Simulation of Surface Uplift and Subsidence during Underground Hydrogen Storage (UHS) in a North Sea Depleted Hydrocarbon Field

Underground Hydrogen Storage (UHS) is expected to be an important technological component of the energy transition. UHS poses the risk of creating surface uplift or surface subsidence during fluid injection or withdrawal, and the resultant ground deformation may cause damage to surface facilities and infrastructure. In this paper, we conduct coupled hydromechanical modelling of the surface deformations caused by the injection of gaseous hydrogen into a depleted hydrocarbon reservoir. A field-scale, 4000 x 4000 x 3300 m model of a generic North Sea depleted gas field, including chalk overburden, shale caprock, sandstone reservoir, and shale underburden, is built, using rock properties and reservoir structure based on the Leman, Britannia, and Goldeneye gas fields. The Imperial College Geomechanics Toolkit (ICGT), a three-dimensional, linear-elastic, fully-coupled, hydromechanical simulator that can model fracture nucleation and growth, is employed to study ground elevation changes over a period of three years during the injection, storage, and withdrawal of gaseous hydrogen. The numerical implementation is validated against Geertsma's classical 'nucleus of strain' model for compaction during fluid depletion. The results show good agreement with the analytical solutions of Zimmerman (2018), Fjaer et al. (2008), and Mehrabian & Abousleiman (2015), for the reservoir pressure distribution, the reservoir expansion, and the surface uplift, respectively.