Understanding Underground Hydrogen Storage Across Scales

Abstract

To enable the energy transition, renewable energy sources such as wind and solar are playing an increasingly central role. However, their weather-dependent nature makes balancing energy supply and demand challenging. While short-term fluctuations can often be managed with batteries or other local storage solutions, many countries, such as the Netherlands, are expected to face large seasonal energy imbalances of several tens of terawatt-hours (TWh), far beyond the capabilities of conventional technologies such as batteries.

Underground Hydrogen Storage (UHS) has therefore emerged as a promising solution. Storing hydrogen in geological formations such as depleted gas reservoirs or aquifers at depths of several kilometers can provide storage capacities on the order of several terawatthours. These reservoirs are porous rocks of solid grains and interconnected voids, where hydrogen is stored in the pore space. This introduces complex flow dynamics and technical challenges across multiple scales: from the molecular interactions of hydrogen with other fluids present in the reservoir, to the flow through micrometer-scale pore channels, up to reservoir-scale processes spanning several kilometers.

This thesis advances the understanding of UHS by addressing knowledge gaps across multiple scales, combining molecular simulations, microfluidic experiments, pore-scale modeling, and the development of a site selection framework. At the molecular scale, missing datasets of thermophysical properties of hydrogen–brine systems were obtained by using molecular simulations. These properties, including densities, viscosities, interfacial tensions, solubilities, and diffusivities, are essential for accurate large-scale reservoir simulations.

At the pore scale, microfluidic experiments were conducted to measure dynamic contact angles in glass micromodels that mimic the micrometer-scale channels of porous rocks. These measurements reveal how wettability depends on pore geometry and governs flow dynamics. Complementary pore-scale simulations using the lattice Boltzmann method were performed to explore mechanisms of hydrogen trapping and bypassing under varying flow rates, pore shapes, and capillary conditions. Together, these results improve our understanding of multiphase flow processes critical for predicting and maximizing hydrogen flow behaviour and recovery efficiency.

At the reservoir scale, a systematic site selection framework was developed for identifying suitable depleted gas fields for UHS. This framework integrates multidisciplinary criteria including reservoir performance, geomechanical stability, bio-geochemistry, and techno-economic feasibility providing a practically accessible and reliable method for screening and ranking potential storage sites.

By linking insights across scales and disciplines, this thesis strengthens the scientific foundation for the safe, efficient, and reliable deployment of UHS. The findings contribute critical data, improve predictions, and support decision-making toward enabling large-scale UHS.