Modifications to Butler Theory for Geomechanical Effects at the Edge of SAGD Steam Chamber. Part I: Drained Condition

Abstract Steam-assisted gravity drainage (SAGD) has been demonstrated to be a successful thermal recovery technique for recovering bitumen from oil sand reservoirs where the viscosity of the bitumen is typically hundreds of thousands to millions of centipoise. High pressure and high temperature steam injection cause significant stress changes at the edge of the steam chamber including shear dilation which, in turn, can enhance the absolute permeability. The importance of considering geomechanical effects in SAGD process has been extensively discussed in the literature but geomechanical effects have been neglected in the classic SAGD analytical models. All analytical models are typically incapable of fully predicting actuall SAGD production rates without using a correction factor; this can be a result of neglecting geomechanical effects. In the research documented here, we examine geomechanical enhancement at the edge of steam chamber where the oil sand has been sheared under thermal stimulation. We describe a mechanism and evaluate the oil drainage parallel to the interface of steam chamber caused by permeability enhancement from thermal stresses. Finally, we present a modified Butler's Theory that includes geomechanical effects. The results are directly applicable to understanding the geomechanical effects on oil drainage flow at the edge of SAGD chamber.