--> Abstract: The Early Cambrian Tweed Lake Gas Field and Related Gas Occurrences, Northwest Territories, Canada, by J. M. Bever and I. A. McIlreath; #91012 (1992).

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ABSTRACT: The Early Cambrian Tweed Lake Gas Field and Related Gas Occurrences, Northwest Territories, Canada

BEVER, JEFFREY M., and IAN A. MCILREATH, Petro-Canada, Calgary, Alberta, Canada

Gas of a peculiar composition (mainly methane and nitrogen) and some condensate exists in Early Cambrian, shallow marine sandstones in the Interior Plains of the Northwest Territories, from the discovery well at Tedji Lake southward to Bele, a distance of over 180 km. The largest discovery, Tweed Lake, contains an estimated 112 bcf of recoverable reserves in a fault-bounded anticlinal structure.

The reservoir sandstones occur in the Mount Clark Formation, which regionally is 10 to 70 m thick, and at Tweed Lake, which consists of a basal and upper sandstone separated by a shale interval. These sands accumulated in wide, shallow lows on a peneplained (previously structured) Proterozoic sedimentary substrate between broad topographic highs, during a transgression. The sandstones are comprised predominantly of remnant, fine-medium, monocrystalline quartz grains that are variably cemented by mostly silica, authigenic clay, and dolomite. Reservoir porosity is mostly a remnant or reopened intergranular type with subsidiary secondary moldic, after feldspar dissolution. Dissolution processes appear to have continued even after emplacement and degradation of an oil phase in the basal s ndstone.

The reservoir is sealed by overlying Cambrian shales and widespread evaporites. Source rock geochemistry is unique.The source rock may be within the overlying shales of the Mount Cap Formation in horizons with relatively low amounts of organic (algal) material. The source rock and reservoir potential of the underlying Proterozoic is yet unknown.

The Tweed Lake gas field and related gas occurrences demonstrate hydrocarbon prospectivity in the related unexplored Early (Pre-Devonian) Paleozoic section of the Northwest Territories.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)