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Keith Dewing, Geological Survey of Canada (Canada)
Mark Obermajer, Geological Survey of Canada (GSC) (Canada)
Gordon Oakey, Geological Survey of Canada (GSC) (Canada)
Christopher Harrison, Geological Survey of Canada (Canada)
Stephen Grasby, Geological Survey of Canada (Canada)
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The Sverdrup Basin, occupying the northern Canadian Arctic Islands, is estimated to contain 25% of Canada's discovered gas reserves. New research indicates significant remaining potential in plays and settings untested during previous exploratory work which ended in 1985.
The basin originated by rifting in the Carboniferous and included significant evaporite deposition. Sedimentation continued to the Cretaceous. Widespread gabbro intrusion related to Alpha Ridge spreading occurred in the Early Cretaceous. Younger events affecting the basin were buried by clastic sediments derived from the Eurekan Orogen in the Paleocene followed by Eocene thrust-folding. There are active and fossil thermogenic methane seeps associated with salt diapirs, and much of the known hydrocarbon resource is associated with unroofed salt domes. Pre-migration structure in the basin is related to these features and new exploration will likely focus on traps and seals associated with allochthonous salt.
A large thermal maturity dataset has been compiled from Rock-Eval pyrolysis and vitrinite reflectance analyses of subsurface and surface samples. Subsurface shale thermal maturity correlates with sonic velocity, indicating a uniform response to thermal stress with depth for Mesozoic strata. Thermal maturity was established at the level of the widespread Upper Triassic Gore Point Member; a good seismic reflector, also in close proximity to the two main oil-prone source rocks in the basin. The Gore Point Member is in the gas window (Ro>1.35%) in the northeastern part of the Sverdrup Basin. The thermal maturity is low along the northern rim of the Sverdrup Basin; an area of potential economic interest, as yet entirely unexplored. The maturity of the Gore Point Member does not exceed 1.2 Ro % in the western Sverdrup Basin. Based on these observations, large quantities of gas found at the Drake, Hecla, and Whitefish fields must have derived from a deeper source, either in Triassic or Permian strata. Traps in sandstone of the Lower Triassic Bjorne Formation may be prospective for natural gas where they are covered by an effective seal.
Given that vitrinite reflectance cannot decrease after it is set, it is possible to determine which samples have been uplifted by comparing the depth inferred from vitrinite reflectance to the current depth of burial. A normal burial curve is established using boreholes drilled in areas with no structural complexity. Low amplitude structures, including the Drake, Hecla and Whitefish fields, show little or no uplift following maximum burial in the Paleocene, indicating that these structures formed prior to the Eocene folding related to the Eurekan Orogeny. Because they were present at the time of maximum burial, they were available to be charged during hydrocarbon migration. In contrast, high amplitude structures show evidence of large uplifts following maximum burial. They formed in the Eocene and hence post-date most hydrocarbon migration.
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