Sensitivity analysis of controls on regional pressure propagation during large-scale carbon storage in the Bunter Sandstone Formation, Silverpit Basin (Southern North Sea, UK)

Large-scale deployment of CCS operations in regionally extensive saline aquifers requires robust assessment of pressure propagation, boundary connectivity and plume behaviour beyond individual storage sites. This study presents a regional-scale sensitivity analysis of CO 2 injection into the Bunter Sandstone Formation of the Silverpit Basin (Southern North Sea, UK), integrating structural uncertainty, petrophysical heterogeneity, boundary transmissibility and aquifer connectivity within a unified dynamic modelling framework. Fourteen scenarios were simulated using a calibrated geocellular model to evaluate the response to injection of 1 Mt/yr/well over 50 years across 14 wells, followed by 5000 years of post-injection observation. Additional scenarios tested alternative depth-conversion models, heterogeneous variogram ranges, confined and semi-open boundary conditions, enlarged connected aquifer volumes, overpressured initial conditions, and a tripled injection rate strategy. Results indicate that approximately 700 Mt of CO 2 can be injected under hydrostatic conditions while maintaining bottom-hole pressure constraints, whereas overpressured and intensified injection scenarios significantly reduce injectivity. Plume migration remains largely confined within four-way dip closures, with heterogeneity influencing plume anisotropy but not containment. In contrast, pressure propagation extends tens of kilometres beyond the plume footprint and is highly sensitive to boundary conditions. Transmissible boundaries, including a seabed outcrop, promote continuous long-term pressure dissipation and brine displacement outside and within the aquifer. All scenarios exhibit at least one inter-regional brine flow reversal, demonstrating that injection-induced regional pressure gradients can modify hydrogeological flow between storage licences. The results identify aquifer connectivity as the dominant control on regional pressure behaviour, with implications for post-operation estimates and licence-scale interference in this region.