Experimental Investigation of the VAPEX Process in Vuggy Porous Media

Abstract

Summary In this paper, the application of the vapor extraction (VAPEX) process was investigated to recover Cold Lake bitumen from vuggy porous media with n-pentane as the hydrocarbon solvent. Seven different sintered glass-bead models were designed and fabricated—four of which were vugular media with different vuggy- to total-pore-volume (PV) ratios. The vugs were arranged in aligned and staggered configurations. Three homogeneous sintered glass-bead models of different permeability and porosity were also fabricated to serve as baselines. The vug sizes were controlled in a narrow size-distribution range by embedding wood particles of uniform volumes (20 mm3 each) in the packing of the glass-bead continuum, sandwiched between two parallel glass plates. The packing assembly was then sintered in the muffle furnace. For each particular VAPEX experiment, the oil-recovery performance was characterized by measurements [e.g., live-oil and dead-oil production rates, live-oil solvent content, and Residual Oil Saturation (ROS) (in the invaded area of the models)]. It was observed that the vugs significantly facilitated the live-oil production from the vuggy models compared with the corresponding homogeneous baseline model with the same matrix permeability. The increase in the vug porosity of the porous space significantly increased the live- and dead-oil production rates, and it slightly decreased the extent of ROS in the model. Unlike the sintered homogeneous models for which the live-oil-production rate remains reasonably constant during the lateral spreading phase of the VAPEX process, the vuggy-porosity models displayed a boost in the live-oil production rate when several vugs were being invaded by the solvent vapor. This behavior was more pronounced in the case of aligned vugs in which the vugs were closer to each other, and more vugs were invaded simultaneously compared with the case of a staggered-vug configuration. The enhanced pore-level mixing of solvent with bitumen, the improved petrophysical properties of the porous medium, and the flow communication of matrix with the vugs were found to enhance the live oil drainage towards the production well.