Early Tertiary evolution and sequence stratigraphy of the Faeroe-Shetland Basin: implications for hydrocarbon prospectivity

Abstract

Eight seismically resolvable packages have been identified in the Early Tertiary succession of the Faeroe-Shetland Basin. These packages are calibrated with the microfaunal and microfloral biostratigraphy, thus allowing correlation between wells and comparison with other basins. Mapping of the facies distribution within each package has allowed a detailed understanding of the evolution of the southwestern part of the basin, including the Quad 204 acreage. The development of the area can be related to the plate tectonic evolution of the North Atlantic and has highlighted implications for hydrocarbon exploration. In the earliest part of the Palaeocene (Sequences T10–T32) the position of the shelf/slope break was controlled by the underlying end Cretaceous fault induced topography. The depositional character of the submarine fans which accumulated in the basin is aggradational, collecting in basin floor deeps and progressively onlapping basin floor highs. Reservoir quality is initially controlled by depositional facies but is, essentially, excellent. Basinal muds, particularly regionally extensive maximum flooding surfaces, are believed to provide effective seals. Sequences T36–T40 are progradational in character, the position of the shelf/slope break advancing significantly beyond the positions of underlying Cretaceous fault scarps. This change in depositional character is related to thermal doming and rifting in the North Atlantic. The results of this uplift in the Faeroe-Shetland Basin also instigated a change in sediment provenance, volcanism and the deposition of extensive base-of-slope fan systems. Reservoir effectiveness remains excellent in these fan systems and potential seals are provided by downlapping, progradational shelf/slope systems. Sequences T45 and T50 represent flooding of the Palaeocene shelf systems as the thermal dome collapsed and rifting progressed. The overall control on Early Tertiary reservoir effectiveness in the Faeroe-Shetland Basin is depth of burial. In this part of the basin the Early Tertiary reservoir sands are generally buried at depths less than 2.5 km below sea-bed and reservoir quality remains excellent (porosity > 25% and permeability > 100 Md). The challenge to the oil industry is to understand the charge of this attractive hydrocarbon play.