Onshore field mapping and core data reveal drainage system pathways during Basaltic Plains Volcanism: Implications for unconventional intra-volcanic plays along the NW European Margin

The opening of the North Atlantic Ocean was associated with the vast outpouring of predominantly subaerial flood basalt lava flows. This Paleogene volcanism is found along the NW European margin, a passive continental margin that extends from the western Barents Sea to offshore west of Ireland. This includes the Faroe-Shetland Basin, whose north-west side is blanketed by the Paleocene-Eocene (T40-T45 Sequences) Faroe Islands Basalt Group (FIBG) that covers an area of >120,000 km² and is locally up to 5 km thick. There are many exploration challenges associated with the volcanic succession, such as the well-documented seismic imaging problem, but also technological difficulties posed in drilling heterogeneous volcanic sequences. Despite these challenges, plays were initially targeted beneath the FIBG, following Paleocene discoveries beyond the extent of the subaerial volcanism (e.g. Foinaven & Schiehallion). In aiming to find these potential sub-volcanic reservoirs (e.g. T30 Sequence sandstones) an unexpected intra-volcanic discovery was made in 2004, namely the Rosebank Field (~240 MMBOE) that is now looking to be developed. The reservoirs belong to the younger Colsay Sandstone Member (T40 Sequence) of the lower Flett Formation, which consist of braided fluvial and intermixed fluvial-deltaic siliciclastic sandstones interbedded with subaerial lava flows and volcaniclastic rocks. To the south-west of Rosebank an additional supra-volcanic discovery was made in the Hildasay Sandstone Member (T45 Sequence) from the upper part of Flett Formation with the possibility that these deltaic sandstones may also be interbedded with the volcanic succession elsewhere.

These discoveries have led to a renewed interest in the interplay between volcanism and sedimentation, ranging from lava-sediment interactions to the development of intra-volcanic drainage systems. A remnant of the FIBG, that hosts the intra-volcanic discoveries, is only exposed on the Faroe Islands, an archipelago of 18 main islands with an areal extent of ~1400 km². The islands are situated ~200 km north-west of the discoveries and although no siliciclastic sandstones have been found, they do contain volcaniclastic sandstones deposited by analogous fluvial systems.