The Clair Discovery, west of the Shetland Isles

Abstract

Introduction Recent exploration has heightened awareness of the hydrocarbon potential west of the Shetland Isles. Several discoveries have been announced in the past couple of years which suggest that the area may become a highly significant oil province. These finds have renewed interest in the Clair Discovery, which was originally found almost twenty years ago and contains reserves estimated to be in excess of three billion barrels of oil. Geological evolution of the Clair region At the end of the Caledonian Orogeny, following collision of the Laurentian-Greenland and Fennoscandian–Russian continental plates ([Ziegler 1988][1]), a series of 'Old Red' fault-bounded, inter-montane molasse basins developed in late Silurian to early Devonian times. A model of extensional collapse of the over-thickened crust along old Caledonian lineaments or thrusts, has been proposed by several workers ([McClay et al. 1986][2]; [Norton et al. 1987][3]; [Coward et al. 1989][4], [Seranne, 1992][5]) for these actively subsiding basins. The Clair discovery (Fig. 1) lies within the West Shetland Basin (WSB) which developed in such a tectonic setting, linked to the Shetland Spine Fault on its easterly margin (Fig. 2). Reconstruction of Devonian basins ([Duindam and van Hoorn 1987][6]) shows the WSB and the Clair area to be associated with a system of dominantly NE–SW-trending linked extensional faults. These faults separate the WSB from the main Orcadian Basin to the east by an area of uplifted basement known as the Shetland Platform. The area has been affected by several episodes of deformation including two main phases of extension . . . [1]: #ref-8 [2]: #ref-5 [3]: #ref-6 [4]: #ref-3 [5]: #ref-7 [6]: #ref-4