Experimental study of polymer enhanced alkaline flooding for Western Canadian heavy oil recovery.

摘要

Alkaline flooding and polymer flooding of heavy oil have been studied in the laboratory and pilot implemented in Western Canadian heavy oil reservoirs in an attempt to establish alternative waterflooding conversion techniques. As far as the combination of alkali and polymer (AP) flooding, investigations regarding enhanced oil recovery (EOR) are very limited and there are no pilot implementations in Western Canadian heavy oil reservoirs with heavy oil viscosities of more than1000 centipoise (cP).;Alkaline flooding and polymer flooding are carried out individually in order to serve as a baseline confirmation of the effectiveness and potential of AP flooding in Western Canadian heavy oil reservoirs. The response from channelled sandpack AP flooding is compared with alkaline flooding and polymer flooding. The comparison and analysis of pressure drops and recovery performances show that the re-pressurization recovery mechanism dominates the EOR process through synergistic enhancement of alkali and polymer. Improvement and reduction of the mobility ratio, due to viscosity enhancement, are limited. AP flooding not only reduces polymer dosage and mitigates dependency for solution viscosity, but is easily controlled.;A study of AP brine solution emulsification, interfacial tension, as well as viscosity behaviour, shows that AP brine solution makes it slightly difficult to emulsify heavy oil in brine and the minimum 1FT is increased with increasing polymer concentration. AP emulsion is far more stable and AP brine solution can provide a relatively stable 1FT and viscosity within three months.;Improved sweep efficiency for AP flooding was verified. AP flooding modifies the residual oil distribution profile between high and low permeability zones to a greater extent than alkaline flooding and displacement efficiency near the injection site is the highest.;In this thesis, a polymer enhanced alkaline flooding process for Pelican Lake heavy oil with a viscosity of 1202 cP and a total acid number (TAN) of 1.07 mg KOH/g-oil is systematically designed and developed using a channelled sandpack model and produced brine. An integrated approach which includes, emulsification tests, oil/brine interfacial tension (IFT) measurements, viscosity measurements, residual resistance factor (Frr) measurements, residual oil distribution measurements, and channelled sandpack flooding tests is applied. Laboratory studies focus primarily on channelled sandpack flooding tests and simultaneously examine the relevant influential factors including chemical concentration, sandpack length, conversion time, slug size, and brine quality. An optimized formulation of 0.4 wt% NaOH + 0.2 wt% Na2CO3 +1000 mg/l polymer, through trial and error, achieved tertiary oil recoveries of 25--30% original oil in place (OOIP). The high incremental oil recoveries suggest that AP flooding is a feasible and sustainable EOR process for thin Western Canadian heavy oil waterflooding reservoirs.;The channelled sandpack model takes into account adverse mobility ratio, channelling, and reservoir heterogeneity, as well as low reservoir pressure. Specifically, the study takes advantage of heavy oil reservoir characteristics of high TAN, porosity, permeability, and low reservoir temperature. With the use of produced brine, this study provides more reliable and realistic results for field reference.