Damage Evolution of Sandstone Under Cyclic Loading for Underground Gas Storage

ABSTRACT: Underground gas storage plays an important component of emergency gas supply and peak shaving capabilities in winter. It plays a vital role in ensuring the security of natural gas supply. Pressure variations and frequency changes in gas storage can easily cause fatigue damage to formation rocks. The M reservoir is currently in the initial phases of development, and conducting a thorough analysis of reservoir damage deformation under various storage conditions, including storage frequency and fluid pressure fluctuations, is crucial for ensuring safe and efficient operation. In this study, uniaxial compression tests and cyclic loading mechanical experiments are conducted on sandstone samples from M gas storage in Junggar Basin. These experiments combined with the operational data of M gas storage investigate the influence of different frequencies and amplitudes by stress-strain curves and hysteresis loop. Damage variables D are introduced to quantitatively analyze the damage behavior of sandstone at different frequencies and amplitudes. The results show that the compressive strength of sandstone is affected by amplitude and frequency. On the one hand, the higher the amplitude, the lower the rock strength, the fuller the hysteretic loop. On the other hand, the lower the frequency, the lower the rock strength. From the point of view of damage variable, the increase of amplitude prolongs the development cycle of inelastic strain. The higher the amplitude, the greater the final damage. When the amplitude is constant, the increase in frequency reduces the interaction time between the stone particles and the degree of rock damage decreases. The study provides a reference for the construction and safe operation of gas storage reservoirs. 1. INTRODUCTION Underground gas storage is an important infrastructure for the storage of natural gas resources and the peaking of natural gas supply and demand(He,A., Ma,Q., Pang,Y. et al., 2023). Around the world, there are four main types of gas reservoirs: porous reservoirs, salt caverns, caverns, and depleted reservoirs. Depleted reservoir type gas storage is the most dominant type, with over 80% of the total volume ratio dedicated to working gas. By 2023, China had built 28 gas storage reservoirs with a peaking capacity of 165×109 m3. However, their working capacity only represents 4.4% of China's natural gas consumption, which is far below the minimum requirement of 12% set by the International Gas Union(Changyin, D, Chen, C, Lizhi, W, 2022). Thus, the conversion of depleted gas reservoirs into gas storage has been identified as a highly promising tool. The attention of academic institutions, governments, and oil companies has been drawn to accelerating the construction of gas storage.