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TitreGeology of the Bent Horn Oil Field, Cameron Island, Nunavut
AuteurDewing, K; Wendte, J
SourceNunavut Petroleum Symposium, abstracts; .
Séries alt.Secteur des sciences de la Terre, Contribution externe 20120215
RéunionNunavut Petroleum Symposium; CA
Lat/Long OENS-105.0000 -102.0000 77.0000 76.0000
Sujetschamps de pétrole; méthodes d'exploration; puits d'exploration; antécédents géologiques
Illustrationsschematic models; schematic representations; location maps; cross-sections
ProgrammeBassin sédimentaire Sverdrup, GEM : La géocartographie de l'énergie et des minéraux
Résumé(disponible en anglais seulement)
Crude oil was discovered at Bent Horn in 1974. The reservoir is Lower and Middle Devonian reef limestone of the Blue Fiord Formation. The pool is delineated by six wells. Two wells recovered oil, one encountered an oil show and three were dry holes. The A-02 well sustained 5300 bbls/day production. Production between 1985 and 1993 was 321,470 m3. The well was shut in in 1995. Bent Horn lies within the highly structured transition zone between the lower Paleozoic Franklinian Basin and the upper Paleozoic to Mesozoic Sverdrup Basin. It occurs in the upper of two northward-directed back thrusts, sealed on the southern side by a normal fault with 300 m throw. The pool is confined on the eastern side by a facies transition from reefal carbonate to shale.
Deposition in the Arctic Islands during the Silurian to Mid Devonian was characterized by a shallow water carbonate shelf to the southeast and a deep-water shale basin to the northwest. Discontinuous reefs (Blue Fiord Formation) bordered the deep-water shale basin. The thickness of the Bent Horn carbonate buildup is 1200-1500 m. Rocks in cores are grain-supported limestones of two types: 1) floatstone and rudstone with tabular stromatoporoids and tabular tabulate corals with peloidal-skeletal grainstone or low-mud packstone matrix. These are interpreted as debris deposited on the upper portion of a reefal foreslope; 2) peloidal and skeletal grainstone and low-mud packstone with finely broken-up reef-formers, commonly micritized to form peloids, and crinoids. These low-mud packstones and grainstones are interpreted as foreslope sands deposited farther downslope. Rocks of the foreslope facies had high depositional porosities and micro-pores of dissolution origin are also present. However, all these pores are filled by calcite cement or plugged with bitumen.
Despite the lack porosity, all core pieces released an oil scum when etched. The oil is interpreted to be residual and is thought to be intermixed with the bitumen. Oil production from W. Bent Horn A-02 was from late-formed open fractures related to thrust faults. The oil is non-biodegraded with thermal maturity corresponding to the mid-late part of the oil window. Geological evidence suggests a Paleozoic source rock for this oil. Rock-Eval/TOC pyrolysis data indicate good source rock potential for the Silurian basinal facies. Based on biomarker analyses, maturity and stratigraphic and geographic proximity to the Bent Horn oil field, the Cape Phillips Formation appears to be the most likely source rock for the hydrocarbons at Bent Horn.
The limestones were buried to an estimated depth of 3 to 5 km from loading by clastic strata from Middle to Late Devonian time. Limestones of the Blue Fiord Formation were then thrusted from latest Devonian to earliest Carboniferous time, followed by rapid subsidence due to rifting related to the opening of the Sverdrup Basin between Early Carboniferous and Mid-Permian time. The migration of oil into Bent Horn is interpreted to have occurred during an episode of rapid burial and relatively high heat flow during the opening of the Sverdrup Basin. Bitumen apparently formed from the subsequent over-cooking of the oils.