--> ABSTRACT: Sedimentology, Diagenesis and Dolomitization of the Nisku Formation (Upper Devonian, Frasnian) at Joffre Field, Alberta, Canada, by Abdul Al-Bastaki, John D. Humphrey, Clyde H. Moore, John Arestad; #91020 (1995).

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Sedimentology, Diagenesis and Dolomitization of the Nisku Formation (Upper Devonian, Frasnian) at Joffre Field, Alberta, Canada

Abdul Al-Bastaki, John D. Humphrey, Clyde H. Moore, John Arestad

The dolomitized Nisku Formation (Upper Devonian, Frasnian) is a prolific petroleum producer in the Western Canada Sedimentary Basin. The field is located in the inner Nisku Shelf region of south-central Alberta, between Calgary and Edmonton, overlying the Bashaw complex of Leduc age. Hydrocarbons in the field are primarily produced from the Nisku. Estimated recovery from the field is 63.7 million bbl and it has thus far produced about 47 million bbl of oil. The focus of the study includes understanding reservoir heterogeneity, diagenesis/dolomitization, porosity evolution, and anhydrite plugging which forms the updip trap in Joffre Field.

Several cores of the Nisku Formation from Joffre Field and nearby outlying areas were examined in this study. The Nisku facies in the study area is composed of tabular stromatoporoid and coral build-up facies overlying the Ireton Shale. Flooding of the stromatoporoid/coral facies resulted in deposition of a deeper-water Amphipora rudstone/floatstone facies which, in turn, is overlain by packstone/grainstone facies. The formation then shallows upward into an arid tidal flat sequence, characterized by desiccation features and rip-up clasts, which is succeeded by hypersaline facies containing laminated anhydrite, micrite, and minor clay-rich siliciclastics.

The Nisku Formation at Joffre Field is pervasively dolomitized. Early, widespread peritidal-associated dolomite occurs as replacement of matrix and grains. Reef-matrix dolomitization likely occurred relatively early, under shallow burial conditions. Dolomite cements occur as euhedral, CL-zoned crystals filling primary and secondary pores. Dolomite neomorphism is indicated by crystal margin luminescence associated with fluid pathways. Anhydrite plugging of much of the available pore space compromises reservoir quality and is the key to understanding the destruction of favorable reservoir properties at Joffre Field.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995