Theoretical and physical modeling of a solvent vapour extraction (VAPEX) process for heavy oil recovery

Solvent vapour extraction (VAPEX) is an effective heavy oil recovery process because of its significant viscosity reduction through sufficient solvent dissolution and possible asphaltene precipitation. In this paper, an analytical model is developed to predict the accumulative heavy oil production in the entire VAPEX process. In the experiment, a total of five VAPEX tests are conducted to recover a heavy oil sample from a visual rectangular sand-packed high-pressure physical model and measure the accumulative heavy oil production versus time data. Theoretically, a mathematical model is formulated to predict the accumulative heavy oil production data at different times. It is assumed that the transition zone between the solvent chamber and the untouched heavy oil zone has two straight-line boundaries with a constant thickness during the VAPEX process. The constant transition-zone thickness is used as an adjustable parameter and thus determined by finding the best fit of the theoretically predicted accumulative heavy oil production data to the experimentally measured data. It is found that the maximum variation of the transition-zone thicknesses determined by using the accumulative heavy oil production data at different times is within 15% for the five VAPEX tests. This fact indicates that the constant transition-zone thickness assumption is acceptable. In addition, it is also found that in general, the transition-zone thickness is increased when the permeability of the VAPEX physical model is decreased. Moreover, the analytical model is applied to predict the position of the solvent chamber, and its horizontal spreading velocity and falling velocity. Both the horizontal spreading velocity and the falling velocity of the solvent chamber decrease with time as the VAPEX process proceeds.