This paper discusses the feasibility of using crosslinked polymer technology and alkaline/polymer technology to improve recovery in the Grand Forks Lower Mannville 'D' pool.
The Grand Forks 'D' pool is a good quality channel sand with an original oil-in-place of 100 × 106 STB (15.9 × 106m3). The rock has a porosity of 25 % and the permeability ranges from 1000 md to 10,000 md with an average of 3,000 md. The reservoir crude has a viscosity of 11 cp at the reservoir temperature of 88 ºF (31 ºC) and a stock tank gravity of 26 º API. Primary and waterflood oil production has produced 25.5 % of the original oil-in-place as of January, 1986.
Previous model studies and historical pool performance indicated that up to 60 % of original oil-in-place could be left in the reservoir after waterflooding due to gravity effects and high vertical permeability. A scheme of combining the cross1inked polymer technology and the alka1ine/polymer technology has been developed to optimize the ultimate oil recovery.
The crosslinking technology was investigated using cationic and anionic polymers with various crosslinking agents through linear coreflood and viscosity monitoring studies. The alkaline/polymer technology was studied through interfacial tension, fluid compatibility, phase behavior, chemical adsorption, rock dissolution, and coreflood studies. Coreflood studies included injectivity as well as oil recovery studies.
The results of the laboratory studies indicate that the alkaline/polymer system can recover incremental oil over waterflooding of approximately 30 % of original oil-in-place. With an addition of 0.1 % by weight of surfactant, up to 41 % of original oil-in-place can be recovered. No injectivity and fluid incompatibility problems were detected. The test results also indicate that the residual resistance factor can be increased significantly by cross-linking. This should help improve the vertical sweep efficiency by diverting the injection fluids into the unswept lanes. It was concluded that a chemical flood is technically feasible for the subject pool.
The Grand Forks Lower Mannville "D" pool is located in Southeastern Alberta, as shown in Figure1. Figure 2 shows the well configuration of the pool. The pool, which is a lower cretaceous channel sand, is one of the most productive oil reservoirs in the area. The original oil-in-place is estimated to be 100 MMSTB or 15.9 × 106m3. Table 1 lists some of the reservoir rock and fluid properties.
The reservoir has yielded more than 25 million barrels of oil from the Lower Mannville sand since Hs discovery 1n 1968. The field has been waterflooded For more 9 years and watercut has been increasing steadily since then. The pool now has 34 producers and 4 water injectors with a total 1njection rate of 19,500 bid (3,100 m3/d). Current oil production rate is approximately 6,000 bid (950 m3/d) with an average watercut of 80 %.
Previous waterflood simulation study1 and recent production logs ind1cated that there is a substantial volume of moveable oil still in place. The study also showed that the existing waterflood has a good sweep efficiency in the bottom layers, but poorer in the upper layers due to the effects of gravity segregation, high vertical permeability and reservoir heterogeneity.
