Hydrochemical Stability of Shale Caprocks During Underground Hydrogen Storage (UHS)

The global energy system is transitioning to low-carbon solutions, with an increasing proportion of renewable energy sources. The intermittency of renewable energy generation, e.g. from wind and solar power, however, leads to a rising demand for large-scale and seasonal energy storage. Hydrogen is regarded as a vital energy carrier, and underground hydrogen storage (UHS) in porous geological media is considered a promising option due to its substantial storage capacity, relatively low cost, and potential safety benefits. Nonetheless, hydrogen leakage through caprock formations and hydrogen–rock–brine interactions remain critical uncertainties that require further research.

This study aims to investigate the impact of hydrogen injection on the sealing integrity of shale caprocks. High-pressure, constant-temperature batch reactor tests are employed to simulate gas–brine–rock interactions under reservoir-relevant conditions. Shale samples with three distinct mineralogical compositions (carbonate-, pyrite-, and clay mineral-rich) are selected to represent different types of caprock lithologies. Experiments are conducted using various gas compositions, including hydrogen and potential cushion gases, to evaluate how mineralogical heterogeneity influences geochemical reactions and caprock performance.

The ongoing experiments aim to identify the most suitable (i.e. hydrochemically stable) caprock composition for underground hydrogen storage, as well as gas compositions that are more favorable as cushion gases to enhance storage safety. The results are expected to provide insights into caprock stability and sealing behavior during future hydrogen storage operations.