ABSTRACT: Pool Entrapment in Devonian Keg River and Muskeg Dolomitized Sequences, Comet Platform, Western Canada

MUIR, IAIN D., Esso Resources Canada Ltd., Calgary, Alberta, Canada, and JEFFREY J. DRAVIS, Consultant and Rice University, Houston, TX

Keg River and Muskeg pools on Comet Platform are combination structural-stratigraphic-diagenetic traps whose reservoir facies are controlled by physiographic and tectonic setting.

Reservoir facies are confined principally to platform-interior, restricted subtidal Amphipora-peloidal dolopackstones and dolowackestones. They are part of 7-12 m thick depositional cycles correlatable across Comet Platform. Best reservoir zones occur at or near the bases of these major cycles. Reservoir quality resulted from dissolution of burial dolomites: Keg River is dominated by spectacular Zebra dolomites with vuggy porosity; Muskeg dolomites exhibit moldic and vuggy porosities. Termination of stylolites and fractures into these secondary pore types confirm their burial origin.

Regional and local tectonic influences on pool development are reflected by the presence of horizontal fractures, vertically oriented stylolites, and spectacular burial solution-collapse breccias. Pools are localized over regional fault and fracture trends related to reactivation of the Great Slave Lake shear zone. Faults and fractures aided burial diagenesis and late secondary porosity development by moving vertically hot, basement-derived and calcium-rich fluids, which facilitated dolomite dissolution. Seismic data indicate these faults were generated by salt withdrawal in the underlying Cold Lake Salt. Further, some of these faults localized massive diagenetic anhydrites that provided side closure for some pools. Dissolution by hot, basement-derived fluids is supported by the prese ce of diagenetic fluorites, megaquartz and polysulfide minerals, helium gas, fluid inclusions, and high carbon dioxide and hydrogen sulfide gases in these pools.

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