Polymer Supply Pump

Choke

Injection Well 1

Injection Well 2

Injection Well 3

Injection Well 4

Non-shearing Polymer Flow ControlBy Ken Krewulak of Canadian Natural Resources

Polymer flooding is used as an enhanced oil recovery fluid in the oil industry. When multiple wells are connected to a single supply of polymer (figure 1), the need to control the flow rate of each polymer injection well is required. As polymer is a “shear thinning” fluid, common mechanisms of flow control, such as chokes, damage the polymer and reduce the viscosity of the injected fluid. The need to control the flow rate of polymer without shear degradation is required to effectively implement the polymer flood.

The shearing of polymer in chokes occurs due to the immediate pressure drop and extreme velocity of the fluid as it passes through the orifice. If the pressure drop could be extended over a longer length the damage to the polymer is reduced and in most cases eliminated. A method to extend are in which the pressure drop occurs is to utilize the pipe wall friction of small diameter pipe. Testing was completed and it was found that ½” pipe was the smallest pipe diameter that would not shear the polymer at injection rates up to 175m3/day. It was also discovered that ½” pipe at a flow rate of 150m3/day with a 1500ppm polymer solution would impose a pressure drop of about 22kPa/meter and with a 100m3/day flow rate the pipe friction imposed about 18kPa/meter.

A device (Figure 2) was constructed with a total length of 620 feet (190m) of ½” pipe with a designed back pressure of 4500kPa at a flow rate of 150m3/day of 1500ppm polymer solution. The device was fabricated with 5 coils with different lengths that allow the flow length to be changed from 620’ down to 0’ in 20’ increments. To change the flow length, a valve is either opened or closed to achieve the desired pressure drop and or flow rate.

From multiple tests completed the device has proven to be very effective at controlling the flow of polymer without shear. The viscosity of the polymer entering the device is equal to the viscosity leaving the device. The device will prove to be valuable tool to polymer floods that are newly under flood and have wells on vacuum, or on floods that have polymer supplied to many wells from one pumping source.

Figure 1 – Chokes replaced with the “non-shearing polymer choke”

Coil 120’

Coil 240’

Coil 380’

Coil 4160’

Coil 5320’

Figure 2 – Non-shearing polymer choke schematic

Initial Prototype

Current Production Model