Injection strategy development for CO2 storage in a multi-trap storage site considering hydrodynamic and geomechanical restrictions

Geological storage of CO₂ contributes to mitigating climate change, but successful storage depends on many subsurface hydrodynamic and geomechanical factors. This study outlines the development of a CO₂ injection strategy for a potential multi-trap storage site in the German North Sea by jointly honouring the geomechanics as well as hydrodynamic and geological constraints. The site comprises three structural closures, each covering an area of tens of km². Based on site-specific geology and petrophysical data, static storage capacities of the individual closures as well as the closure combinations are estimated. Each closure has a distinct configuration and drainage area, resulting in different CO₂ phase dynamics in the subsurface, due to a different interplay of gravity, capillary and viscous forces. A 3D reservoir model is developed and used to simulate CO₂ injection with a rate of 10 Mt/a over 30 years, followed by a 100-year post-injection phase, while accounting for the regional hydraulic boundaries. The allowable pressure limit is derived using dedicated geomechanical simulations. The individual settings of each closure result in varying depths and injectivities, which lead to different numbers of injection wells and their placement due to well interaction. Furthermore, pressure accumulation occurs depending on the relative position of the closure to the hydraulic boundaries, reducing achievable capacity. Consequently, injection well planning and optimisation efforts should prioritise settings that demonstrate high injectivity, high achievable storage capacity and a high allowable pressure window.