Low-shear pumping action, responsive control and reliability were critical considerations for enhanced oil recovery (EOR) systems specialist Nalco FabTech when designing and installing a 21-pump polymer injection facility for a Wyoming oilfield. Looking beyond the established plunger-type pumps in general use for polymer injection, the company turned to an alternative.
Polymer injection plays an important role in enhanced oil recovery (EOR). EOR is usually the tertiary stage of an oil field and occurs after primary production and waterflooding. Polymers are used to improve the viscosity and distribution of the injection water through the formation thereby contacting previously bypassed oil and improving field recovery. However, the same chemical properties that make the polymer viscous also make the polymer difficult to dissolve and pump.
Proper handling of the polymer solution is imperative. Preventing degradation due to shear through pumps and pipes, as well as degradation due to chemical incompatibility with brines, are of paramount concern. The sensitivity of the polymer solution imposes limits on the type of pumps that can be used and even some typical designs like centrifugal, gear, and screw pumps are not suitable for this type of chemical EOR.
An Attractive Alternative
Prior to 2004, almost all polymer injection plants built by FabTech incorporated triplex plunger pumps. The Wyoming contract, on which liquid volumes and pressure rating were within the range of the seal-less Hydra-Cell G25 diaphragm pumps manufactured by Wanner Engineering, allowed the company to give serious consideration to this attractive alternative.
The H25 can operate anywhere in the range up to 70 bar, varying flow as required between 1 l/min and 69 l/min. With the addition of new models, the operational scope of the Hydra-Cell pump series is now extended.
A distinctive feature of the Hydra-Cell, giving it an advantage in many applications over other positive displacement pumps, is that there are no dynamic seals or close-tolerance moving surfaces in the design. Smooth, low-pulse pumping action is achieved by the sequential flexing of multiple hydraulically balanced diaphragms within a single compact head — while the diaphragms totally isolate pumped fluid from the drive parts of the pump, which operate submerged in lubricant. Moreover the design minimises internal friction, reducing heat input into the system and further ensuring that the injected liquid reaches its target in effective condition
Seal-less design has implications for the service life of the pump and Life Cycle Costs, by removing the most common cause of premature wear and consequent loss of performance. But equally significant for FabTech on the injection application is the low-shear pumping action of the Hydra-Cell, protecting the polymer from degradation.
FabTech executive Rick Binks admits that his company did not take pump performance claims on trust. “We had to design for pumping a viscous solution containing 800 ppm of high molecular polymers and up to 350 ppm of soda ash (Na2CO3). Not until we had run shear degradation tests with the Hydra-Cell pump in the lab did we move to the next stage.” Controlling pump flow and pressure was not complicated. Output of the Hydra-Cell pump is directly related to its speed, and virtually independent of system pressure. So a relatively simple system using VFD to vary motor speed gives accurate flow control with fast response.
Following the success of the Wyoming plant, FabTech has installed injection plants with Hydra-Cell pumps in Canada and Oklahoma, while additional pumps incorporated in the Wyoming plant include a larger Hydra-Cell model, the H35.