ABSTRACT:

Producing bitumen from oil sands reservoirs by steam injection will increase reservoir pressure that can change stress states and induce deformations in the reservoir and its surrounding formations, in particular the caprock overlying the reservoir. Caprock failure may lead to steam release to the overlying aquifers or to surface, that can cause significant economical, environmental, and safety impacts on field production operations. We developed a coupled model for evaluating caprock stability in the SAGD process by integrating a geomechanical model and a thermal reservoir simulator. The developed model was validated by predicting surface heave data measured from interferometric synthetic aperture radar (InSAR) images. The validated model was employed to evaluate caprock stability over a wide range of geological and geometric descriptions and steam injection conditions for SAGD field productions. For cases evaluated, safety factors were calculated to quantify the potential caprock instability induced by tensile or shear failure mechanism during steam injection. The possible ranges of safety factors are predicted by the model under various steam injection conditions.

1. INTRODUCTION

The steam assisted gravity drainage (SAGD) process is a widely applied thermal recovery technology for producing bitumen from oil sands reservoirs in Canada. In the SAGD process, steam injection plays a critical role on reducing the viscosity of bitumen which allows it to flow into the production well. However, during steam injection increasing reservoir pressure will change stress states and induce deformations in the reservoir and its surrounding formations, in particular the caprock overlying the reservoir. Caprock failure may lead to steam release to the overlying aquifers or to surface, that can cause significant economical, environmental, and safety impacts on field production operations. The risk of potential caprock failure is particularly high for shallow oil sands reservoirs with depth less than 350 meters under the typical SAGD operation.

This content is only available via PDF.
You can access this article if you purchase or spend a download.