Investigation of the effects of hydrogen injection and withdrawal frequency on stability and tightness of the salt cavern based on a novel coupled thermal-hydro-mechanical model

Using salt caverns for the Underground Hydrogen Storage (UHS) is a promising means to address climate change and the energy crisis. However, the complex Thermal-Hydro-Mechanical (THM) coupling problems existing in the UHS salt caverns pose a challenge to the safe and efficient storage of hydrogen. In this paper, a coupled THM model which considers the thermodynamic properties of hydrogen, the thermal expansion and creep of the surrounding rock, and the hydrogen seepage was proposed. The model was validated by the results of a field test and a numerical simulation. A numerical model was established to analyze the stability and tightness of the UHS cavern in bedded salt rock under different Frequencies of Hydrogen Injection and Withdrawal (FHIW). The results show that with the increase of the FHIW, there is an increase in the variation ranges of pressure and temperature. The distributions of the von Mises stress, the first principal stress and the effective creep strain suggest that the risk of failure induced by creep and tensile is more significant at the interface of the salt rock and interlayer on the cavern wall. Additionally, the displacements, Volume Loss Rate (VLR), and hydrogen loss ratio of the cavern all increase with the increase of FHIW, and the maximum displacement of the cavern is found at the roof. The interlayer is the main channel for hydrogen leakage, and the existence of the "seepage step" and "seepage peak" indicates that frequent injections and withdrawals primarily impacts the region close to the cavern.