Fluid-Fluid and Rock-Fluid Parametric Investigation of The Underground Storage of Hydrogen in a Deep North Sea Aquifer

Hydrogen is a clean energy form aiding in achieving the significant net zero targets while fulfilling objectives of reducing carbon emissions by major economies, thus transitioning from fossil fuel to sustainable energy centres. To mitigate the high demand for electricity and heat in the peak winter season in Europe, it is proposed to store the excess electricity-converted-hydrogen in saline aquifers, salt caverns, and depleted oil and gas reservoirs. These geoformations can store GigaWatt scale hydrogen energy, significantly larger than the other storage means. In this work, we investigate the impact of aquifer-related mechanisms and parameters on the performance of underground hydrogen storage in a North Sea aquifer utilizing the numerical simulation approach. The effect of heterogeneity in permeability, relative permeability hysteresis, fluid-fluid solubility of hydrogen in formation brine and the diffusion over the predictive simulation periods were investigated in this study. Hydrogen gas injectivity and recovery efficiency were observed to be significantly influenced by the aquifer’s permeability heterogeneity. Moreover, the relative permeability hysteresis further decreased the hydrogen gas injectivity and recovery, which occurs due to the trapping of the residual hydrogen gas in the trailing edge of the migrating hydrogen plume inside the aquifer. This is more clearly visible during the hydrogen production cycles. The inclusion of hydrogen solubility and hydrogen diffusion indicated negligible effects when evaluated independently. However, their combined evaluation with the above factors, has shown an impact on the performance of underground hydrogen storage in term of lower recovery efficiency. Investigation of the addition of CO₂ as a cushion gas is projected to yield hydrogen gas recovery while sequestering and storing the large volumes of CO₂ achieving the noticeable decarbonisation targets.