SAGD Comes of AGE!

Abstract

Abstract Canada's remaining resources of conventional crude oil are relatively slight and dwindling, but heavy oil and, particularly, bitumen resources are large. Their quantity approaches that of the resources of conventional oil in the Middle East. Without bitumen and heavy oil, Canada would face a growing requirement for funds to purchase foreign oil. This is already a severe problem for the United States whose large, unfavourable balance of trade stems from its need to import much of its crude oil. Canada's success in producing bitumen by open pit mining of shallow Athabasca deposits by Suncor and Syncrude and by cyclic steaming at Cold Lake by Imperial Oil has already had a significant impact. However, although these approaches are economic, both have serious limitations. Open pit mining is limited to shallow deposits and less than 10% of the total Athabasca resource is suitable. Also, open pit mining requires the disruption of the landscape and the handling of tonnages of tailings at least ten times greater than those of the produced bitumen. The disposal of the high clay content, "middling" stream from the hot water separation process which settles at a notoriously slow rate(1) and accumulates in tailings ponds that require prodigious areas is a severe environmental problem. Imperial Oil's cyclic steaming has considerable environmental advantages since the reservoir solids are left in place. However, it is not a gentle process; the periodic injection of steam at pressures up to 14 MPa (2000 psi) sometimes results in well failure from the large cyclic, thermal, well-stresses. An important limitation of the process is that the recovery of the oil in place is only about 25%. Practical recovery processes for further recovery have not been defined(2). The consumption of fresh water equal in volume to the produced oil places a demand on the environment. SAGD gives a higher recovery and requires less water, less energy and fewer wells. Operation of the process is simpler than cyclic steaming because it is continuous and because of the fewer wells. Efficient recovery of heat from the produced fluids is possible and, because steam is required at a lower pressure, the cogeneration of electric power is more economic. The SAGD Concept Steam Assisted Gravity Drainage Process (SAGD) was introduced by the author and his former colleagues at Imperial Oil in the late 1970s(3, 4, 5). It was developed as a more systematic technique for the recovery of bitumen. The concept, shown in Figure 1, is now widely understood and is described in detail elsewhere(6, 7, 8). It was predicted, from theory, and from scaled model experiments, that production rates of the order of several hundred to over a thousand B/day could be expected from well pairs about 500 m long; this has since been confirmed by the operation of full scale pilots-in Athabasca, in Cold Lake, in Peace River and in Lloydminster. Essential Features of SAGD Since gravity does not provide an adequate drive to move heated bitumens to a conventional well at an economic rate(9) horizontal production wells are used for SAGD.