Chapter 9: The Devonian Petroleum System of the Western Canada Sedimentary Basin — with Implications for Heavy-oil Reservoir Geology
Hans G. Machel, 2010. "The Devonian Petroleum System of the Western Canada Sedimentary Basin — with Implications for Heavy-oil Reservoir Geology", Heavy Oils: Reservoir Characterization and Production Monitoring, Satinder Chopra, Laurence R. Lines, Douglas R. Schmitt, Michael L. Batzle
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The Western Canada Sedimentary Basin is one of the most prolific and best researched petroliferous basins in the world. Hydrocarbons were first discovered in commercial quantities in the Mississippian Turner Valley field southwest of Calgary in 1914, but this field was relatively small and economically insignificant in the long run. The first prolific oil field was discovered in a Devonian reef in 1947 near the town of Leduc close to Edmonton. This discovery started an economic boom in the province of Alberta that is ongoing to this day, on the basis of oil and gas revenue. Although agriculture, forestry, and high-technology industries have considerably reduced the importance of petroleum revenue in the last 20 years, Alberta still derives approximately half (when oil prices are high, even more) of its gross domestic revenue from oil and gas.
Exploration spread to the neighboring provinces of Saskatchewan, Manitoba, and British Columbia in the 1950s and 1960s, when it became clear that oil and gas also occur in the eastern extensions of the Western Canada Sedimentary Basin. Today, after approximately 60 years of intensive exploration, during which very large petroleum resources were found also in various Mesozoic systems, Alberta remains the province with the most petroleum resources, although the emphasis has shifted from conventional to unconventional resources. Most commercial accumulations of hydrocarbons occur in two petroleum systems, the Devonian and the Cretaceous, with relatively minor accumulations in between (Figure 1). The Alberta Basin, which is the western part of the Western Canada Sedimentary Basin, contains approximately 8.2× 109 m3 ( 52× 109 billion barrels [bbls]) of conventional initial oil in place (IOP), compared with 1.8× 109 m3 ( 12× 109 bbls) conventional IOP in the Williston Basin, which is the eastern part of the Western Canada Sedimentary Basin (Figures 1–3). These conventional oil and gas resources, which have sustained the local economy and petroleum industry for approximately 50 years, are in rapid decline and now nearly exhausted (AEUB, 2007). Thus the unconventional resources are now of much greater importance, economically and geopolitically. The Alberta Basin hosts supergiant reserves of unconventional oil in Cretaceous sands and Devonian carbonates. The major three oil sand (also called tar sand) deposits alone (Athabasca, Cold Lake, Peace River) contain an estimated 267× 109 m3 of oil (Creaney et al., 1994; Hay, 1994; see Figure 1; AEUB Report ST98-2007 cites 270× 109 m3 , which is within the margin of error). In addition, the underlying carbonates (mainly the Upper Devonian Grosmont Formation) host at least an additional 50× 109 m3 of oil (Creaney et al., 1994; Hay, 1994; see Figure 1), whereas AEUB Report ST98-2007 and Alvarez (2008) cite up to 71× 109 m3 of oil in the carbonates. There obviously is a much larger margin of error in the estimates of the carbonates, and future resource evaluations may well push the estimates even higher.
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Heavy oil is an important global resource with reserves comparable to those of conventional oil. As conventional resources get thinner, attention is being focused on heavy oil and bitumen, which hold the promise of becoming useful fuels. Already more than 1 million barrels of oil are being produced from the oil sands in Canada; heavy oil represents half of California’s crude oil production in the United States and is a major production in Mexico. With demand for global energy soaring, heavy oil will undoubtedly be an important resource to be exploited in a big way in the near future.
The SEG Development and Production Committee held its Heavy Oil Forum in Edmonton, Alberta, in July 2007. This was a joint research forum cosponsored by the Canadian Society of Exploration Geophysicists (CSEG) and SEG and hosted by the University of Alberta. Preceding the forum, a field trip took the participants to the vast Athabasca Oil Sands region where they observed the outcrops, open pit mining, and steam injection operations, followed by a tour of the steam-assisted gravity drainage projects. Topics of the well-attended forum included the definition of heavy oil; where is heavy oil found; how it is produced; heavy-oil reservoir characterization; fluid and rock properties; electrical, tilt, and gravity techniques; borehole, surface seismic measurements; and microseismicity.