Investigation of thermal-mechanical effects on salt cavern during cycling loading

Highlights: • A coupled thermo-mechanical model is established for stability analysis of cavern wall. • The thermal-mechanical effect on salt cavern during cycling loading is investigated by thermal-mechanical coupling model. • The thermal damage on salt cavern roof occurs after the most severe gas withdrawal period. • The retain time of low pressure operation after gas withdrawal aggravates the thermal damage, resulting in collapse. Traditional stability analysis for salt cavern as UGS overlooks the thermal effects induced by cycling loading and cannot predict the potential risk. In this study viscoelastic WIPP model is employed to describe the temperature-dependent creep behavior of rock salt. A thermal-mechanical simulation framework is established to couple the effect of mechanical stress and thermal stress. A coupling thermal-mechanical numerical model implemented by FLAC3D in combination with the WIPP creep model is proposed. A field case, Cavern L, in Jintan, Jiangsu Province of China is demonstrated in this paper to explore the thermal response to gas injection-and-withdrawal process. The results show that there is tensile stress concentration region at the cavern roof. The dynamic process of thermal damage evolution and block falls on cavern roof is also investigated. The disintegration of rock salt mass at cavern roof occurs after the most severe gas depressurization period, and the retain of low pressure after gas withdrawal aggravate the thermal damage. It indicates that the thermal-induced tensile stresses are critical for salt cavern stability assessment. The feasibility and accuracy of the proposed thermal-mechanical modeling is verified by the field case, and the simulation results of thermal damage are coincided with the sonar results. This analysis confirmed the influence of thermal-mechanical effects on salt cavern wall. The approach used in this study provides an improved method for the stability evaluation and optimal operation parameters for salt caverns.