An experimental Investigation of hydrogen diffusion in heterogeneous Zechstein salt: Implication for cavern storage

Underground hydrogen storage in salt caverns is a promising strategy to balance large-scale renewable energy systems. However, the potential for hydrogen loss through heterogeneous salt formations remains poorly understood. This study presents an experimental assessment of hydrogen loss in salt core samples from the Zechstein Formation, in north-western Europe. Pressure decay experiments were performed at approximately 50 bar and 20 °C for 180 h under laboratory conditions. Mineralogical characterization using XRD, SEM/EDS, and thin sections revealed varying levels of impurities in the tested samples. It appeared that relatively pure halite samples exhibit minimal hydrogen loss, with cumulative losses of less than 0.0007 mol over the test period. In contrast, samples containing clay inclusions showed significantly higher hydrogen losses, reaching up to 0.0011 mol. Samples dominated by halite with anhydrite impurities demonstrated hydrogen losses as pure halite, suggesting a limited effect of the anhydrite on the diffusion behaviour. The experimental findings emphasize that clay-rich heterogeneities substantially enhance hydrogen loss, while halite purity maintains cavern integrity. These results provide essential experimental insights for evaluating the long-term security of hydrogen storage in Zechstein salt caverns. • The impact of impurities on the integrity of the salt cavern in heterogonies Zechstein formation was evaluated. • A systematic laboratory approach was developed to determine hydrogen diffusion into salt formations. • Hydrogen diffusion was evaluated through the pressure decay test at 50 bar and 20 °C. • Hydrogen loss of pure salt samples is generally negligible. • Salt samples with a high content of clays experienced greater hydrogen loss.