Hydrogen corrosion mechanism and multi-field coupled constitutive model for wellbore cement sheath in salt cavern hydrogen storage

Salt cavern hydrogen storage is a key technology to meet the demand for large-scale hydrogen energy storage. The long-term performance evolution of the wellbore cement sheath in a simulated salt cavern hydrogen storage conditions (55°C, 20 MPa) is directly related to the safety and sealing integrity of the storage. In this study, accelerated corrosion tests lasting 0–30 days were conducted on Class G oil well cement under simulated salt cavern hydrogen storage conditions. The uniaxial/triaxial mechanical properties and gas permeability of the completion cement before and after corrosion were systematically measured, and the microstructural evolution was revealed by XRD and SEM. The results show that hydrogen corrosion has a dual effect: local dissolution and weakening of the gel matrix, and pore filling caused by re-precipitation of dissolved ions. The macroscopic performance exhibits a competition mechanism regulated by confining pressure. Under low confining pressure, the strength decreases leading to increased brittleness, with damage being dominant. Under high confining pressure, the strength increases leading to improved ductility, with filling enhancement being dominant. Based on these findings, an elastoplastic constitutive model coupling chemical damage and plastic deformation, along with a permeability evolution equation, was constructed. Engineering-scale numerical simulations were realized through secondary development of ANSYS UPFs. The results indicate that the cement sheath after hydrogen corrosion is less susceptible to damage under cyclic loading and can maintain higher integrity during multiple injection-production cycles. This study provides a scientific basis for the wellbore integrity assessment of salt cavern hydrogen storage facilities.