In Alberta, Canada, over 80% of oil sand reserves are suitable for thermal in-situ processes such as the steam assisted gravity drainage (SAGD) process. SAGD recovery is contingent on reducing the viscosity of bitumen, which is immobile at reservoir temperature, to increase its mobility, thus increasing recovery efficiency. Processes based on the co-injection of solvent and steam targeting further reduction of bitumen viscosity have been extensively investigated. These studies generally ignore the potential role of bitumen-water interfacial tension on bitumen mobility and bitumen recovery.
In this study, we propose a new analytical model approach to analyze flow characteristics of injected steam in a bitumen containing reservoir and to clarify the physics of the displacement process during SAGD. The thickness of the chamber front where viscosity reduction occurs is defined for different injection and reservoir conditions and flow patterns are created for different fluid (viscosity and interfacial tension) and reservoir properties (thickness). This model shows how bitumen-water interfacial tension affects bitumen mobility and thereby influences both SAGD displacement efficiency and ultimate bitumen recovery. A composite set of models including the effects of interfacial tension between the bitumen and water in addition to viscosity reduction are developed.
Finally, the observations obtained through analytical model studies are compared against SAGD field observations accumulated over the last two decades. The focus of this comparison is on the advancement rate of the chamber front and its growth characteristics. By understanding the bitumen to water interfacial tension effects, it will be possible to make a better prediction of the relative benefits of solvent or surfactant to accelerate the recovery rate and improve ultimate recovery.