Chapter 15: Geostatistical Reservoir Modeling Focusing on the Effect of Mudstone Clasts on Permeability for the Steam-assisted Gravity Drainage Process in the Athabasca Oil Sands
Koji Kashihara, Akihisa Takahashi, Takashi Tsuji, Takahiro Torigoe, Koji Hosokoshi, Kenji Endo, 2010. "Geostatistical Reservoir Modeling Focusing on the Effect of Mudstone Clasts on Permeability for the Steam-assisted Gravity Drainage Process in the Athabasca Oil Sands", Heavy Oils: Reservoir Characterization and Production Monitoring, Satinder Chopra, Laurence R. Lines, Douglas R. Schmitt, Michael L. Batzle
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Steam-assisted gravity drainage (SAGD) method is a heavy-oil in situ recovery technique used for bitumen production of the Athabasca Oil Sands, where bitumen reserves from oil sands are estimated at 173 billion barrels (Alberta Energy and Utilities Board, 2008). The typical configuration of the SAGD includes two horizontal wells of 750 m in length and vertically separated by 5 m, in which the upper well is used for steam injection to increase the mobility of the bitumen and the lower well is for bitumen production. Feasible bitumen recovery from oil sands by SAGD is limited within the lateral perpendicular distance of approximately 50 m from the horizontal well pairs. Therefore, profitably viable bitumen production performance requires that the SAGD well pair location be at thick reservoir sands. The complexity of facies distribution in the target formation requires effort in understanding detailed distribution of the reservoir sands. A deterministically constructed geologic model was visualized to better understand 3D distribution of the reservoir sands in the study area (Takahashi et al., 2006). Because lateral continuity of the lithologic facies in the area of interest is shorter than typical interwell distance, the deterministically predicted facies distribution leaves inherent uncertainty in terms of the bitumen production forecasting.
The reservoir sand facies can contain impermeable thin mudstone layers and impermeable mudstone clasts. Previous works including Schmitt (2004) and Takahashi et al. (2006) often refer to the thin mudstone layers adversely affecting the growth of the steam chamber during the SAGD process and consequent bitumen production performance. Although the mudstone clasts have not been often discussed in regard to the impact on the bitumen production performance, our field operation has experienced unexpectedly lowered bitumen production from the reservoir containing the mudstone clasts.
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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.