Reservoir Geology Of The S.W. Midale Pool Southeast Saskatchewan

Schneberger, Keith M. (Saskatchewan Oil & Gas Corporation)


The Southwest Midale extension of the main Midale pool was discovered in 1956 by the exploratory well Trans Empire et al Halbrile 4-25-5-12W2M which obtained oil production from the N1ississippian Midale Beds. Delineation and development drilling from 1956 to 1985, resulted in a total of 42 wells, 31 of which were cased as potential Midale oil wells.

The Midale Marly member is responsible for approximately 75% of production from the thirty-one oilwells developed in the Southwest Mida1e pool. The remaining 25% is attributed to the Midale Vuggy and Frobisher Halbrite members. To date, this pool has produced in excess of 400,000m3 medium gravity crude oil on primary production.

Unique diagenetic events affecting the Marly and Vuggy reservoir lithofacies have either developed reservoir (i.e. Vuggy vadose zone solutioning, Marly dolomitization), or destroyed reservoir (i.e. Vuggy sparry calcite/anhydrite cementation, incomplete Marly dolomitization). The understanding of the depositional and diagenetic characteristics of the Midale Beds within the pool resulted in the following conclusions; (1) lateral continuity and relative homogeneity of the Marly dolomite reservoir facies (plus the general excellent quality and thickness of this reservoir in the areas of production) suggests that the Marly will be an excellent candidate for a waterflood scheme, (2) lateral discontinuity and heterogeneity of the Vuggy packstone/grainstone reservoir facies (in addition [Q general poorer quality reservoir development) suggests that the Vuggy will be prone to selective and limited waterflood applicable to localized areas, (3) negligible reservoir communication between the Marly and Vuggy members is anticipated, since the development of a laterally continuous and impermeable black, carbonaceous lime mudstone near the top of the Vuggy member acts as a vertical permeability barrier.

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