Hydrogen Exposure to Mt. Simon Reservoir Rock and Eau Claire Caprock: A Case Study within the Redfield Natural Gas Storage Field (Iowa, USA)

We assessed the reactivity with respect to hydrogen (H2) of the Mt. Simon reservoir rock and Eau Claire caprock to address the impacts of storing H2 as a mixture with natural gas or as pure H2 at the Redfield natural gas storage field (Iowa, USA). Rocks were exposed to H2 gas and NaCl brine under simulated subsurface storage conditions of 29 °C (302 K) and 8.3 MPa (1200 psig). Reactions were also performed with nitrogen (N2) gas to provide an experimental benchmark. Chemical or microstructural alterations were examined by scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM–EDS) before and after exposure to H2 and synthetic brine. Fluid chemistry changes were assessed with ion chromatography (IC). No chemical alterations or changes in the surface morphology were observed after 8 weeks of exposure to either H2 or N2 gas. Fluid chemistries after exposure were nearly identical for both H2 and N2 experiments, though small amounts of gypsum dissolution were indicated by slight increases in calcium and sulfate ions. This study suggests that the extent of reactions activated by H2 is insignificant under the studied temperature and pressure conditions for underground gas storage at Redfield. This suggests that this field may be favorable for H2 storage.