ABSTRACT: Evolution and Preservation of Microporosity in Middle-Upper Devonian Kee Scarp Formation, Norman Wells, N.W.T., Canada

AZMY, K., and I. AL-AASM, University of Windsor, Windsor, Ontario, Canada

The Middle-Upper Devonian Kee Scarp limestone at Norman Wells consists of a carbonate platform and an overlying reefal buildup. An episodic increase in the rate of sea-level rise produced multiple cycles of reef growth, with backstepping characters. Reservoir porosity of these reefs is mostly represented by micropores of various types developed during diagenesis by action of aggrading neomorphism and dissolution. The microporosity was developed as intercrystalline microvoids within the present LMC stromatoporoids, algae, and matrix components. SEM studies show that microporisity development responded to neomorphism at various rates. This may reflect the difference in original architectural buildup as well as original mineralogy of skeletal components. Stromatoporoids have fairly well eveloped microporosity in most facies. Variations in types of micropores have been noticed between and within different facies. Reef margins; grain shoals; and lower, middle, and upper foreslope facies have the highest and best developed microporosity compared with lagoon, reef flat, and tidal fleet facies.

The micropores in Kee Scarp limestone can be classified into four categories based on their shapes: (1) stepwise rhombic, about 1 um to 2 um in diameter; mainly developed in stromatoporoids; (2) intercrystalline rhombic, about 1 um in diameter; mainly in algal aggregates; (3) microvugs, 4 um to 8 um in diameter; mainly in algal aggregates; and (4) microchannels, 2 um length and 0.5 um width; in algal aggregates and stromatoporoids. The stepwise rhombic and microvugs are developed mainly at the Kee Scarp reef exterior and constitute the best type of reservoir porosity.

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