Hydrogen storage in depleted gas fields is a promising option for the large-scale storage of excess renewable energy. In the framework of the hydrogen storage assessment for the “Underground Sun Storage” project, we conduct a multi-step geochemical modelling approach to study fluid–rock interactions by means of equilibrium and kinetic batch simulations. With the equilibrium approach, we estimate the long-term consequences of hydrogen storage, whereas kinetic models are used to investigate the interactions between hydrogen and the formation on the time scales of typical storage cycles. The kinetic approach suggests that reactions of hydrogen with minerals become only relevant over timescales much longer than the considered storage cycles. The final kinetic model considers both mineral reactions and hydrogen dissolution to be kinetically controlled. Interactions among hydrogen and aqueous-phase components seem to be dominant within the storage-relevant time span. Additionally, sensitivity analyses of hydrogen dissolution kinetics, which we consider to be the controlling parameter of the overall reaction system, were performed. Reliable data on the kinetic rates of mineral dissolution and precipitation reactions, specifically in the presence of hydrogen, are scarce and often not representative of the studied conditions. These uncertainties in the kinetic rates for minerals such as pyrite and pyrrhotite were investigated and are discussed in the present work. The proposed geochemical workflow provides valuable insight into controlling mechanisms and risk evaluation of hydrogen storage projects and may serve as a guideline for future investigations.

Geochemical simulation models are the computational bottleneck for coupled reactive transport simulations. We investigate the use of a data-driven surrogate model in place of a geochemical simulation model to speed up the run-times of reactive transport simulations. This is a challenge because the surrogate model needs to use results of its predictions as inputs at each subsequent simulation step. We test the suitability of surrogate model approach on a popular reactive transport benchmark problem, often used for evaluating simulation models. We show that the concept is feasible and can make the simulations many times faster, however several open areas for future work remain

A high-pressure/high-temperature reactor has been used to lead PVT and H2-solubility experiments in saline solutions covering conditions for which no data are available in literature: salinity up to halite concentration, pressure up to 200bar and temperature up to 373K. The hereby presented preliminary results show significant deviations from theoretical models. Further analysis and more measurements are needed to assess precision and reproducibility of these measurements; however they pinpoint the importance of experimental work to reliably constrain predictive models