Development and Application of Pseudo-Functions for Reservoir Simulation To Represent Shear Failure During the Cyclic Steam Process

Abstract

Abstract The steam stimulation process is a proven, commercially viable recovery process in oil sand reservoirs. However, uncertainties remain in the analysis of the recovery mechanism of the process. One of the important aspects is the nature of shear failure created by pore pressure increase in the reservoir during steam injection. The changes in mass and heat transport proper-ties in the heterogeneously deformed failure zone have been shown to be major factors affecting the recovery mechanism. This paper describes the theoretical and practical aspects of representing the shear failure zone in reservoir simulation, by means of pseudo relative permeability functions. Relative permeability hysteresis is commonly used in the simulation of the steam stimulation process. The paper gives the theory for the pseudo relative permeabilities caused by heterogeneously failed media. The new functions are derived by considering the shear failure phenomenon and have a characteristic similar to relative permeability hysteresis. A set of stress dependent pseudo relative permeabilities is proposed and a practical method for the use of the pseudo functions (including hysteresis) in a reservoir simulator is given. The pseudo relative permeability model is applied in the simulation of a well in the Esso Cold Lake site and shows that the hysteresis should be stress-dependent rather than saturation-dependent. Introduction A commonly used technique in simulating a cyclic steam stimulation process is the use of a relative permeability to water that is higher during the injection period than during the production period. The use of this technique is reported in a number of papers A similar hysteresis phenomenon of relative permeability to water has been presented which was derived from the laboratory studies. A brief summary of these papers is given by Ito et al. On the other hand, the influence of geomechanical properties of tar sand on reservoir engineering properties, such as change in porosity, absolute permeability and relative permeability has been receiving increased attention recently. Ito was the first to introduce the geomechanics into a reservoir simulator and named it the Sand Deformation Concept. In order to model the Sand Deformation Concept, a larger krw than the original value is used in the area where the pressure is high enough to deform the sand. Dietrich used the hysteresis of krw in a history match of a cyclic steam stimulation process. P. 225^