Geological storage of hydrogen: natural analogues, flow cell experiments and mass transport modelling
McMahon, Christopher, J.
Decarbonising the global energy mix is crucial to lowering greenhouse gas emissions and combating climate change. The introduction of renewable (low carbon) energy sources and the removal of fossil fuel energy sources creates uncertainty in energy supply and energy security, particularly across seasonal timescales. Many types of energy storage schemes could store large amounts (up to TW) of excess energy for use when demand is high (e.g. Pumped Hydropower, Batteries), however only the geological storage of hydrogen has the capability to sustain energy demand over seasonal timescales, while also decarbonising multiple energy sectors (e.g. heat, transport, power and industry). Currently, to sustain hydrogen production at large scale requires the use of fossil fuels (steam methane reformation, SMR) and to be low carbon, requires carbon capture, utilisation and storage (CCUS). This research explores the potential of coupling hydrogen production from SMR with CCUS, using the produced CO₂ as the cushion gas for the hydrogen storage reservoir. State of the art 1D hydrogen flow experiments coupled with analytical and numerical models are used to characterise how hydrogen and CO₂ mixtures behave in porous media. The results show that the type of cushion gas influences the speed which hydrogen flows through porous rock and that the key mass transport processes in operation are dispersion and matrix diffusion. The results highlight the need for better characterisation of hydrogen properties to understand how hydrogen would behave under subsurface storage conditions. The large-scale deployment of hydrogen as a low carbon energy vector will require further in-situ pilot projects to demonstrate a safety case, appropriate site suitability assessments, supportive policy frameworks and crucially a positive public image.