Experimental study of imbibition mechanisms in heavy oil waterflooding using etched glass micromodel

Abstract

Waterflooding in heavy oil reservoirs has an almost 50 years history in western Canada, but its recovery mechanisms, especially in the situation of a high oil to water viscosity ratio, are still not well understood. This thesis studied the water imbibition mechanisms in the process of heavy oil waterflooding, and their effects on oil recovery using a glass made micromodel. In a water-wet environment, waterflooding (water displacing oil) represents a process of water imbibition. This water imbibition experimental study was conducted with varying water injection rates and oil viscosities. The effects of time, viscosity ratio and water injection rate on imbibition rate were studied. The recovery factor was proportional to the square root of time, and it also had a definite relationship with oil viscosity even though it was not linear. The effects of injection rate on imbibition rate were complicated. Images of the imbibition process were recorded and analyzed. Water broke through quickly because of water fingering. A significant amount of oil was produced during the post-breakthrough period under high water cuts. In the cases of low rate water injection, water imbibed into the original oil region perpendicularly to the water channel. At this stage, capillary forces were the key factor. Water film thickening, snap-off and oil refilling were the main mechanisms that made water imbibition work. Emulsification was also another important mechanism observed, with W/O emulsions primarily being formed.