Following the discovery of oil in Paleocene sandstones in the Foinaven and Schiehallion fields in 1992 and 1993, exploration in the Faeroe-Shetland Basin has been very active. Most of the basin has been covered with 3D seismic surveys and numerous wells have been drilled for the Paleocene deep water play. However, success in terms of commercial discoveries has been limited. Detailed analysis suggests that the Foinaven/Schiehallion geological setting is unique in terms of hydrocarbon charge history, reservoir quality and trapping style. Oil charge is attributed to the presence of a Mesozoic high (Westray Ridge), which both focused charge and retained oil prior to remigration into Paleocene traps. The T35-T36 sequence which includes the Andrew Tuff appears to provide an effective top seal across the basin and all significant discoveries have been made in the T31-T35 fairway directly underlying it. Although reservoir sandstones similar to those found in the Foinaven and Schiehallion area have been encountered across the entire Faeroe-Shetland Basin, their relatively shallow burial depth and their position at the base of slope at Foinaven and Schiehallion appears to be unique in the basin. Several gas discoveries have been made in the Flett Sub-basin, located to the northeast of the Foinaven/Schiehallion area. The Flett Sub-basin has all the ingredients of a successful Paleocene hydrocarbon play, such as pervasive charge, an effective regional top seal, and stacks of Lower Paleocene deep-water sandstones and shales. However, trap definition is difficult: most remaining structures rely on a stratigraphic trapping component. The definition of top reservoir sand on seismic data is not straightforward, as seismic imaging techniques, including direct hydrocarbon indicator (DHI) analysis, are often ambiguous. T31-T35 sandstones in the deep Flett Subbasin tend to be tight, although a considerable number have been found to have good reservoir properties. Prediction of areas where reservoir quality is preserved will be a main challenge for continuing exploration in the deep part of the Faeroe-Shetland Basin, including the undesignated area adjacent to Quadrant 204. LAMERS, E. & CARMICHAEL, S. M. M. 1999. The Paleocene deepwater sandstone play West of Shetland.
Since the advent of North Sea exploration, a variety of new advances have been made in understanding basin dynamics and regional variations in structural style that are well-founded on the stratigraphy of the better known basins. New insights have also been made into the influence of Palaeozoic compressional and inversion tectonics on the structure of Mesozoic successor basins. This paper, based in part on these advances, offers a new, post plate tectonics, model for the structural and stratigraphic development of Mesozoic and Tertiary basins between mid-Norway and the Bay of Biscay.The tectono-stratigraphic evolution of this region can now be simply described in terms of a southward propagating ‘Arctic’ rift and a northward propagating ‘Atlantic’ rift. These rifts, formed by polyphase extension, remained largely separate entities until the Late Jurassic or Early Cretaceous. Thereafter, the rifts and their successor basins became a single entity represented by the Rockall Trough, Faeroe–Shetland Basin and Møre Basins only modified by later Cretaceous events and the Early Tertiary break-up of the North Atlantic and Norwegian–Greenland Sea.The ‘Arctic’ rift was initiated possibly as early as the Late Palaeozoic, nucleating on Caledonian and Late Devonian structures in the strike-parallel Caledonian terranes. Polyphase extensional events between the Permo-Triassic and Late Jurassic with intervening phases of passive subsidence resulted in rifts and basins of opposing polarity, sometimes superposed or offset, trending from the Barents Sea into the greater North Sea area.In contrast, the ‘Atlantic’ rift was probably initiated by rifting between North America and Africa in Late Triassic to Early Jurassic times. Its northward propagation was at first limited by the E-W and NE-SW Hercynian and Caledonian terranes of the British Isles and northeast Canada. The main subsequent major phase of extension initiated in the Late Jurassic and continuing through the Early Cretaceous progressively opened the North Atlantic from south to north through into the Bay of Biscay.The northward propagation of the Atlantic rift from Biscay into the Rockall Trough and Faeroe–Shetland Basin–Møre Basin completed the linkage to the Arctic rift possibly as early as the Late Jurassic and certainly by the Albo–Aptian. The ensuing rift, underlain by highly stretched continental crust, extended from the Barents Sea via the Vøring Plateau, Møre Basin into the Rockall Trough.The subsequent Late Cretaceous history of the linked system of rifts is characterized by both extension and inversion of unknown origin. In the Early Tertiary, rifting associated with voluminous volcanism along the entire margin and on the scale of the Deccan Traps heralded the break-up by spreading of the Norwegian–Greenland Sea and the northern North Atlantic. A subsequent phase of rifting elevated the Jameson Land Basin of East Greenland exhuming major oil accumulations. In contrast, co-eval phases of inversion in the Vøring Basin, Møre Basin and the Faeroe–Shetland Basin have had a positive impact on prospectivity. Inversion in the Celtic Sea is more probably related to the Pyrennean orogeny.The model of ‘Arctic’ and ‘Atlantic’ rifts offers a new and simpler predictive model of source and reservoir distribution. In the ‘Arctic’ rift, i.e. the North Sea, West of Shetland and offshore Norway–Greenland, volumetrically significant source-bed systems are confined to the Permo–Triassic, Toarcian, Middle and Late Jurassic. In the ‘Atlantic’ rift, between the Celtic Sea, Iberia and the Grand Banks, the major sources seem to be of Toarcian and Late Jurassic age. Cretaceous source beds are minor in the linked rift. However, the multiple phases of rifting and later burial or inversion history have severely affected the maturity of the Jurassic, although appeal to remigration is clearly necessary in the Faeroe–Shetland Basin.Distribution of the major reservoirs in both rifts can be best understood in relation to phases of rift propagation and subsequent subsidence. Thus, the early rifts and their immediate successor passive basins are characterized by shallow marine sedimentation. In contrast, the Late Jurassic-Early Cretaceous rifts were subject to stretching that resulted in initially deep marine environments and very thick infill of later Cretaceous sediments. Significant sand input to the linked rifts only began in the Early Tertiary as a result of the uplift and unroofing of Scotland that heralded the opening to the North Atlantic.
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