ABSTRACT

The Trout Field (Tp. 89 Rge. 3 W5M) produces oil from the Middle Devonian Elk Point Group Keg River Formation. Regional mapping shows that the Trout is located between the eastern margin of the Keg River 'Bank Edge' and the western pinchout against the Peace River Arch. The Keg River isopach shows a wedge of carbonates thickening from the Peace River Arch to the 65m-thick 'Bank Edge'. The Keg River Reservoir is composed of dolomites that lie conformably between the Chinchaga anhydrite facies and the younger Muskeg evaporite sequence. It occasionally overlies the Precambrian erosional surface. From Trout to Senex (Tp. 96 Rge. 6 W5M), the Precambrian topography has discontinuous northwest trending en echelon ridges, which influenced Keg River deposition. Several stages of tectonism have readjusted the Precambrian topography to a present-day southwest dipping surface upon which relict Precambrian ridges remain.

Flooding over the Chinchaga during Lower Keg River time left an expansive argillaceous carbonate unit overlapping Precambrian islands. Rare stromatoporoids in this unit indicate a deeper water facies not capable of supporting reef-associated organisms. Microkarst topography at the top of this unit suggests bathymetric fluctuation and subaerial exposure. Middle and Upper Keg River carbonates are a succession of shallow water shoals supporting large communities of reef-associated fauna, predominantly tabular and encrusting stromatoporoids, and dendritic Amphipora, with cyclindrical and large colonial corals. Precambrian topographic highs provided the substrate for shoaling while regional paleo wind-wave patterns influenced major Keg River lithofacies distribution.

Porosity development was by matrix-selective early dolomitization of original limestone with later dolomitization of stromatoporoids and corals. Porosity development is facies specific with those facies that exhibit abundant biotic diversity having greater vuggy and moldic porosity. Intercrystalline porosity is prevalent in grainstone facies and in sandy lithic reefal facies. Fracture porosity occurs predominantly in fine crystalline dolomites with little or no matrix porosity.

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