Analysis of the mechanical and leakage characteristics of surrounding rock in sandstone compressed air storage caverns after lining cracks

Abstract

Utilizing underground caverns for compressed air energy storage is one of the feasible methods for large-scale energy storage. Sandstone, being a relatively common stratum, offers significant flexibility in site selection when used to construct gas storage reservoirs. However, the cracking of the reservoir lining may lead to direct contact between the gas and the typically high-permeability sandstone, resulting in rapid gas leakage along the crack locations and adversely affecting the storage efficiency. Therefore, it is imperative to conduct preliminary experimental studies on the leakage characteristics and mechanical behavior of compressed air storage chambers within sandstone strata under specific operational environments.This study investigates the changes in the mechanical and permeability properties of sandstone after the reservoir lining cracks, under high-pressure alternating gas loads. Using the SAS-2000 multi-field coupling rock dynamic disturbance triaxial rheology experimental system and multi-scale high-temperature, high-pressure permeation monitoring system, the dynamic variations in porosity and permeability of sandstone under multi-stage alternating loads are explored. Additionally, the leakage rate of the gas storage reservoir post-cracking is evaluated.The experimental results indicate that under multi-stage alternating loads, the porosity and permeability of sandstone gradually decrease in the low-stress stage (0–30 MPa). With an increase in load levels, the development of micro-cracks leads to an inflection point in the changes in permeability, which then gradually recovers in the high-stress stage (>30 MPa). With an increasing number of cyclic loads, the compressive strength of sandstone gradually decreases, and hysteresis effects gradually emerge. The area of the hysteresis loop increases with both the stress level and the number of cycles, indicating a progressive increase in rock energy dissipation and damage accumulation.Furthermore, the study reveals that, under different crack ratios of 1 %, 2 %, 3 %, 4 %, and 5 %, the leakage volume increases as the crack range expands. The results show that when the crack ratio is between 1 % and 2 %, the daily leakage rate remains around 1 %, which is within an acceptable range. However, as the crack ratio increases further, the storage efficiency of the reservoir is significantly affected.