Heat and mass transfer characteristics of superheated fluid for hybrid solvent-steam process in perforated horizontal wellbores

In this paper, the authors presented a novel model for estimating thermophysical properties of solvent in perforated horizontal wellbores (PHWs) considering the complex heat and mass transfer characteristics in the PHWs, so that the phase state of the fluid in hybrid solvent-steam process can be predicted. Firstly, governing equations for mass flow and pressure drop were established based on mass and momentum balance principles and the Equation of State. More importantly, implicit equations for phase changes from superheated steam and solvent to wet steam and superheated solvent, and to wet steam and solvent, were derived based on heat and mass transfer in the wellbore. Next, the mathematical model was solved using Levenberg-Marquardt Algorithm (LMA). Finally, validation and sensitivity analysis of the model were conducted sequentially. The validated results showed that, when injecting heavier solvent in the hybrid process, the temperature along the PHWs tends to stay at a high level and the solvent condenses at position far away from the toe position of the wellbore, but that of lighter solvent injection shows an opposite trend. Furthermore, to increase the temperature at toe position of the PHWs when injecting lighter solvent in the hybrid process, a higher superheat degree at the heel of PHWs is preferred, while the increased superheat degree may not help to ease condensing of heavier solvent in the PHWs. Besides, increasing the injection rate is more beneficial to reducing the solvent loss along the horizontal wellbore for both heavy and light solvent injection, than that of increasing the superheat degree at the wellbore head. (C) 2018 Elsevier Ltd. All rights reserved.