Chapter 12: Imaging Oil-sands Reservoir Heterogeneities Using Wide-angle Prestack Seismic Inversion
Baishali Roy, Phil Anno, Michael Gurch, 2010. "Imaging Oil-sands Reservoir Heterogeneities Using Wide-angle Prestack Seismic Inversion", Heavy Oils: Reservoir Characterization and Production Monitoring, Satinder Chopra, Laurence R. Lines, Douglas R. Schmitt, Michael L. Batzle
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Mass density, because of its linear relationship with porosity, has long been recognized as a potential seismic indicator of fluid saturation. Given its dependence on mineral composition, density can also be diagnostic for lithology. In this chapter, we discuss some key aspects of a wide-angle processing and density inversion workflow and apply it to a bitumen reservoir in Canada for imaging reservoir heterogeneities (e.g., shales) that can potentially act as permeability baffles. In this field, intrareservoir shales typically have higher densities than surrounding reservoir sands. This wide-angle workflow yields stable density estimates, from reflected P-waves alone, at a resolution suitable for mapping the intrareservoir shales.
This study is based on data from the Surmont bitumen reservoir approximately 60 km southeast of Fort McMurray, Alberta, Canada, in the Lower Cretaceous McMurray formation. The oil is too deep (400 m) to mine. Steam-assisted gravity drainage (SAGD) technology is being used to inject steam into the reservoir and heat the oil so that it can be produced. Shale heterogeneities within the reservoir (Figure 1) thicker than 3 m could have an impact on steam chamber development and affect SAGD performance. Predicting the areal extent and the thickness of these bodies would lead to better reservoir management.
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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.