Abstract

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.

Introduction

The Southwest Midale pool in S.E. Saskatchewan, located approximately 4 miles west of the town of Midale, is a southern extension from the main Midale Field (Figure 1). The Southwest Midale pool, as defined by the Saskatchewan Oil and Gas Corporation, encompasses Section 30-5-11W2M. Sections 14–16, 22–25, and portions of Sections 35 & 36-512W2M. The majority of oil production is from the Mississippian Midale Beds (Charles Formation) with additional production obtained from the Mississippian Frobisher Beds (Mission Canyon Formation).

The Southwest Midale pool was discovered in August, 1956 with the drilling and casing of the exploratory well Trans Empire et al Halbrite 4-15-S-11W1M. To date, this oilwell has produced 31,l00m3 oil, 21,700 m3 water in 10,290 days from the Midale Beds. Subsequent delineation and development drilling oil an 80 acre (32 ha) drainage pattern resulted in a total of 42 wells, thirty-one of which were cased for oil production. As of December 1988, this pool has produced 491,000 m3 of medium gravity crude oil on primary production.

Successful commercial waterflood schemes were implemented in the early 1960's by Shell Canada in the Midale Field and PanCanadian in the Weybum Field (Figure I). The Southwest Midale pool is considered an excellent candidate for a similar secondary recovery scheme, providing similar geological and reservoir conditions exist.

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