## 4 Experimental Studies at Laboratory Scale
### Case Studies of Experimental Research
[110] conclusively demonstrates that there is no risk of hydrogen loss or reservoir integrity degradation due to abiotic geochemical reactions in sandstone reservoirs. According to [PERSON] et al. [63] and [PERSON] et al. [139], the interaction between hydrogen and highly saline formation fluids is known to enhance hydrogen solubility, which, in conjunction with the acidification of the formation fluid, can result in the partial or complete dissolution of the carbonate and anhydrite cements. These results highlight the critical role of mineralogical composition, particularly cementing materials, in determining the reactivity of rocks towards hydrogen in geological storage contexts. The presence of carbonate and anhydrite cements in detrital rocks, combined with specific reservoir conditions, significantly impacts the nature and degree of hydrogen-rock interactions. However, in some case studies [141], the fluid/H\({}_{2}\) interface with a clay-rich sandstone indicates minimal alteration in porosity and mineral content. In the context of temporary geological H\({}_{2}\) storage, the inertness of salt towards hydrogen and its substantial imperviousness are of utmost importance [60]. Nonetheless, according to [PERSON] et al. [142], laboratory investigations have identified several mechanisms by which hydrogen might be lost during its storage in salt caverns. These mechanisms are generally categorized into chemical and physical processes based on how they affect the state of hydrogen from a chemical perspective through mineral reactions and microbiological reactions. That is, CO\({}_{2}\) can be generated, which, in addition to compromising the purity of the stored hydrogen, poses a corrosive threat to the well casing, jeopardizing the structural soundness of the storage system [90]. Also, microbial activity feeds on hydrogen, using this gas as an energy source in their metabolic processes and exhaling methane and hydrogen sulphide as by-products [143]. From the physical point of view, the losses are through leakage loss, dissolution loss, and adsorption loss. In the context of the geomechanical evolution of samples exposed to H\({}_{2}\), in case studies [60], it is found that parameters such as material deformation, viscoplasticity, microcracking, and crack closure itself behave adequately to ensure the impermeability of the rock. According to [PERSON] et al. [144], the experiments and models indicate that, in general terms, the temperature can vary significantly during hydrogen storage and influence the pressure inside the cavern. Furthermore, the largest temperature amplitudes occur in shorter cycles. This implies that laboratory tests should emulate these behaviors in order to better adjust to the real behavior in the reservoir and thus, be able to provide information that contributes to a better understanding of the rock/gas/brine interaction. In general, laboratory tests are designed to characterize the properties of rocks and fluids, as well as their integration through the study of specific parameters. These tests aim to determine the chemical, biological, and mechanical interactions within the rock/gas/fluid system [32]. The compiled studies seek to expand knowledge on this topic and contribute to the industrial development of underground hydrogen storage (UHS).