The Duhamel oil-field, central Alberta (Twp. 45, Rge. 21, W. 4 Mer.) produces from these Upper Devonian reef sections. Photographs of 34 acetate peels of the carbonate section in Socony Duhamel 29-14 well, between 4410 and 4870 feet drilling depths, illustrate reefoid facies in the Upper Devonian Nisku and Leduc Formations. Thin section studies also include the overlying Calmar Shale, and the Ireton Shale separating the reefs.

The Calmar Shale is dark-greenish grey, calcareous, irregularly laminated, with pockets and stringers of pyrite.

The Nisku Dolomite is secondary. Algae and Amphipora indicate that deposition took place in warm, shallow, quiet marine water conditions. Anhydrite fills the vugs in the lower portion of the Nisku Formation. Porosity and permeability is relatively poor as compared to the underlying Leduc carbonates. X-ray diffraction indicates very high percentage of dolomite in the Nisku.

The Ireton Formation above the Leduc bioherm is greenish grey, fine grained dolomitic shale.

The Leduc reef is composed of light grey to yellowish grey bioclastic calcarenite and calcirudite. X-ray diffraction indicates no dolomite, though recrystallization has taken place and destroyed some of the internal structures of the organisms. Abundance of stromatoporoids, tabulate corals and algae suggest well aerated, highly agitated marine environment with normal salinity. Good intergranular and vuggy porosity is found throughout the reef.

Strontium content of the Leduc, determined by X-ray fluorescence method indicates a fore-reef location for the well. Strontium decreases with depth and intensity of recrystallization.

Well developed crystals of sphalerite in the Leduc Formation occur in vugs

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along with secondary calcite crystals. Chemical analysis reveals that the sphalerite was formed at low temperature. Presence of iron, cadmium and copper is detected by X-ray fluorescence technique.

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