This paper is a progress report an the performance and operation of the pilot polymerflood in the Rapdan Unit. Polymer injection commenced in February, 1986 at a concentration of 1500 ppm. Oue to lower than expected viscosity with produced brine, injection was switched to lower salinity Belly River source water. This change has improved viscosity without affecting injectivity and enabled a decrease in polymer concentration to 1100 ppm. Infill drilling approximately doubled production to 80m3 OPD in 1985. A response to the polymerflood is indicated by a decreasing water/ail ratio and increasing oil production trend. Polymer breakthrough has occurred in several wells but has remained at a very low concentration.
A pilot polymerflood has been implemented in the Rapdan Unit of southwest Saskatchewan. Eleven infill well s, seven producers and four injectors were dri1led on 16 hectare spacing during 1985. There are presently five injection wells and thirteen oilwells on inverted five-spot patterns in the pilot. (see Figure 1) Injection commenced in January. 1986 with polymer being added to the injection water in February.
The Rapdan Unit produces 230 API oil from the Upper Shaunavon (Jurassic) Formation at a depth of 140Om. Oil viscosity is 10cp at the formation temperature of 550 C. The lithology is primarily a dolomite cemented sandstone with a very low clay content. A net pay isopach is shown on Figure 2. The peripheral waterflood which was implemented in 1962 has been only moderately successful due to poor sweep efficiency caused by the high oil/water viscosity ratio of 20 and poor areal continuity.
A study 1 was undertaken to determine the feasibility and to design a polymerflood to improve oi1 recovery in the Unit. Polyacrylamides were selected which developed high viscosity in field injection water and which would not plug the reservoir rock.
Significant incremental recovery potential using polymer after waterflooding was demonstrated in corefloods. Polymer injectivity, which is critical to the Viability of polymerflooding was determined from a field test. A reservoir simulator was used to optimize polymer concentration, slug size, well spacing and pattern type and to predict flood performance. It is estimated that the polymerflood will recover an incremental 12.8% of OIP.
A schematic of the polymer injection facilities is shown in Figure 3. The polymer emulsion product is shipped to the field in tank trucks and transferred to a 64m3 insulated fiberglass storage tank which is heat traced. The storage tank contains a paddle mixer and is blanketed with methane to prevent separation and condensation from occurring. A pump continuously circulates the polymer emulsion through basket filters in the polymer skid unit. From this circulation line variable stroke metering pumps are manually adjusted to inject the desired polymer concentration into the high pressure water injection line. Immediately downstream is a static mixer which breaks the emulsion to allow hydration of the polymer. The polymerized water is then transported to the injection wells and to the formation through internally epoxy coated steel lines and tubulars.