Effect of hydrogen on calcite reactivity in sandstone reservoirs: Experimental results compared to geochemical modeling predictions

Abstract

Geologic reservoirs including calcite bearing sandstones are among the highest potential structures that can serve as sites for underground hydrogen storage (UHS). However, to confirm the viability of sandstone reservoirs, better knowledge about rock–porewater–hydrogen gas (H2) systems is needed. Previous geochemical modeling studies predicted significant H2 loss induced by the reaction of carbonate minerals with H2. Our recent combined experimental-modeling study investigated the geochemical impact of H2 on calcite (CaCO3), a characteristic rock forming mineral in potential hydrogen storage reservoirs. Static batch reactor experiments were conducted in the pressure and temperature range (100 bar, 105 °C) of UHS to track the effect of H2 on calcite. The experiments demonstrated the non-reactive behavior of calcite as there were no signs (chemical and morphological) of increased calcite dissolution in H2 atmosphere compared to results with inert gas (N2). On the contrary, the kinetic PHREEQC model, using a non-modified thermodynamic database, predicts intensive reactions between calcite and H2, resulting in extensive calcite dissolution and methane formation. Our conclusion, therefore, is that the thermodynamic databases of geochemical modeling must be reviewed for UHS and modified for such projects to provide reliable results. This study gives practical insight into the potential path forward to correct this problem.