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Oil and gas exploration in the northern North Sea and the southern Norwegian shelf has mainly been concentrated on Jurassic and younger reservoirs with Late Jurassic black shale source rocks. New onshore investigations in Jameson Land, central East Greenland, suggest that the Permian of the Norwegian-Greenland Sea margins contains relatively thick sequences of potential oil source rocks interbedded with carbonate reefs.
The East Greenland, Upper Permian marine basin is exposed over a length of 400 km (250 mi) from Jameson Land in the south to Wollaston Forland in the north, parallel with the continental margin. The maximum width of the onshore part of the basin is 200 km (125 mi), and the maximum thickness of preserved sediments is about 300 m (1,000 ft). The Upper Permian lies unconformably on faulted, tilted, and peneplaned Lower Permian red beds or older rocks. The Upper Permian sediments are indicative of a transgressive sequence. Initial sedimentation in the marginal parts of the basin are characterized by evaporites and hypersaline carbonates, whereas normal marine carbonate and black shale prevail in the more offshore parts of the basin. Continued transgression led to the development of normal marine conditions throughout the basin and carbonate reefs were formed over structural highs. Black shale rich in organic matter was deposited under anaerobic to dysaerobic conditions between and around the reefs. Toward the end of the Permian, reef growth ceased and many reefs were draped by black shale that finally gave way to coarser grained, carbonaceous sandy shale, deposited under well-oxygenated normal marine conditions. A very short but marked regression took place at the Permian-Triassic boundary, so that along basin margins and over structural highs, the top of the Permian was eroded. Subsequently, the Early Triassic sea transgressed the area and deposition of marine sandstone and shale continued. The Triassic shale is reminiscent of the Upper Permian shale, but the organic con ent of the former is low and mainly of terrestrial origin (spores and pollen). Accordingly, the Triassic shale has no source rock potential. Following the Early Triassic marine interlude, a major regression took place. The remaining part of the Triassic was characterized by intermontane graben deposition of alluvial fan, fluvial, eolian, and lacustrine red beds.
The Upper Permian black shale is relatively thick, widely distributed, has a high organic carbon content, and a favorable kerogen type. According to vitrinite reflectance and pyrolysis data, it is premature to slightly mature in the surface exposures along the basin margin. If buried under 2-3 km (6,500-9,800 ft) of younger sediments, as is expected in the onshore and offshore basins, the shale will most probably be developed as a mature source rock for oil. It is interbedded with and overlies carbonate reef and platform sequences that have undergone several periods of karstification in some areas. This karstification may have enhanced the reservoir potential considerably. The Upper Permian shale has a combined source rock and seal potential, and uppermost Permian and Lower Triassic c arse sandstone interbedded with the shale may also have reservoirs properties. The Lower Triassic also contains several tight shale and evaporite units that may function as seals. In the northern North Atlantic area, the Early to Middle Triassic was a period of rifting activity; thus, combined structural-stratigraphic traps are an obvious exploration target. Consequently, the possibilities for a Permian play in the northern part of the Norwegian shelf and along parts of the Norwegian-Greenland Sea margins are worth evaluating.
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