Geomechanical modelling of subsurface storage of hydrogen in depleted natural gas reservoirs

Underground Hydrogen Storage (UHS) in depleted gas fields is a novel energy transition technology that is the most efficient solution for satisfying periods of renewable energy deficit in low carbon energy economies. The cyclical injection, storage and withdrawal of an ultra-low density, ultra-low viscosity fluid such as hydrogen may exacerbate geomechanical phenomena that compromise the integrity of the storage, damage surface equipment and infrastructure, risk the loss of a social license to operate, invoke large economic losses due to loss of stored product, and in the worst case scenario, lead to the loss of human life. In this work, key geomechanical phenomena including induced seismicity, caprock integrity, and surface uplift and subsidence, are examined during the multi-year storage of gaseous hydrogen into various versions of a generalised North sea depleted gas field model. Three-dimensional, linear elastic, monolithically-coupled, hydromechanical, finite element simulations are performed using the Imperial College Geomechanics Toolkit (ICGT) to evaluate these phenomena. A comprehensive literature review of rock mechanical and lithological properties was performed to design the model. Processes such as fault slip, fracture growth, damage, fracture nucleation and poroelastic rock expansion and compaction are considered. The ICGT is validated against a published numerical CO2 storage study, and the classical analytical solutions of Geertsma, to enhance confidence in the fault slip and uplift/subsidence computations herein, respectively.