Structural characterization and across-fault seal assessment of the Aurora CO ₂ storage site, northern North Sea

Abstract

Faults play an essential role at many potential CO 2 storage sites because they can act as conduits or barriers to fluid flow. To contribute to the evaluation of the Aurora storage site in the northern North Sea, we perform a structural characterization and assessment of across-fault seals that displace the Lower Jurassic storage complex. We find that first-order faults are predominately north–south striking and west dipping, with throws greater than the thickness of the primary seal (>85 m). In contrast, second-order faults have lower throws (15–50 m), and variable strike and dip directions. Due to the dip of the storage complex, injected CO 2 is likely to migrate northwards before encountering the first-order Svartalv Fault Zone on its footwall side, which juxtaposes the storage units against younger sand-rich units. However, shale gouge ratio values exceed 0.30 at the depth of the storage complex, suggesting that a fault membrane seal may be present. Furthermore, second-order NE-dipping faults create juxtaposition seals and, in places, small-scale structural traps (24–48 m) along the Svartalv Fault Zone. Overall, we suggest that faults within the Aurora storage site could provide barriers to plume migration, allowing more CO 2 to become trapped and thereby increasing the storage capacity. Thematic collection: This article is part of the Energy Geoscience Series available at https://www.lyellcollection.org/cc/energy-geoscience-series