The Turonian play in the Faeroe–Shetland Basin

Abstract

Recent exploration in the Faeroe–Shetland Basin has concentrated on the Paleocene, following the successes of the Foinaven and Schiehallion fields. However, a number of deeper Mesozoic plays may still exist in the basin. This paper describes results of recent exploration activity targeted at a Turonian play in the Faeroe–Shetland Basin, west of the Rona Ridge, and discusses implications for future prospectivity in the area. The play tested is a slope fan pinchout against the Rona Ridge, comprising Cenomanian–Turonian high density turbidite sandstones. These were shed into a deep-water basin in the hanging wall of the Rona Fault during a base-level change in the adjacent West Shetland Basin. Two wells have proven considerable thicknesses of interbedded sandstones and shales in the Cenomanian–Turonian interval. Reservoir quality is locally excellent with porosities exceeding 20% and permeabilities up to 1 D. While hydrocarbon shows have been encountered, targeted prospects appear to have failed because of a lack of up-dip seal, emphasizing that the key risk for down-thrown plays against the Rona Fault remains trap integrity. The presence of both oil and gas shows though, confirms that the Turonian sandstone package has acted as a migration focus and may represent the main conduit from the deeper Jurassic source kitchen into the Clair Field. A sedimentological and diagenetic model for the sandstones based on recently acquired core data implies that clean, high quality deposits may also exist in a more basinward setting, possibly as detached fan complexes. This stratigraphic interval remains a potential play for future exploration, but with the depth of burial increasing rapidly westwards, overpressuring may be required to preserve porosity and permeability.