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TitleOil migration driven by exhumation of the Canol Formation oil shale: a new conceptual model for the Norman Wells oil field, northwestern Canada
AuthorHadlari, T
SourceMarine and Petroleum Geology vol. 65, 2015 p. 172-177,
Alt SeriesEarth Sciences Sector, Contribution Series 20140333
Mediapaper; on-line; digital
File formatpdf
ProvinceNorthwest Territories
AreaNormal Wells
Lat/Long WENS-126.5083 -126.0000 65.5083 65.0000
Subjectsfossil fuels; stratigraphy; structural geology; hydrocarbons; hydrocarbon recovery; oil; oil analyses; oil migration; oil shales; petroleum; petroleum exploration; petroleum resources; fractures; earth thermal history; Canol Formation
Illustrationslocation maps; plots; cross-sections
ProgramMackenzie Corridor, Shield to Selwyn, GEM2: Geo-mapping for Energy and Minerals
AbstractThermal history, petroleum system, structural, and tectonic constraints are reviewed and integrated in order to derive of a new conceptual model for the Norman Wells oil field, and a new play type for tectonically active foreland regions. The thermal history recorded by Devonian rocks suggests that the source rocks experienced peak thermal conditions in the Triassic-Jurassic, which is when oil was likely generated. After oil generation and expulsion the Canol Formation, which is an oil shale, retained a certain fraction of hydrocarbons. The shallow reservoir (650-350 m) is a Devonian carbonate bank overlain by the Canol Formation and resides within a fault block in a hanging wall position to the Norman Range thrust fault. Both reservoir and source rocks are naturally fractured and have produced high API non-biodegraded oil. Thrust faults in the region formed after the Paleocene, and a structural cross-section of the field shows that the source and reservoir rocks at Norman Wells have been exhumed by over 1 km since then.
The key proposition of the exhumation model is that as Canol Formation rocks underwent thrust-driven exhumation, they crossed a ductile-brittle transition zone and fractures formed sympathetic to the thrust fault that were oriented in a dip-direction. The combination of pore overpressure and new dip-directed subvertical fractures liberated oil from the Canol Formation and allowed for up-dip oil migration. Reservoir rocks were similarly fractured and improved permeability enhanced charging and pooling of oil. GPS and seismicity data indicate that strain transfer across the northern Cordillera is a response to accretion of the Yakutat terrane along the northern Pacific margin of North America, which is also the probable driving force for foreland shortening and rock exhumation at Norman Wells.
Summary(Plain Language Summary, not published)
Norman Wells has been a very prolific oilfield and presents an interesting puzzle with apparently contradictory datasets. Exploration in the central Mackenzie region has been guided by a conventional model for Norman Wells, which has been unsuccessful. This manuscript presents a new model proposing that the oil had resided in the Canol Formation since the Triassic and has been liberated by a natural "fracking" process triggered by relatively recent thrust-fault activity. As a significant departure from the old conventional model, which looked for undisturbed reefs (that were drilled, unsuccessfully), the new model would guide exploration toward active thrust faults in the region.