Co-injection of solvent and steam in Expanding Solvent-Steam Assisted Gravity Drainage (ES-SAGD) increases the mobility of highly viscous oil relative to conventional SAGD wherein only steam is injected. This consequently results in higher oil production rates and lower energy consumption relative to SAGD due to the combined benefits of heating and dilution. Current efforts have been made to study mass transfer from a single-component-solvent/steam mixture into the heavy oil at the steam front, while the low-cost multicomponent solvent is actually co-injected with steam on the field, which presents a much more complicated interfacial condition.

In this paper, a generalized methodology has been developed to couple heat and mass transfer of this solvents–steam–heavy oil system at the interface. In the model, the equation of state and fugacity equation are integrated to calculate and analysis the equilibrium state of transition interface. Then, the transition interface model is established based on heat transfer formulations and gaseous phase convective equations. Finally, under the temperature and velocity boundaries, the model is solved by applying implicit Runge-Kutta method and the results are used to analysis the heat and mass transfer characteristics.

The predicted results show that increasing the fraction of lighter solvent can enhance mass transfer, while the heat transferred is seriously deteriorated. Besides, the closer the bubble point temperature and dew point temperature of the stream is, the smaller the elevation of mass transfer will be, but the heat transfer is almost unaffected. Therefore, to realize the best effects of heat and mass transfer, solvents with larger saturation temperature difference should be applied, and the composition of the solvents should be carefully determined according to the formation properties and solvent components.

Conducting an ES-SAGD project on a field has many challenges, especially considering its main economic factors: production increase and solvent cost. With the new methodology, an optimum multicomponent solvent can be screened from the ocean of solvent candidates for a best heat and mass transfer performance in an ES-SAGD process and hence the oil flux at the chamber edge can be maximized with a minimized solvent cost. Therefore, it is of fundamental and practical importance to study the coupled heat and mass transfer of multicomponent solvents–steam–heavy oil system at the interface.

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