A conceptual CO2 fill-and-spill mega-fairway in the UK Southern North Sea: A new approach to identify and optimise large-scale underground carbon storage (CCS)

This work explores the subsurface CO2 storage potential in UKCS Quadrants 43–44, by integrating 3D seismic interpretation, regional wellbore data and CO2 migration modelling. We show 11 Bunter Sandstone domes linked together in a fill-and-spill “Bunter Mega-Fairway”. These traps host a theoretical storage capacity of 8.4 Gt CO2 (≈3–4 times the filled-to-spill theoretical capacity of the proposed Endurance storage site), while lessening CO2 leakage risks. Within the mega-fairway, the Triassic Bunter Sandstone reservoir shows a P10-P90 thickness of 78–219 m, along with moderate-high porosities (11–28 %) and permeabilities (9–669 mD). A regionally-connected reservoir is suggested from spatially consistent, near-hydrostatic aquifer pressure gradients (≈0.51 psi/ft). The top-seal is laterally effective and structural closures are lower than the CO2 columns necessary to breach the seal. At the mega-fairway storage depths, CO2 would inhabit the reservoir as a supercritical fluid, enabling it to naturally migrate buoyantly from one trap to another, away from strategically-placed injector sites. Through the integration of migration spill-point modelling, multi-physics seabed monitoring nodes and fill-and-spill injection management, the maximum storage capacity could be achieved, while alleviating CO2 leakage hazards and potentially decreasing the number of injector wells. Exploiting fill-and-spill fairways for CCS is a new concept with vast worldwide applicability.