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AAPG Europe Regional Conference, Global Analogues of the Atlantic Margin

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Evolution and petroleum systems of the South-Barents and South-Kara basins

Abstract

The South-Barents and South-Kara basins are the two deepest sedimentary depressions in the Russian Arctic shelf. Both of them have significant proven oil and gas reserves and huge prospective resources. Though this region has been studied for over 40 years, many important geological questions remain unanswered. It is of interest to compare some principal results for the two largest basins - South-Barents and South-Kara basins, namely, similarity and differentiation of their potential source rocks and their most general evolution patterns. The principal distinction between these two basins is due to the duration of their burial: the Barents Sea basin was initiated at the end of the Early Paleozoic, whereas the South Kara basin formed since the Permian-Triassic boundary. In the South Barents Sea basin, several phases of subsidence/uplift were established, the maximum rate of sedimentation was noted in the Permian-Triassic. The South-Kara basin generally has one long cycle of subsidence with maximum velocity at the end of the Jurassic-Early Cretaceous. The deep structure of the lithosphere beneath these basins is different. In turn, this is related with the different tectonic setting of these basins. The South-Barents basin was initiated as a rift, and for a long time in the Late Paleozoic-Mesozoic it was a back-arc basin. The South-Kara basin is considered to be a part of intracontinental failed rift. Accordingly, this manifests itself in other features of the basins - the deep structure of the lithosphere and the age of the source rocks and reservoirs. Rock-Eval pyrolysis and vitrinite reflectance data were used to estimate potential source rocks in terms of their quantity, quality and thermal maturity. The four most prominent source rock intervals were distinguished for the Barents Sea Basin – Upper Devonian marine facies (Type II kerogen), Upper Carboniferous – Lower Permian marine carbonate-siliciclastic rocks Type II-III), Low-Middle Triassic shales (Type III) and Upper Jurassic black shales (Type II). The Paleozoic rocks are usually overmature, Triassic source rocks are in the oil window, and Cretaceous ones are immature as a rule. In the generalized section of the South-Kara basin from the Triassic to the Paleogene many potential oil-and-gas source rocks alternating with reservoirs and seals were recognized. However, the contribution of the Upper Cretaceous and Paleogene source rocks is unlikely, since the modeling results show that these strata didn’t reach the oil window. The most promising source rock intervals are concentrated in the Jurassic and Low Cretaceous successions. The regional modelling of these basins allowed to compile a large body of geophysical, geological data, perform their reinterpretation and obtain new analytical data. The most general features of the basins and their petroleum systems evolution were identified.