When it Comes to Progressing Cavity Pumps

Pumps are not living creatures, but with progressing cavity pumps (PCP) that can be a useful metaphor.To get more news about progressive cavity pump, you can visit brysonpump.com official website.

A case in point was a talk listing mistakes that “can doom a PCP to early failure” by Shauna Noonan, a former SPE president, currently a fellow and senior director at Occidental Resources and that day at the SPE Artificial Lift Conference, an engineer with 25 years of PCP experience.

The anthropomorphic descriptions are a product of the interactions within a PCP between the rotor—which moves multiphase fluids through helical cavities in the stator, which is typically comprised of an elastomer surrounding it.

The dimensions of the elastomeric stator change when the rotor begins rotating, increasing the differential pressure inside the pump and adding heat to the elastomer, causing the elastomer to swell and narrowing the tolerances between the rotor and stator. Note that there can be cases where the elastomer shrinks instead of swelling.

“The tolerance between rotor and stator is dynamic. The elastomer is a living, breathing element,” Noonan said.

The list of life-extending tips keeps coming back to understanding how changes to operating conditions, downhole fluids, and reservoir pressures can affect the PCP pump.

Noonan offered a sneak peek at results from a field in the Middle East where PCP run lives were doubled over a 4-year period by simply understanding PCP fundamentals and applying operating and pump selection criteria. The paper, SPE 206909, will be presented at the SPE Middle East Artificial Lift Conference and Exhibition in late October.

The thinking required to improved PCP performance is often counterintuitive. For these pumps, loose is better than tight and not targeting 100% volumetric efficiency downhole is the better long-term bet.

In order to account for the swell that the elastomer will see due to reservoir fluids and temperature, the acceptance pump efficiency from the bench test should not be any higher than 80% at the differential pressure that will be needed from the pump. This is only for low-viscosity fluids. For high-viscosity fluids, the acceptance criteria could be as low as 0% efficiency.
To better understand why that is the case, Noonan strongly recommended a paper by Evan Noble and Lonnie Dunn based on testing at Weatherford. The results showed many instances where the differential pressure across the pump was concentrated towards the discharge, rather than evenly spread over its length (SPE 153944).

The study showed why PCP pump failures often occur at the upper portion of the pump. It included a chart showing the importance of fluid slippage to distribute the differential pressure across the pump. The slippage is highest at 100% lift capacity.

Noonan talked about a field in Canada where the PCPs were failing early at the upper portion of the pump, and since the reservoir pressure had increased due to a waterflood, the differential pressure needed from the pumps was less. This chart demonstrates what occurred in the pumps and that the differential pressure had concentrated much closer to the discharge leading to elastomer failure.

The differential pressure curves will vary depending on the pump design (rotor/stator interference fit), operating speed, presence of free gas, and fluid viscosity. While the specifications can allow an expert an educated performance prediction, bench testing is needed to catch manufacturing defects and collect data needed to predict the interference fit between the rotor and elastomer once in the wellbore.