--> ABSTRACT: Geologic Model of the Middle-Upper Devonian Snipe Lake BHL 'A' Pool Platform-Reef Complex, Western Canada, by I. D. Muir, G. L. Springate, J. R. Mawdsley; #91003 (1990).

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ABSTRACT: Geologic Model of the Middle-Upper Devonian Snipe Lake BHL 'A' Pool Platform-Reef Complex, Western Canada

I. D. Muir, G. L. Springate, J. R. Mawdsley

The Snipe Lake BHL 'A' pool reef is one of a number of large Swan Hills atoll reef complexes of Late Devonian age in central Alberta. This study has developed a model for predicting the distribution of reservoir facies in the Snipe Lake 'A' pool. The reservoir description is an integral component for tailoring an appropriate depletion plan.

Variations in reservoir quality are due primarily to depositional attributes. Reservoir facies include reef flat/shoal margin, reef

margin/upper foreslope, middle foreslope, and allochthonous foreslope facies. Parts of the grainy lagoon may also be effective reservoir, although vertical permeability tends to be much reduced compared to other reservoir facies. Reef/shoal margin configuration will also affect reservoir quality and continuity. Muddy margin facies are mainly confined to reentrants and may behave as low-permeability barriers to structurally downdip flank water injectors.

A chronostratigraphic framework using cycle correlation in the Snipe Lake platform-reef reservoir helped determine facies-controlled reservoir continuity and distribution of low-permeability facies. The platform (53 m thick) consists of five major cycles (A1-5) arranged in a backstepping stacking pattern. Reservoir facies are confined to the uppermost three platform cycles within the pool unit boundary. The Snipe Lake reef complex initiated on the A5 accretionary platform high and comprises four major cycles (BO-2, C) within the unit. The BO cycle contains in excess of 60% of the Snipe Lake recoverable reserves. This lowermost reef cycle is characterized by progradational margins and expanded reservoir facies, presumably due to a combination of prolonged relative stillstand and subdue shallow bathymetry. Other platform-reef cycles are typified by aggradational margins and narrower reservoir facies belts.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990