Stratigraphy and reservoir properties, Devonian Kee Scarp Formation, Norman Wells, Northwest Territories

Abstract

The Kee Scarp Formation in the subsurface at Norman Wells, Northwest Territories, forms an elongate, northeast trending, flat-topped mound. Oil is produced on the up-dip northeast edge. The formation consists of two distinct members; a lower, argillaceous, bedded coralline limestone referred to as the platform member and an overlying, massive member of variable facies referred to as the reef complex. Cores were examined from the Norman Wells oil field, underlying the Mackenzie River, and from outcrops a few miles to the northeast. Reconstructions suggest that the oil field cores are from one atoll-like structure and the outcrop carbonates from another. These structures may have been moditied by pre-Canol erosion. Stromatoporoids are the most abundant fossils found in the Kee Scarp reef complex, and were the principal reef builders. The shape and size of the coenostea are useful in making environmental interpretations, since individuals commonly assume a variety of environmentallycontrolled shapes. The petrographic and palaeontologie characteristics of the sediments are used to define six major facies within the Kee Scarp. These are the Amphipora packstone facies, the massive stromatoporoid grainstone facies, the stromatoporoid packstone facies, the fine pellet packstone facies, the dendroid stromatoporoid packstone facies, and the coral packstone facies. Division of the Kee Scarp reef complex into fore-reef, organic reef and back-reef zones is based on the environmental interpretation of the six main facies. In general, the fore-reef zone is characterized by the stromatoporoid packstone and fine pellet packstone facies, the organic reef by the massive stromatoporoid grainstone facies, and the back-reef zone by the fine pellet packstone and Amphipora packstone facies. Three pore types are recognized in the Kee Scarp; interparticle pores (mainly interpelletal), pores associated with stylolites, and pores associated with spar cement. Interparticle matrix pores are quantitatively the most important pore type. Reservoir properties were determined using an air displacement porometer and a mercury injection apparatus. They are most favorable in the fine pellet packstone and stromatoporoid packstone facies. In these facies, the average porosity is 20 per cent, the average permeability is 2 millidarcies, and the average pore size is 0.1 millimeters in diameter. Porosities and permeabilities are better in the subsurface than in the outcrop, for comparable lithologies. At best, the reservoir properties of the Kee Scarp are only fair when compared to the reservoir properties of other western Canada Devonian reservoirs. Note:This thesis contains maps that have been sized to fit the viewing area. Use the zoom in tool to view the maps in detail or to enlarge the text.