Inter-Basalt Prospectivity at Elongated Ridges in the NE Atlantic

Summary The discovery of the Rosebank oil and gas field in the NE Atlantic has identified inter-basalt reservoirs as significant targets for future exploration. Top and Base Basalt and numerous overlying amplitude anomalies are mapped on 3D seismic data in two study areas: West of Shetland (UK) and the outer Voring Basin (Norway). We describe seven undrilled elongated ridge structures which are defined at Top Basalt level. Above these ridges are stacked amplitude anomalies interpreted to be caused by hydrocarbon leakage. In the Voring Basin seabed sampling finds that both oil and gas seeps occur at the seabed above these anomalies. In the West of Shetland area, well data from Tobermory (214/4-1) and Bunnehaven (214/9-1) as well as a seismic well-tie indicates that the basalt sequences at the two wells are diachronous. Seismic interpretation shows that the basalt sequences overlie each other and that a clastic sand-rich unit observed at both wells potentially extends between the basalt units. Four of the basalt ridges occur where the sand-rich unit observed at the two wells could be an inter-basalt reservoir. Overlying amplitude anomalies suggest the reservoir may be charged.