Temperature dependence of hydrogen diffusion in reservoir rocks: implications for hydrogen geologic storage†

Abstract

Hydrogen (H₂) has recently gained momentum as a promising clean energy alternative to fossil fuels. The intermittent nature of renewable energy, as the source of green H₂, necessitates temporary H₂ storage in subsurface geologic formations. To quantify storage potential and leakage risk, it is crucial to fully characterize subsurface H₂ transport behavior. This work aims to measure the diffusion of H₂ through relevant reservoir rocks, including two sandstones (Amherst Grey and Birmingham) and a limestone (Indiana). Breakthrough as a function of temperature is measured and used to calculate the effective diffusion coefficients and activation energy for diffusion at three different temperatures between 20 and 75 °C. Calculated diffusion coefficients are then used to estimate the subsurface plume size during storage in sandstone and limestone reservoirs. We observe that diffusive flow slightly expands plume size by up to 7%, and this effect is most pronounced in formations with low water saturation. While the use of cushion gas can maintain reservoir pressure and enhance injection efficiency, it can also enlarge H₂ plume and hinder the recovery process due to molecular diffusion if the cushion gas differs from H₂.