The occurrence of faults in the Bunter Sandstone Formation of the UK Sector of the Southern North Sea and the potential impact on storage capacity

The Triassic Bunter Sandstone Formation of the Southern North Sea is believed to have significant potential to store CO2 for climate change mitigation [1]. It has fair to good reservoir properties and a seal is provided by the mudstones of the Triassic Haisborough Group. It has been folded into domes and periclines (henceforth Bunter domes) by the post depositional late Triassic to Tertiary movement of the underlying evaporites of the Zechstein Group. These domes have been identified as targets for CO2 storage as they are very large and at least some of them have the ability to retain buoyant fluids, demonstrated by the presence of gas fields in some domes [2], [3], [4], [5] (though the majority of the formation is saline water-bearing). However, faults have been identified within the Haisborough Group cap rock directly above a number of the Bunter domes. The faults are thought to have formed as result of extensional stresses exerted during dome formation. They may have an impact on storage site security, as they could act as migration pathways for CO2 out of the storage site and therefore limit the number of Bunter domes that could be utilised for storage of CO2. This study considers the occurrence of faults in the cap rock above the Bunter domes and the potential impact on static capacity estimates.