both the upper and lower operating pressure limits effectively reduces cavern displacement and volume shrinkage, with the lower limit demonstrating a more pronounced effect. Maintaining a constant midpoint between the upper and lower operating pressures while increasing the cyclic pressure amplitude significantly enhances gas storage capacity per unit volume at the expense of slightly increased volume shrinkage. Conversely, reducing the frequency of injection and withdrawal cycles effectively minimizes both displacement and volume shrinkage. Both the plastic zone volume and volume shrinkage demonstrate a negative correlation with pressure variations, accompanied by some hysteresis. Compared to the Norton model, the FDCFD model, which incorporates the effects of temperature and transient deformation, predicts larger displacements, volume shrinkage, and plastic zones, resulting in lower safety factors. For an operating pressure range of 13-17 MPa, the FDCFD model predicts a volume shrinkage of 9.51% and a maximum displacement of 2.44 m, while the Norton model predicts 5.36% and 1.55 m, respectively. This study provides valuable insights into the optimal design and operation of CAES plants in the Huai'an salt formation.