Pore-scale 3D imaging of hydrogen storage in rocks

Abstract

Escalating concerns over climate change have accelerated the need to transition towards cleaner energy sources, such as hydrogen. For a sustainable hydrogen economy, effective storage solutions are important. Subsurface porous rocks offer a promising solution, capable of storing substantial volumes of hydrogen for varying durations to meet fluctuations in energy demand. However, a comprehensive understanding of hydrogen flow and entrapment within these rocks, particularly under reservoir conditions, remains a significant challenge. In this thesis, X-ray micro-tomography is used to investigate the pore-scale distribution, trapping, and recovery of hydrogen under subsurface conditions. Through 3D flow-visualisation experiments on sandstone rocks, initial and residual hydrogen saturations are quantified, providing an assessment of the hydrogen storage capacity and recovery efficiency of these rocks. Additionally, the potential dissolution of hydrogen in brine is observed, a phenomenon that could contribute to hydrogen loss during storage and production. Furthermore, the influence of small-scale rock heterogeneity is investigated through experiments on a layered rock. These experiments highlight how subtle rock structure variations impact hydrogen displacement, leading to reduced storage capacity upon injection and significant hydrogen trapping during production. Such findings stress the pivotal roles of pore-scale processes and small-scale rock heterogeneity in the design, selection, and implementation of subsurface hydrogen storage systems. Moreover, a comparison of experimental results with a pore-network model reveals that simplistic models fall short in accurately predicting hydrogen flow and trapping in real rocks, particularly heterogeneous media. This highlights the importance of experimental research, such as this study, in advancing our understanding and optimisation of subsurface hydrogen storage.