This paper presents the results of several series of laboratory tests evaluating the performance of polymer flooding for heavy oils. The effects of oil viscosity, polymer concentration, displacement velocity, and rock permeability have been studied and results are presented.
Improved oil recovery through polymer flooding was studied by conducting linear displacement experiments in sandpacks with different permeabilities. The viscosity of oil samples used for different experiments ranged from 1000 to 8400 cP. The polymer solution used for this study was high molecular weight polyacrylamide with concentrations of 1000 to 10000 ppm in 1% brine solution.
The results of these experiments show that high polymer concentrations, i.e. more than 5000 ppm, are required in order to improve oil recovery, beyond waterflooding, from a porous media with residual heavy oil saturation. Additionally, effect of injection rate from 0.3 up to 15.4 meter per day was tested and it was observed that slower injection of polymer solutions resulted in higher oil recovery.
It is believed that the results of this study will help develop effective methods for implementing polymer flooding in heavy oil fields, and will give the oil industry a new option for improving oil recovery from heavy oil reservoirs.
Recently, there has been growing interest in this technique for heavy oil reservoirs. At the end of economical life of primary production, waterflooding is performed as a secondary recovery process. It is the most widely used secondary recovery technique. It involves injection of water into the reservoir to improve the recovery of oil. Several successful waterflooding projects in heavy oil reservoirs have been reported, and they show economical incremental oil recovery at high water cut. However, the range of reported recovery is large. Waterflood recoveries of ∼ 1–2% up to 20% original oil in place (OOIP) have been reported for these reservoirs[1]. Miller has discussed the condition of Canadian heavy oil waterflooding projects and has observed that insufficient literature related to this subject has been published. Miller states that the process of assessing performance of waterflooding generally is empirical rather than theoretical, meaning much of the understanding of waterflooding in heavy oil reservoirs is based on observation of the process in the field rather than understanding the fundamental processes involved[2]. Investigation of many waterflooding projects in Canadian heavy oil reservoirs has revealed that these waterfloods exhibit very poor sweep efficiency because of extreme adverse mobility ratio. Jameson[3] reported on waterflooding in the Lloydminster, Saskatchewan, region where the oil viscosity ranges from 500 to over 4,000 mPa.s. Very low incremental recoveries were obtained through waterflooding. Jameson stated that waterflooding was not economical in primary depleted reservoirs. This was a result of increased viscosity of the oil due to loss of solution gases, causing an increasingly adverse mobility ratio between the oil and the injected water.
In order to improve the mobility ratio between the injected water and heavy oil polymer flooding can be used to increase viscosity of water. High molecular weight water-soluble polymers in dilute concentrations (several hundred ppm) increase the water viscosity significantly.
