Exhumation of the Corrib Gas Field, Slyne Basin, offshore Ireland

Abstract

The Corrib Gas Field contains in excess of 10 12 SCF (28.3×10 9 Sm 3 ) of gas in place in a Triassic fluviatile sandstone reservoir, sealed by late Triassic evaporites and trapped in a relatively simple, but underfilled, NE–SW-trending anticlinal structure. In contrast, the post-Triassic overburden manifests a more complex evolution with indications of flipped polarity, extensional faulting on a crestal detachment structure during the Jurassic, succeeded by alternate episodes of burial and exhumation from the Early Cretaceous onwards. Compactional, thermal and stratigraphic frames of reference have been used to assess the magnitude and timing of the principal exhumation episode, which occurred during the early Cretaceous. Large uncertainty is associated with exhumation estimates derived from individual techniques, but stratigraphic analysis and seismic interpretation support the conclusion that kilometre-scale (800–1700 m) exhumation and erosion of the Jurassic overburden has occurred in the Corrib area. A number of post-Aptian re-burial and exhumation events also occurred but are unlikely to have exceeded the earlier maximum burial of source, reservoir and seal rocks achieved during the Late Jurassic. Continued local extensional reactivation of the listric detachment structure, post-Aptian, has resulted in a pattern of heterogeneous exhumation within the field area. However, the severely attenuated post-rift stratigraphic record throughout the Slyne Basin suggests that long-wavelength processes, such as mantle hotspot activity and shoulder uplift linked to the rifting and thermal subsidence of the Rockall Basin, were the primary drivers of exhumation in the Corrib area during the Cretaceous-Tertiary period.