Experimental Investigation of Wellhead PCP for Gas Well Deliquification

A Progressive Cavity Pump (PCP) was evaluated for use as a multiphase pump. The pump is a 576 gpm, constant wall thickness PCP operating with an air/water mixture. Thermocouples were installed along the length of the pump to monitor the elastomer temperature to determine when excessive temperatures were present. Inlet pressures of 15, 30, and 45 psig were considered with pressure rises of 30, 60, 90, 120, and 150 psig. The GVF’s considered were 20, 40, 60, 90, and 98%. It was determined that with the water and air mixture, 98% was the maximum GVF at which the pump could operate continuously. The volumetric efficiency, pump effectiveness, and mechanical efficiency were calculated. The temperature rise across the pump was small, so an isothermal flow was assumed. The PCP investigated has a steel rotor and an elastomer stator that were manufactured with an interference fit. This resulted in volumetric efficiencies above 95% for all test conditions at full speed. This interference fit produces a significant drag on the rotor which is relatively constant at a given speed over the entire operating range considered. This results in the mechanical efficiency being low, 15 to 20%, for ΔP = 30 psig but approaching 60% at ΔP = 150 psi for 0% GVF. The mechanical efficiency decreased with increasing GVF to a low of 28% at ΔP = 150 psi for 98% GVF. The GVF specified here is the actual GVF passing through the pump. If a liquid recirculation system were added to the pump reducing the GVF in the pump, higher efficiencies and the ability to operate at 100% GVF for the process fluid entering the pump system can be obtained.