Designing Geometrically Stable Salt Caverns for Underground Hydrogen Storage: A Case Study from Northeast England

Underground hydrogen storage (UHS) in salt caverns is essential for enabling seasonal energy balance and enhancing the resilience of future hydrogen-based energy systems. The long-term mechanical stability of such caverns is highly dependent on their geometry and the viscoplastic behavior of the host salt rock. This study presents a comprehensive geomechanical assessment of multiple cavern geometries within the Boulby Halite Formation in Northeast England, a region of increasing strategic relevance for hydrogen infrastructure deployment. Using a three-dimensional finite difference approach, the stability of spherical, bell-shaped, inverted bell-shaped, droplet-shaped, undulating-walled, ellipsoidal, and cylindrical caverns with varying aspect ratios was evaluated under realistic cyclic hydrogen injection and withdrawal scenarios over a 30 year operational period. Results demonstrate that the cavern geometry critically governs stress redistribution, deformation, and operational viability. Symmetrical or tapered configurations with broader bases, particularly spherical, droplet-shaped, and bell-shaped caverns, exhibited the most favorable performance, consistently maintaining strength-to-stress ratios above 1.0, effective strains below 0.1%, and volume shrinkage under 8%. In contrast, geometries with sharp curvature changes or enlarged caps showed stress amplification on the roof and floor, increasing the instability. Moreover, elongated profiles with high diameter-to-height ratios (d/h) in cylindrical and ellipsoidal caverns led to localized overstress, nonuniform strain, and up to 10.7% volume loss. Overall, the findings provide quantitative design insights for safe, long-term UHS in bedded halite formations, supporting robust hydrogen grid integration in Northeast England and similar geological settings.