In situ extraction of ultra viscous deposits from the vast bitumen resources in western Alberta requires significant water and energy usage which consequently lead to green house gas emissions. Currently proven steam-based recovery schemes include Cyclic Steam Stimulation, Steamflooding, and Steam Assisted Gravity Drainage (SAGD) processes, which are accompanied by many economical and environmental challenges. Co-injection of solvent with steam is a technology that has the potential to improve the efficiency of steam processes as well as reduce the energy use and CO2 emissions.

In recent years, researchers and industry have attempted to further develop the process by conducting fundamental research as well as field pilot trials with varying degrees of success. However, the current level of understanding of the process and knowledge around the fundamental physics and mechanisms involved are not fully satisfactory.

In this paper, a parametric simulation study was performed to address the key aspects of the solvent co-injection (SCI) process that contribute to further understanding and development of the process. Simulation observations were verified with experimental evidence where available to support the results and conclusions. Effects of several operational and geological parameters were evaluated on the performance of the SCI process and the relative performance benefits were assessed over normal SAGD operations. These parameters included solvent type, solvent concentration, initial solution gas-oil ratio, relative permeability curves, pay thickness, and presence of a low quality top layer.

The results revealed that the optimum solvent should not only be chosen on the basis of mobility improvement capability, but should also consider other operational, phase and flow behavioral and/or geological conditions that are set or present. Higher concentrations of solvents showed more energy saving upsides than rate acceleration benefits. It was also observed that the reservoir steam intake rate is still likely to be the prime performance indicator of the SCI process. In addition, it was found that the potential exists with the SCI process for accessing more resources, particularly below the producer level. Furthermore, steam trap control on the producer seems to be problematic when utilized for SCI simulation. With the current well control capacity of simulators, a higher degree of subcool is likely to be needed to avoid live vapor phase production from the producer.

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