Geomechanics of hydrogen storage in a depleted gas field.

We perform a simulation study of hydrogen injection in a depleted gas reservoir, to assess the geomechanical impact of hydrogen storage, relative to other commonly injected gases (methane, CO 2). A key finding is that the differences in hydrogen density, compressibility, viscosity and thermal properties, compared to the other gases, result in significantly less thermal perturbation at reservoir level. The risks of fault reactivation and wellbore fractures due to thermally-induced stress changes are significantly lower when storing hydrogen compared to results observed in CO 2 scenarios. This implies that hydrogen injection and production has a much smaller geomechanical footprint, with benefits for operational safety. We also find that use of nitrogen cushion gas ensures efficient deliverability and phase separation in the reservoir. However, in this study, a large fraction of cushion gas was back-produced in each cycle, demonstrating the need for further studies of the surface processing requirements and economic implications. [Display omitted] • Geomechanical modelling assesses the risks associated with hydrogen storage. • Diffusivity, dissolution and methanogenesis have negligible effect on models. • Thermal perturbations associated with storage alter fracture pressures. • Significant mixing of hydrogen with cushion gas is observed. • Hydrogen storage presents less geomechanical risk than CO 2 or methane storage. [ABSTRACT FROM AUTHOR]