Petroleum Systems of the Russian Western Arctic Basins

Abstract The structure of the Arctic Eurasian basins suggests that petroleum systems of Palaeozoic, Mesozoic and Cenozoic age may be present. Palaeozoic petroleum systems are well studied in the northern part of the Timan-Pechora. On the Barents-Kara shelf Palaeozoic petroleum systems are forecast, but no related hydrocarbon accumulations have been discovered, although the Palaeozoic section contains source rocks able to generate hydrocarbons. Mesozoic petroleum systems are studied in the Barents Sea and the Yamal Peninsula. They relate to Lower, Middle and Upper Triassic gas and oil source rocks, Middle Jurassic oil and gas source rocks and very rich Upper Jurassic oil source rocks. The formation of the petroleum systems and the oil and gas potential of the basins is directly dependent on the basins' structure and geological history. Palaeozoic intracratonic rifting increased the heat flow of the basin and resulted in oil and gas kitchens in the extensional parts of the basins. Fault tectonics allowed vertical migration of fluids. In the deep sag basins, like the Central Barents, South Kara and North West Siberia basins, filled by both Palaeozoic and Mesozoic strata the Mesozoic petroleum systems provide significant volume of hydrocarbon, but they are influenced by Palaeozoic petroleum systems. In the Palaeozoic basins, such as Timan-Pechora, Svalbard and, probably, North Kara, the petroleum systems are linked with hydrocarbon migration from the deep Palaeozoic horizons or adjacent Mesozoic basins. Hydrocarbon generation started long before the present basins' structural configuration formed, and oil and gas kitchens were associated mainly with extensional parts of the basins. Later phases of rifting and extension affected both the ancient oil and gas kitchens and the younger ones. Inversion caused trapping and affected fluid migration, mixing the petroleum systems. Inverted structures in the old rifts have the highest potential for large hydrocarbons accumulations but, in highly uplifted areas affected by faulting and erosion, exploration risk is high. Forecasting hydrocarbon distribution needs profound understanding of the geological evolution of petroleum basins, their structural units and petroleum systems, which control the location of giant fields. Introduction The Russian Western Arctic Basins cover the huge area including the Barents and Kara seas, the western part of the Laptev sea and adjacent territories with some archipelagoes and islands (Spitsbergen, Franz Josef Land, Severnaya Zemlya, Novaya Zemlya, etc.). They comprise the Barents and Kara Basins, the northern areas of the Timan-Pechora Basin, the North West Siberia, including Yamal and Gidan peninsulas and the Yenisey-Khatanga Basin (Fig. 1,2). The Russian Western Arctic Shelf Basins are potential for exploration of hydrocarbons as confirmed by the discoveries of the giant and large gas fields like Shtokmanovskoye in the Barents Sea, Rusanovskoye and Leningradskoye in the Kara Sea, gas condensate fields on the Yamal peninsula, oil and gas fields in the Pechora Sea and Yenisey-Khatanga basin. All the sedimentary basins on the Arctic Shelf have an intracratonic setting and have been formed by several phases of tectonism (Fig. 3). All of them are deep extensional basins (sag basins), where sediments are 8 – 15 km thick or more. The base of the crust (" Moho?? boundary) varies from 40-42 to 33-35 km. The basins are filled by mainly Palaeozoic and Mesozoic sedimentary successions. Cenozoic successions are thick and prospective only on the continental margin slopes.