Long-term cyclic thermo-mechanical behavior of vertical and horizontal salt caverns for hydrogen storage

Underground salt caverns are considered viable options for hydrogen storage owing to their favorable geological properties and large storage capacity. However, during underground hydrogen storage operations, the circumference of the salt cavern is subjected to cyclic thermo–mechanical loading caused by an related pressure fluctuations. The associated long-term thermo-mechanical processes can negatively impact the cavern capacity and stability. This paper presents a numerical analysis to enhance our understanding of the long-term behavior of salt caverns under coupled thermo-mechanical cyclic loading resulting from hydrogen storage operations. To accomplish this, the relevant thermo-mechanical in-situ conditions and key stability and usability indices of the salt cavern are initially presented. A thermo-mechanical-coupled constitutive model that integrates elasticity with temperature-dependent creep and plasticity is then used to simulate the behavior of rock salt during cavern operation. Subsequently, large three-dimensional models of salt caverns were created to simulate thermal and mechanical processes, including time-dependent deformation and temperature evolution for horizontal and vertical salt cavern’s orientations over 60 years of hydrogen storage. The numerical results indicate that the deformation behavior differs at the top, sides, and bottom of vertical and horizontal salt caverns, with each region exhibiting distinct deformation patterns. Moreover, when the internal temperature and pressure of the cavern exceed permissible limits, localized tensile and shear failures may develop along the cavern walls, posing potential risks to structural integrity. A parametric study considering variations in operational conditions further revealed that increasing stress within safe limits reduces displacement around the cavern wall and improves capacity. In addition, temperature variation was found to influence capacity. These findings demonstrate the critical role of cavern orientation and the long-term TM-coupled behavior of salt caverns in ensuring optimal design and long-term stability.