Abstract: The cross-sectional shape of an underground gas storage in a compressed air energy storage (CAES) power plant significantly influences its stress state, thereby affecting gas tightness and stability. It is conventionally considered that a circular cross-section yields the most favorable stress distribution. However, under anisotropic in-situ stress conditions, the hoop stress around a circular cavern is uneven and can induce localized lining cracking and gas leakage. To address this issue, this study investigates elliptical cross-section storage caverns using theoretical analysis based on elasticity theory. First, we propose a gas-tightness criterion based on the elastic stress state and derive an analytical solution for the elliptical cross-section’s optimal axial ratio. Second, we establish a stability criterion for lined rock caverns under anisotropic in-situ stress and develop a method to determine the operating pressure range for elliptical cross-sections, comparing it with the circular cross-section. Furthermore, we perform a parameter sensitivity analysis using FLAC3D to evaluate how factors affect the elliptical cross-section’s optimal axial ratio and operating pressure range. Finally, we establish an integrated calculation process to determine the optimal axial ratio and pressure range. Results show that, under anisotropic in-situ stress conditions, an elliptical cross-section designed with an optimal axial ratio can produce uniform hoop stress around the cavern. When an elliptical cross- section gas storage facility is designed with the optimal axis ratio, its pressure operating range is maximized. The lateral pressure coefficient, in-situ stress and internal pressure of gas storage are the main factors affecting the operating pressure range of elliptical section gas storage. These findings provide theoretical guidance for the shape optimization and pressure design of underground gas storage caverns.

Key words: compressed air energy storage, gas storage cavern, elliptical section, optimal axial ratio, operating pressure range