IMPACT OF MAGMATISM ON PETROLEUM SYSTEMS IN THE SVERDRUP BASIN, CANADIAN ARCTIC ISLANDS, NUNAVUT: A NUMERICAL MODELLING STUDY

S.F. Jones1*, H. Wielens2, M-C. Williamson2 and M. Zentilli3

1 Department of Geology and Geophysics, University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canada.

2 Geological Survey of Canada (Atlantic), PO Box 1006, Dartmouth, NS, B2Y 4A2 , Canada.

3 Department of Earth Sciences, Dalhousie University, Halifax, NS, Canada.

* author for correspondence, email: sfjones@ucalgary.ca

Numerical modelling is used to investigate for the first time the interactions between a petroleum system and sill intrusion in the NE Sverdrup Basin, Canadian Arctic Archipelago. Although hydrocarbon exploration has been successful in the western Sverdrup Basin, the results in the NE part of the basin have been disappointing, despite the presence of suitable Mesozoic source rocks, migration paths and structural/stratigraphic traps, many involving evaporites. This was explained by (i) the formation of structural traps during basin inversion in the Eocene, after the main phase of hydrocarbon generation, and/or (ii) the presence of evaporite diapirs locally modifying the geothermal gradient, leading to thermal overmaturity of hydrocarbons. This study is the first attempt at modelling the intrusion of Cretaceous sills in the east-central Sverdrup Basin, and to investigate how they may have affected the petroleum system.

A one-dimensional numerical model, constructed using PetroMod9.0, investigates the effects of rifting and magmatic events on the thermal history and on petroleum generation at the Depot Point L-24 well, eastern Axel Heiberg Island (79o2340N, 85o4422W). The thermal history is constrained by vitrinite reflectance and fission-track data, and by the tectonic history. The simulation identifies the time intervals during which hydrocarbons were generated, and illustrates the interplay between hydrocarbon production and igneous activity at the time of sill intrusion during the Early Cretaceous. The comparison of the petroleum and magmatic systems in the context of previously proposed models of basin evolution and renewed tectonism was an essential step in the interpretation of the results from the Depot Point L-24 well.

The model results show that an episode of minor renewed rifting and widespread sill intrusion in the Early Cretaceous occurred after hydrocarbon generation ceased at about 220 Ma in the Hare Fiord and Van Hauen Formations. We conclude that the generation potential of these deeper formations in the eastern Sverdrup Basin was not likely to have been affected by the intrusion of mafic sills during the Early Cretaceous. However, the model suggests that in shallower source rocks such as the Blaa Mountain Formation, rapid generation of natural gas occurred at 125 Ma, contemporaneous with tectonic rejuvenation and sill intrusion in the east-central Sverdrup Basin. A sensitivity study shows that the emplacement of sills increased the hydrocarbon generation rates in the Blaa Mountain Formation, and facilitated the production of gas rather than oil.

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