Initial Laboratory Measurements Probing Hydrogen Interactions with Eagle Ford Shale and Pyrite: Potential Implications for Subsurface Hydrogen Storage

Hydrogen (H2) has the potential to be a transformative technology as an enabler of a low-carbon future and a promoter of renewable energy. When H2 is injected and stored in the subsurface, it has the potential to interact with the caprock (usually shale), which overlies and seals the storage reservoir. This study examines the geochemical reactions or changes in surface morphology of Eagle Ford Shale, a proxy for caprock, upon exposure to H2 at 50 °C and 10.3 MPa. Exposures were also performed with N2 to provide an experimental control. Scanning electron microscopy with energy dispersive spectroscopy, atomic force microscopy, and optical photothermal-infrared spectroscopy were applied to quantify surface changes on the microscale and nanoscale level. Fluid chemistry changes were monitored by ion chromatography and inductively coupled plasma mass spectrometry. Exposure of Eagle Ford Shale to H2 gas alone did not result in any chemical alterations to the shale or any changes in the surface morphology. Exposure of Eagle Ford Shale to both H2 and water as well as N2 and water resulted in changes to the surface morphology because of gypsum dissolution and reprecipitation, thus indicating that H2 is not necessary to promote changes. Pure pyrite was the most reactive with H2 possibly resulting in a reduction to pyrrhotite. These initial studies suggest that the extent of reactions activated by hydrogen with caprock is minor under the temperature and pressure conditions that would represent underground hydrogen storage.