The Effect of Reservoir Wettability on the Production Characteristics of the VAPEX Process

Abstract

AbstractBased on the pore-level visual investigation results of vapor extraction (VAPEX) process in etched glass micromodels, two major pore-scale recovery mechanisms were found responsible in the drainage of live oil, namely, 1) the drainage type displacement mechanism of gas invasion in a pore filled with oil and 2) the film flow drainage mechanism in the corners of pore space invaded by gas. Inspired by the role of film flow drainage in the recovery performance and production history of the VAPEX process, wettability was expected to play a profound role in the drainage of live oil by the stated mechanisms. Therefore, we examined the impact of fractional wettability on production characteristics of a VAPEX process at a macro scale. Conventional VAPEX experiments were conducted in a 220 Darcy random packing of glass beads in a rectangular physical model and used n-pentane to recover the Cold Lake bitumen from the oil saturated model. The composition of packed bed was changed from completely water-wet glass beads to completely oil-wet treated glass beads, at different compositions obtained by mixture design. It was found that the live oil production substantially increased (35-40%) from water-wet conditions to the extreme case of oil-wet conditions. A percolation threshold at about 65% oil-wet composition (35% water-wet) was found, after which the live oil production rate during VAPEX process did not change with further increase in the volume fraction of oil-wet beads. The production rate of VAPEX linearly decreased with increasing the volume fraction of water-wet beads over the 30% value in a random packing. It is believed that above the percolation composition, the oil-wet regions dominate the film flow process as there will be a continuity of high conductivity film through oil-wet regions, as a result of thicker (in size) bulk oil films between particles. The solvent content, the solvent-to-oil ratio (SOR), and the residual oil saturation did not correlate to the wetting composition of packing. The values obtained for solvent content were 47-49% (g/g), for the SOR 0.9-0.95 (g/g) and for the residual oil saturation 7-to-10 % of pore volume.