Abstract

Two stratigraphic intervals in Western Saskatchewan, in widely separated areas, contain the largest proportion of the heavy oil shows. The Upper Devonian Birdbear Formation has numerous shows in the Kindersley area and the Mississippian Madison Formation of the southwest has been penetrated by 14 wells that have heavy oil occurrences in core or drill steam tests. Limited oil production has been obtained from both stratigraphic intervals.

The Birdbear shows are in thin streaks of rhombic dolomite and in partially calcite-cemented vugs in a thinly bedded, dominantly, microcrystalline dolomite. Madison shows are found in dolomitized and recrystallized skeletal wackestones and crinoidal packs tones and grainstones. The dolomitization has affected rocks within the upper 10-15 metres immediately beneath the sub-Mesozoic unconformity and appears to occur mainly on paleo topographic positive features.

Mercury injection capillary pressure analyses permit the separation of the Madison rocks into two good reservoir and two poor or non-reservoir types and can be used to assist in the determination of the volume of oil-in-place in the Madison Formation. Three potentially good producing localities appear to exist in the Madison in the south Cypress Hills area. They have a combined estimated oil-in-place between 30 × 106 and 40 × 106 cubic metres.

Introduction

The mid-Paleozoic rocks of western Saskatchewan are part of a continuum of Mississippian and Devonian strata draped over the Sweetgrass Arch of eastern Alberta. These rocks have been known to be oil-bearing since the early days of exploration on the Arch, but most of the shows were disregarde

d due to the low API gravity of the oil. Stratigraphic testing of the Devonian in western Saskatchewan began in the late 1940's, but the majority of wells penetrating those rocks were drilled in the 1950' sand 1960' s. Several oil shows 'Were encountered in Devonian strata during that time. Most of these were found in wells located in the area between townships 26 and 40 and range 13 west of the third meridian and the Alberta-Saskatchewan interprovincial boundary. The Upper Devonian rocks of the Duperow and Birdbear Formations contained the bulk of these shows, which were recognized in both drillstem test results and cores. The oil was a heavy tarry variety and little interest was shown in attempting to determine potential economic yield until 1968 when Husky Oil attempted to obtain commercial production from Husky INC N. Hoosier 10–28 (Lsd lO-28-32-28W3) and INC Husky Southcourt 6–3 (Lsd 0-]-])-28W3). Neither well yielded large volumes of oil and they were abandoned after short production periods.

Exploration drilling in Mississippian rocks in western Saskatchewan in the early to late 1950's identified several heavy oil shows. The most significant was the Coop et al. Battle Creek 1-27 well. (Lsd 1-27-3-26W3), which recovered 1262m of ad with a density of: 997kg/cm2 (11 degrees API) in a drillstem test immediately beneath the sub-Mesozoic unconformity, within the Mississippian Madison Formation.

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