ALBERT

Description: 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.

Description: The Barents Sea is a frontier for hydrocarbon exploration where activity has been renewed after recent oil discoveries. However, previously this province has been dominated by gas finds, with the largest discoveries being Snøhvit, Albatross and Askeladd gas fields, located in the Hammerfest Basin. Cenozoic erosion and high latitude Quaternary glaciations are thought to have driven the hydrocarbons out of the traps and contribute thus to the lack of significant oil discoveries. Hydrocarbon leakage is a widespread phenomenon and has significant impact on climate, marine ecosystem, geotechnical installations and petroleum exploration. In this study, we aim to elucidate the impact of Cenozoic erosion and Pliocene-Pleistocene glaciations on the dynamics of hydrocarbon leakage from the thermogenic reservoirs. We use high resolution and vintage 3D seismic reflection datasets to analyse hydrocarbon plumbing system above the Snøhvit and Albatross gas fields to investigate the geo-morphological manifestation and the dynamics of leakage from the reservoir. We then use 3D Petroleum Systems Modelling (PSM) to simulate the basin history in terms of generation, migration and leakage of hydrocarbons through time in response to erosion, glacial loading and deglaciations. Based on this integrated approach, we then are able to compare numerical modelling results with seismically observed leakage indicators. Numerous EW trending reactivated faults are present in the study area which link the Jurassic hydrocarbon reservoirs of the Snøhvit and Albatross field with the shallow Paleocene strata. Reactivation of polygonal fault networks has formed an interconnected network of Paleocene faults, which served as migration avenues for thermogenic fluids in the vicinity of deep reactivated tectonic faults. Numerous pockmarks and mega pockmarks on the seabed and buried pockmarks on the base Quaternary Upper Regional Unconformity (URU) provide evidence of migration pathways as they are connected to seismic blow out pipes, Paleocene fault networks and deep reactivated tectonic faults. A gas cloud anomaly has been interpreted as a Bottom Simulating Reflector (BSR), whose depth coincides with the estimated base of the hydrate stability field for a thermogenically-derived gas hydrate with around 90 mol % methane. At least two fluid venting episodes have been inferred based on seabed and URU pockmark distributions, following the Last Glacial Maximum ~17-16 ka and prior to the Late Weichselian, older than ~0.7 Ma. Results of the 3D PSM modelling show that hydrocarbon leakage from the Jurassic reservoirs takes place through faults during each deglaciation, with most of accumulated mass lost (60-80 %) during the first instance of fault dilation. Subsequent leakage during deglaciations results in a sequential loss of remaining accumulated mass in the Snøhvit reservoir. The first modeled leakage event (0.8-0.78 Ma) coincides with a major fluid escape event at the time of a major regional unconformity (URU older than ~0.7Ma), and is in agreement with shallow subsurface hydrocarbon leakage indicators such as pockmarks, shallow gas clouds and blow out pipes observed in the seismic data analysis.