Over the past decade, Canada's heavy oil industry has experienced a remarkable resurgence, much of which has been technologically driven. High cash flows and the forecasts of ever increasing oil prices resulted in a high level of activity in heavy oil and oil sands development in Canada in the early 80's. Much of this activity was temporarily shelved with the oil price crash in the middle of the decade. A large resource base combined with limited prospects for new light oil discoveries were the driving forces for renewed development. However, level oil prices necessitated reduced development and operating costs. This has been achieved through a concerted application of technology.
Horizontal wells, progressive cavity pumps, foamy oil/sand production, cyclic steam stimulation and steam assisted gravity drainage (SAGD) in a number of forms have all played a part. Of these, the advent of low cost, precision drilled, horizontal wells has had the greatest impact. Improved primary production, particularly in areas with bottom water, enhanced cyclic steam stimulation, steam assisted gravity drainage and horizontal well steam drive are some of the new or enhanced recovery processes made possible with horizontal wells.
Field activity in Canada has now reached an unprecedented level with new commercial and experimental projects being initiated on a regular basis. This paper describes a number of the technological advances made possible by horizontal wells and illustrates them with descriptions of field projects.
Canada's heavy oil and oil sands resources are located in northeastern Alberta and western Saskatchewan (Fig. 1). This vast resource is estimated to contain more than 160 million cubic metres of oil in place. With the exception of the Carbonate Triangle, the majority of this heavy oil and bitumen is contained in Lower Cretaceous sand deposits of continental to marine shoreline origin. The sands are generally uncemented with high porosity and permeability. The oils range in gravity from 20 API to 8 API with viscosities from a few hundred to more than a million mPa.s. The reservoirs are shallow, at low pressure and temperature and the solution gas content is low. While the bitumen reservoirs can be thick (30+ metres) the heavy oil reservoirs are usually thin (5 to 10 metres), often with bottom water. Early attempts to produce these oils were restricted by the low flow rates resulting from high viscosity, water breakthrough and problems with sand production. Where production was possible, recoveries were usually limited to 3 to 5% of the oil in place. In recent years, technological advances in both primary and enhanced recovery have resulted in significant improvements in both the producibility and the level of recovery for heavy oils.
A technological advance that has had a major impact on the heavy oil industry is the ability to drill long, directionally controlled horizontal wells with per metre costs similar to those for vertical wells. Two principle advantages attributed to horizontal wells in primary heavy oil production are lower unit cost and the ability to effectively produce reservoirs with bottom water. Long (1000 – 1500 metre) horizontal wells can now be drilled for 3 to 4 times the cost of a vertical well but the increased exposure to the reservoir can yield 10 times the production rate. Thus the unit cost of production is reduced. The enlarged drainage volume, reduced impact of heterogeneities, reduced pressure drawdown and lower economic production rate all contribute to higher ultimate recover, again lowering the unit cost of production. Surface facility costs are also reduced as the wells themselves replace much of the gathering system associated with vertical wells and batteries can be consolidated, especially if a number of wells are drilled from a common location. P. 513^