Chapter 3: Modeling Studies of Heavy Oil — In Between Solid and Fluid Properties
Agnibha Das, Mike Batzle, 2010. "Modeling Studies of Heavy Oil — In Between Solid and Fluid Properties", Heavy Oils: Reservoir Characterization and Production Monitoring, Satinder Chopra, Laurence R. Lines, Douglas R. Schmitt, Michael L. Batzle
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Rocks filled with heavy oil do not comply with established theories for porous media. Heavy oils demonstrate a blend of purely viscous and purely elastic properties, also referred to as viscoelasticity. They have a nonnegligible shear modulus that allows them to support shear-wave propagation depending on frequency and temperature. These oils behave as solids at high frequencies and low temperatures and as fluids at low frequencies and high temperatures. The solid-like properties of heavy oils violate Gassmann’s equation, the most common and widely used fluid-substitution technique in the industry.
Few instances of elastic property modeling for heavy-oil-saturated rocks have been reported. Most previously reported work has involved modeling without comparison with measured data, or modeled results on simple grain-fluid aggregates with comparison to measured ultrasonic data. We have modeled the viscoelastic properties of heavy-oil-saturated rock samples using the Hashin—Shtrikman (HS) bounds and the frequency-dependent complex shear modulus of the heavy oil. The two studied rock samples are very different in terms of lithology and consolidation state. In our exercise, we have extended the HS bounds to incorporate complexities such as intragranular porosity and the contribution of heavy oil to rock matrix properties. By considering the complex shear modulus of the heavy oil in our HS calculations, we have been able to estimate attenuation. We also tested the applicability of Ciz and Shapiro’s (2007) form of the generalized Gassmann’s equations in predicting the saturated bulk and shear moduli of the heavy-oil-saturated rock samples.
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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.