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Underground hydrogen storage in salt caverns is increasingly recognised as a critical component of future low-carbon energy systems, due to the low permeability and favourable mechanical properties of evaporite formations. However, evaporites commonly exhibit significant internal heterogeneity, including sulphate-bearing salts and siliciclastic interlayers, which may influence cavern stability, gas purity, and long-term operational performance. In particular, hydrogen-rock interactions may promote sulphate reduction and H2S generation, posing potential technical and safety risks.This study investigates the geological and geochemical controls on hydrogen storage in salt caverns, focusing on the Z2 cycle of the Zechstein Formation as a candidate for large-scale hydrogen storage. The approach integrates detailed geological characterisation, laboratory-based batch reaction experiments, petrophysical analysis, and geochemical modelling to assess both storage suitability and key uncertainties. Lithological variability, mineralogical composition, and geochemical reactivity are systematically evaluated, with particular emphasis on sulphate-rich intervals and siliciclastic interbeds.To address challenges associated with evaporite heterogeneity, the study develops a semi-automated workflow for wireline log analysis, enabling improved identification and characterisation of lithological variability in evaporite formations. Experimental and modelling results are used to constrain potential reaction pathways and assess their implications for cavern integrity and gas quality.By combining geological, experimental, and geochemical modelling approaches, this work provides new insights into hydrogen-rock salt interactions for both onshore and offshore Zechstein salt caverns. The results contribute to improved risk assessment, site selection, and operational strategies for underground hydrogen storage, supporting both scientific understanding and industrial deployment.