Geological Storage of Hydrogen: Learning from natural analogues

The potential role of hydrogen in achieving a net zero emissions future is gaining traction. A hydrogen economy would likely be supported by geological formations in which to store hydrogen at times of excess and to extract in times of demand, akin to subsurface natural gas storage.

Minimising the risk of hydrogen leakage is not only important to support the safety case for geological storage, but also to constrain risk of any economic losses from the migration of hydrogen from its intended storage formation. As such, deepening scientific understanding of the processes governing hydrogen containment and leakage is fundamental for: (a) prospecting of natural hydrogen plays, (b) informing effective site selection for geological hydrogen storage, and (c) the design and performance requirements of appropriate monitoring of these sites.

Several earth processes generate hydrogen, and naturally occurring subsurface hydrogen accumulations and hydrogen seeps (where hydrogen is seeping to surface) present opportunity for study to further knowledge on geological containment of hydrogen. Here, we present a synthesis of the available literature on natural analogues for hydrogen storage and seepage around the world to elicit the factors governing containment/leakage and seep characteristics. We also consider how learnings from other subsurface energy sectors such as geological CO₂ storage might be translated and applied to hydrogen storage.

We find that currently there are few natural analogues for hydrogen – there are only eight hydrogen seeps and fewer hydrogen accumulations documented in the scientific literature (though we postulate that other sites of hydrogen accumulation and seepage may exist but are yet to be documented). For all known analogues, the hydrogen is thought to derive from deep seated processes (e.g. serpentenization) rather than superficial bacteriological or other processes. Hydrogen seepage can occur in clusters or in isolation, and the location, distribution and morphology of seeps are controlled by geological factors such as regional stress, occurrence of faults, and properties of the host rock. These factors are similar to those governing CO₂ seepage, but we note differences, too. One documented hydrogen accumulation is shallow (80-150m). Hydrogen and methane occur in different proportions at different depths in the reservoir complex. This implies that different rock properties constitute a seal/reservoir for methane and hydrogen. The parameters that define a hydrogen “play” may therefore be different to a hydrocarbon play.

Overall very little is known about how hydrogen migrates and is trapped in the subsurface, and there are few studies of natural analogues. Our work highlights the need for further research around the factors that govern hydrogen fluid flow, and thus the degree to which knowledge of fluid flow of other geofluids can be translated and applied to ensure effective and secure geological hydrogen storage.