Salt rock exposure to hydrogen: evolution of mineralogical, pore-system, and elastic properties

As global decarbonization efforts accelerate, hydrogen (H2) is emerging as a key energy carrier in the transition toward a low-carbon economy. Storing surplus energy is essential to mitigate the intermittency of renewable sources, and underground hydrogen storage (UHS) has therefore attracted growing interest as a cost-effective and scalable solution.This study investigates the evolution of mineralogical, pore system, and elastic properties (Young’s modulus and Poisson’s ratio) of salt rocks from deep evaporitic deposits in the Ebro Basin (Spain), exposed to hydrogen in an autoclave under controlled batch conditions (4.5 MPa, 30 ºC, 1 cycle of 30 days). Samples were characterized before and after exposure using optical microscopy (OpM), digital image analysis (DIA), scanning electron microscopy (SEM), and P- and S- wave velocity measurements. The combined use of these techniques provides a comprehensive approach to assess the effects of hydrogen on rock properties.The samples are predominantly composed of white-grey halite (NaCl), with minor impurities of celestine (SrSO4), anhydrite (CaSO4), sylvite (KCl), and silicates. Following hydrogen exposure, the samples were re-evaluated to examine potential microstructural and physical modifications, as well as the behaviour of the impurity phases under the imposed experimental conditions. These preliminary findings provide a basis for discussing hydrogen-rock interactions in evaporitic formations and their relevance for assessing salt deposits as potential reservoirs for underground hydrogen storage (UHS)The research was conducted within the Project PIEMAX-GEO4TREE and the Format-GEO collaboration network (Ref. LINCGLOBAL 25008).