Analytical and numerical study of thermal and solvent-based gravity drainage for heavy oil recovery

Abstract With the increasing demand for energy, an initial screening for heavy oil recovery options is important. However, the calculation of the gravity drainage recovery of heavy oil is complex and involves coupled fields and changes in the properties of heavy oil or its mixtures. There is currently no general analytical treatment for heavy oil gravity drainage processes, such as steam-assisted gravity drainage (SAGD), vapor extraction (VAPEX) and warm VAPEX, with the simplest possible assumptions but with the necessary mechanisms. In this study, a novel discrete hypothetical model has been proposed to simplify the calculation of gravity drainage flow in porous media. Then, a validated equation with a reasonable mixing rule is used to describe the property changes of heavy oil or its mixtures under decoupled temperature and concentration variables. Finally, internal velocity distributions for different gravity drainage processes are validated with numerical modeling results. Our results agree with previous work on the importance of mass transfer coefficients. Moreover, different from the previous work, the effect of slightly water-soluble solvents (dimethyl ether) has been investigated on diffusion in both the oil phase and the water phase. For solvent-based heavy oil recovery, a slightly water-soluble solvent shows great advantages with promising application potentials. The results of this study can guide the initial screening for a gravity drainage process and the analysis of its key mechanisms.