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.