Breccia is a lithological facies present in the McMurray Formation of the Athabasca oil sands of northeast Alberta. It consists of mud or shale clasts embedded in clean sands. The mud content of this facies varies from 0-100% and the clasts range in size from millimetres to metres with varying degree of angularity and sorting. Breccia is common in bitumen reservoirs. From an in-situ recovery perspective, breccia can alter fluid flow and reduce the overall oil saturation due to the presence of the mud clasts. To properly characterize the reservoir flow properties, it is necessary to develop a systematic procedure to assign the vertical and horizontal permeability of breccia zones on a scale that is suitable for the numerical simulation of recovery methods such as steam-assisted gravity drainage (SAGD).

A methodology to calculate the 2-D permeability of breccia facies from core photographs and mathematical theory has been described in a previous paper. However, core photographs do not capture the three dimensional nature of the mud clasts in the breccia. In this paper, the 2-D theory is extended to 3-D by treating the mud clasts as impermeable ellipsoids. The effective permeability of breccia regions may be calculated from the permeability of the sand in which the mud clasts are embedded if the size and orientations of the clasts are known. As for the 2-D case, the results from theory are in satisfactory agreement with those from flow simulation. Using the theory specialized to the case of oblate spheroidal clasts, a procedure is developed to estimate the 3-D permeability of breccia regions, based on 2-D information from core photographs. The paper concludes with guidelines for systematic permeability assignment in the breccia zones of the oil sands as well as other similar formations.

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