Modelling thermomechanical fracturing in underground hydrogen storage in salt caverns

In gas storage operations, intensive injection and withdrawal cycles can introduce structural failure due to thermally induced stresses, leading to the detachment of overhanging blocks from salt cavern walls. This study investigates the thermomechanical mechanisms governing block detachment in underground hydrogen storage using a joint enriched finite element method (JFEM) combined with cohesive zone modelling in DISROC software. An axisymmetric cavern geometry based on the Huntorf NK1 design is modelled, incorporating three overhanging blocks and both steady-state and transient creep components in the salt mechanical response. Comparative analysis of two salt types (fast-creeping Etrez and slow-creeping Asse) under identical thermomechanical loading reveals that rapid wall cooling during depressurisation (-13.8 bar/d) induces thermal contraction and tensile stresses exceeding rock salt tensile strength (1.5 MPa). Critical fracture initiation occurs at ∼15°C regardless of salt type, with block detachment sequences nearly identical between both salts (timing difference < 6 h). The results demonstrate that thermal stresses (1 MPa/°C cooling) dominate failure mechanisms over steady-state creep, while transient creep accelerates stress redistribution and damage localisation. These findings highlight that temperature control, rather than creep properties, governs cavern stability, emphasising the critical need for thermal monitoring and controlled depressurisation rates in underground hydrogen storage operations.