Abstract

For oil sands assets having bitumen resources located near the ground surface, geomechanical assessments of caprock performance during steam-assisted gravity drainage (SAGD) operations have become increasingly important. These assessments need to determine and demonstrate whether the caprock can effectively withstand the induced stress and strain loadings from the SAGD operation throughout the life of the development.

The importance of caprock integrity for SAGD developments was realized following the loss of caprock containment at the Total E&P Canada Ltd., Joslyn Creek SAGD project in 2006. In light of this failure, the Alberta Energy Resources Conservation Board (ERCB) stipulated a series of response activities to address caprock integrity, including the requirement that pilot and commercial SAGD projects in Alberta need to conduct a geomechanical assessment of caprock integrity as part of the application process.

The authors completed a geomechanical simulation study of the Clearwater Formation caprock performance at a proposed, shallow, low pressure, SAGD (LP-SAGD) pilot project located southeast of Fort McMurray, Alberta, Canada. For this investigation, a 3D, coupled, reservoir and geomechanical simulation was conducted forecasting 10 years of asset response to the maximum operating pressure of 1,000 kPaa. The geomechanical response of the caprock to temperature changes, increased pore pressure and the induced stress and strain fields from the steam chamber was simulated as part of the caprock integrity assessment for the pilot project.

This paper presents the results of this simulation study and the uncertainties and risks associated with evaluating caprock containment of SAGD operations using numerical methods. The results of key geomechanical parameters, such as minimum principal effective stress, shear stress level, factor of safety and surface displacement are presented. A summary of the post-failure analyses of caprock containment at the Joslyn Creek SAGD project is presented.

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