Subsurface hydrogen storage controlled by small-scale rock heterogeneities.

Subsurface porous rocks hold significant hydrogen (H 2) storage potential to support an H 2 -based energy future. Understanding H 2 flow and trapping in subsurface rocks is crucial to reliably evaluate their storage efficiency. In this work, we perform cyclic H 2 flow visualization experiments on a layered rock sample with varying pore and throat sizes. During drainage, H 2 follows a path consisting of large pores and throats, through a low permeability rock layer, substantially reducing H 2 storage capacity. Moreover, due to the rock heterogeneity and depending on the experimental flow strategy, imbibition unexpectedly results in higher H 2 saturation compared to drainage. These results emphasize that small-scale rock heterogeneity, which is often unaccounted for in reservoir-scale models, plays a vital role in H 2 displacement and trapping in subsurface porous media, with implications for efficient storage strategies. [Display omitted] • Pore-scale heterogeneity impacts H 2 flow and trapping in sandstones. • Flow direction has a pronounced effect on H 2 trapping in heterogeneous rocks. • Understanding small-scale rock heterogeneity is crucial to build reservoir models. [ABSTRACT FROM AUTHOR]