Hydrogen migration through natural rocks – an experimental approach

The investigation of hydrogen storage options in geological formations is an important part towards the development of technologies for the use of renewable energy. Promising storage capacities are expected in either rock salt deposits or porous sandstone formations with a gas-tight mudstone as cap rock. To obtain crucial data on hydrogen diffusion rates in these rocks, experimental studies are necessary as a first approach.

Here we present an experimental set up comprising two gas chambers, separated by the rock sample under investigation, where the driving force for gas migration through the rock sample is solely the chemical potential (concentration gradient). The hydrogen migration behaviour in samples of dry and wet sandstone, rock salt and mudstone was qualified by hydrogen break-through times and diffusion coefficients. Differences between the rock samples can be clearly seen. Also, the effect that wetted or water-saturated samples have higher retention due to closed pores and microcracks. The break through times varied from half an hour for dry sandstone to 918 hours for wetted rock salt. Based on concentration changes on the permeate side, hydrogen diffusion coefficients were derived in the range from 10^-9 to 10^-7 m²/s. The experimental set up proves to be suitable for determining diffusion parameters in natural rocks.