Sub-basalt hydrocarbon prospectivity in the Rockall, Faroe–Shetland and Møre basins, NE Atlantic

Abstract The seismic imaging below the basalts in the NE Atlantic basins is generally poor and the thickness of the basalts is difficult to predict. Two recent wells (William, 6005/13-1 and Brugdan, 6104/21-1) drilled in Faroes waters were suspended before reaching the main sub-basalt reservoir targets, because the basalts were thicker than expected. New deep-tow (18 m) seismic reflection data has now allowed more detailed imaging of the sub-basalt Mesozoic strata. The base of the basalt is not always reflective and is probably a transitional contact, with low acoustic impedance. The underlying Mesozoic strata produce coherent reflectivity. Large structural closures produced by Cretaceous rifting and Cenozoic folding have been imaged in the Rockall and Faroe–Shetland basins and these may contain Cretaceous and Paleocene clastic reservoirs at drillable depths of about 4 km. The Rockall Trough contains 4–7 km thickness of Mesozoic strata and appears to be floored by stretched continental crust throughout. The lower section may contain Jurassic source rocks similar to the areas to the south, east and north of the basin. Large Cenozoic age folds are present which produce potential traps at Late Cretaceous level, where sandstones equivalent to the Upper Cretaceous Nise Formation may occur. These folds represent some of the largest undrilled structures in NW Europe.