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Berlin, Techn. Univ., Diss., 2014. - 3D petroleum system modelling; geochemistry; glacial cycles; hydrocarbon leakage; Barents Sea
Abstract:
The 3D basin modelling of the Southwestern Barents Sea was planned with the aim of addressing the masses of petroleum generated, migrated, accumulated and lost during the basin evolution. The first model was constructed for the Hammerfest Basin considering three source rocks, which correspond to the Upper Jurassic Hekkingen Formation and the Triassic Snadd and Kobbe formations. The highest maturities for the three source rocks were reached in the western and northwestern margin of the basin. The model reproduced satisfactorily the hydrocarbon phases and distribution of the main fields and discoveries. Two events of petroleum re-distribution occurred in the basin: the first corresponds to the oil re-distribution (during the Oligocene–Miocene); the second corresponds to the gas leakage (during the Pliocene–Pleistocene) in connection to the glacial–interglacial cycles. At least 0.247 Gt of thermogenic gas leaked from the main reservoir and reached the sediment interface. The analysis of the volumetric proportions of oil and gas contributions to each field and discovery, suggest that the gas contribution stems mainly from Triassic source rocks, while the oil phases contain variable proportions from both the Jurassic Hekkingen Formation and the Triassic source rocks. Available fluid geochemical data from the main fields in the Hammerfest Basin allowed testing these results. The interpretation of gas isotopes and maturity related biomarker ratios confirms the maturity trends derived from basin modelling; and light hydrocarbons indicate the influence of secondary processes. However, age related biomarker ratios did not provide a clear separation when evaluating a contribution from Jurassic versus Triassic source rocks.
The 3D basin modelling was extended to include the Loppa High as well as some other important frontier exploration areas; taking into account the same source rocks. Calibrated model predictions indicate that the three source rocks are overmature in the western margin and also have high maturities in the deepest parts of the Maud Basin to the east. However, in the Bjarmeland platform, only the Triassic source rocks have entered the oil window. Recent generation has been observed in the eastern part around the Bjarmeland Platform and generative potential is still available at present–day. The timing of generation in the western part is different in comparison to the east, with the Kobbe Formation starting to generate during the Late Triassic–Early Jurassic, the Snadd Formation during Late Jurassic–Early Cretaceous and the Hekkingen Formation during Middle Cretaceous. The three source rocks do not have any generative potential left; therefore, it is necessary to rely on younger source rocks. Additional results indicate that the main drainage directions do not change drastically during the evolution of the area, not even during the glacial–interglacial cycles. The model output shows changes in the sizes of the relative oil versus gas quantities in the modelled accumulations during the glacial cycles.
