Geochemical reactivity of hydrogen with sandstone reservoir rocks: feasibility of underground porous storage

Underground hydrogen storage in porous rocks presents a promising solution for renewable energy storage. While geochemical reactions between hydrogen and reservoir minerals are generally believed to have minimal impact on hydrogen loss or reservoir integrity, this assumption is based on limited experimental evidence. To accurately assess hydrogen's role in geochemical interactions, it is essential to conduct comprehensive batch experiments with appropriate control scenarios that distinguish hydrogen-induced effects from those arising solely from fluid–rock interactions. This study investigates the geochemical reactivity of hydrogen with reservoir sandstones containing less than 2% pyrite. Batch experiments were conducted using cylindrical core samples under conditions of 100 °C and 100 bar hydrogen partial pressure for five weeks. Three scenarios were examined: (1) dry samples exposed to hydrogen, (2) synthetic saline fluid-saturated samples with hydrogen, and (3) synthetic saline fluid-saturated samples with helium (as a control). Pre- and post-experimental analyses included measurements of permeability, porosity, magnetic susceptibility, thin-sections, fluid elemental concentrations (via ICP-OES and IC), and gas composition. In contrast to our previously studied pyrite-free Buntsandstein reservoir sandstones, the results from this study provide evidence that pyrite is reactive with hydrogen, potentially influencing other reservoir parameters. Specifically, samples exposed to hydrogen showed more than a twofold increase in magnetic susceptibility compared to those in the helium control group, indicating a potential formation of pyrrhotite from pyrite. Ongoing research into pyrite-bearing rocks aims to enhance the generalizability of these findings and contribute to more robust risk assessments for underground hydrogen storage.