Leduc, A New Life At 38

Abstract

Abstract Discovery of oil in well Imperial Leduc No.2 on May 10, 1947, marked not only a long-awaited success for Imperial Oil Limited in western Canada, but also provided a major impetus for the subsequent explosive growth of the Alberta petroleum industry. Unique among its Devonian neighbours on the active Cooking Lake Aquifer, the Leduc D-3A Pool had a thin, areally-extensive oil leg, and a large gas cap. Balancing the thinning oil zone between the gas cap and aquifer has been an unrelenting challenge of reservoir management. Reducing the oil zone from its original 11.6 metres to 1.5 metres has been a 37-year success story. However, the operator is about to lose the upper hand. Two years of appraisal and planning have focussed on the future of the remaining hydrocarbon reserve. This paper summarizes the past and present of the Leduc pool, and looks futuristically toward the day of final depletion. Introduction The Leduc D-3A Pool is located 20 kilometres southwest of Edmonton (Fig. 1). Discovered in May 1947, It is one of a series of reef structures located on the Rimbey-Meadowbrook geologic trend which extends some 480 kilometres in a southwest-northeast direction across central Alberta. Leduc is located on the southern portion of the trend, which also includes the major hydrocarbon-bearing pools of Homeglen Rimbey. Westerose South, Westerose, Bonnie Glen, Wizard Lake, Glen Park, Acheson, Big Lake and St. Albert (Fig. 2). All pools receive strong pressure support from the Cooking Lake Aquifer. Based on geological data, the Leduc D-3A Pool is divided into three distinct areas (Fig. 3):the Main Pool, the focus of this paper;the Saddle Area; andthe Southeast Extension The three areas of the Leduc D-3A Pool originally contained die hydrocarbon accumulations shown in Table 1. Since discovery, 63 per cent of the 50.4 × 106m3 of original oil-in-place, or 98 per cent of estimated reserves have been recovered from the Main Pool. At present, it is estimated that a thin 1.5 metre oil leg remains. While the challenge of managing oil production from a thin oil sandwich has been successful, the continually diminishing oil zone and near-depletion of reserves necessitates planning and executing the next phase of Main Pool depletion-a rapid gas cap production, commonly referred to as a blowdown. This paper familiarizes the reader with the past and present of the Leduc D-3A Pool, and provides forward-looking insight into the reservoir at times referred to as the genesis of the Canadian oil industry. Reservoir Geology General The Leduc D-3A Pool is one of the many Devonian reefs (Fig.2) enclosed in basinal shales of the Ireton and Duvernay Formations that grew upon the extensive Cooking Lake carbonate platform (Fig. 4). Fluids derived from compaction of the adjacent basinal sediments are thought to be the source of the dolomitization of all the bioherms or pools along the chain, as well as the western margin of the Cooking Lake platform.