Warm VAPEX: A Thermally Improved Vapor Extraction Process for Recovery of Heavy Oil and Bitumen

Abstract

In this paper, the warm vapor extraction process (VAPEX) is introduced for the recovery of heavy oil and bitumen as a variation of the conventional vapor extraction process by superheating the solvent vapor. The effect of the level of solvent superheat on the performance of the warm VAPEX process was investigated by varying the different experimental factors such as solvent temperature, oil viscosity, and permeability of the porous medium. The experiments were conducted with both Cold Lake bitumen and Lloydminster heavy oil at three levels of solvent vapor temperature (36, 43, and 50 °C) and two permeability levels (220 and 830 darcy). Normal pentane was used as the hydrocarbon solvent for the recovery of both the heavy oil and the bitumen. The performance of the warm VAPEX process was compared to the conventional VAPEX process as a baseline. The packed model was placed in an isothermal bath of circulating hot air to lower the heat loss to the surrounding and to avoid environmental temperature variation between different trials. For each experiment, the live and dead oil production rates, live oil solvent content, solvent-to-oil ratio, residual oil saturation, and asphaltene precipitation analyses were performed. On the basis of the experimental results, the warm VAPEX process provided higher oil production rates at lower solvent requirements compared to the conventional VAPEX process. The oil production rate reached a maximum at the midlevel solvent superheat and with further increase in the extent of superheat, the dead oil production rate became comparable to that of conventional VAPEX but with significantly lower solvent requirement. The increase in the oil production rate was more pronounced in the lower permeability media with higher oil viscosity. For temperatures above the bubble point of the solvent, the solvent-to-oil ratio (SOR) was lower in the warm VAPEX compared to the baseline. The asphaltene content analysis revealed that the asphaltene precipitation only occurs during the warm VAPEX process where the solvent condenses on the bitumen interface while asphaltene precipitation does not occur in the conventional VAPEX process. In addition, asphaltene precipitation decreased by increasing the degree of solvent superheat. The residual oil saturation analysis showed that there is a slight increase in the extent of residual oil saturation by increasing the degree of solvent superheat.