Abstract

Starting in the 1970s, Union Oil Company of Canada (Unocal), in partnership with Canadian Superior and the Alberta Government, conducted a series of exploratory field tests in the bitumen-saturated carbonate rocks of the Grosmont Formation. These tests applied thermal recovery technologies, including steam drive and cyclic steam stimulation (CSS), that were in their early stages of development. Significant amounts of production and observational data were obtained. Although some results were encouraging, activities in Grosmont were eventually stalled in the mid 1980s as economic attention was shifted to Cold Lake and Athabasca Cretaceous siliclastic reservoirs. Since then, in situ bitumen recovery, 3D seismic, horizontal well and surface processing technologies have matured significantly. In light of the enormous resources (406 billion barrels) hosted within the Grosmont Formation, it is pertinent to ask whether those new technologies are applicable for carbonate reservoir development.

To answer this question, we studied data from the Unocal pilots conducted in the Grosmont C and augmented it with recent laboratory tests on newly acquired Grosmont C cores. The previous pilot CSS results were encouraging, with the cycle steam-to oil ratio as low as 3.65 and a peak rate of 440 bbls/d from a single vertical well. With subsequent cycles the ratio of the produced fluid to the injected fluid increased, signifying the injected energy was retained and more effective in later cycles. The operation strategy of the Unocal pilots and its implementation were not optimal and we believe that this could be improved with modern techniques.

Based on our new understanding of the Grosmont Formation and specifically the Grosmont C, a numerical model was created and verified with production data. Model results indicate that the application of SAGD will be a commercially viable recovery process for Grosmont carbonate reservoirs and that low pressure injection (below 3500kPa) would be desirable. The laboratory tests not only support these conclusions but also suggest that performance of the applicable thermal processes can be enhanced with the addition of solvent. A SAGD/solvent pilot test is planned to start up in late 2010. This pilot will be critical to the development of exploitation strategies applicable to Grosmont carbonate bitumen resources.

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