Understanding the Performance of a Progressive Cavity Pump with a Metallic Stator

Analytical and experimental studies were carried out on a progressive cavity pump (PCP) fitted with a metallic stator with a fixed, positive clearance around the single helical rotor. This eliminates wear and greatly increases pump life, but it allows leakage or slip back to suction, which decreases the net output flow rate for a given imposed pressure rise. On the other hand, conventional PCPs have an elastomeric stator surrounding the rotor at zero clearance, so there is zero leakage until this stator wears out. Computations made on three analytical models provided insight into the internal leakage of this new type of PCP and pointed the way for further more definitive performance analysis in the future. These models, which utilized computational fluid dynamics (CFD), were: • Flow past a rotating cylinder between two closely fitted parallel plates, • Flow past a straight wall with a developed (“untwisted”) stator flute moving axially along this wall—like a convergent-divergent bearing space that has wedge flow and the associated developed positive and negative pressures, and • Flow through a slit that models the clearance between the rotor and the surrounding stator (called the “model of the PCP”). Experiments were conducted under single-phase and two-phase conditions in order to acquire performance data for an actual PCP with a metallic stator. Pressure sensors installed inside the pump measured instantaneous cavity pressures and enabled comparison of these measurements with the CFD simulations. Liquid viscosity in the single-phase tests varied from 1 to 480 cP. Light oil with a viscosity of 42 cP was used for the multiphase tests, in which the intake gas void fraction was varied from zero to 80 percent. The test pump had a 40 mm (1.58 inches) rotor and was run over a speed range from 100 to 1200 rpm. The performance curves obtained from the experiments form a valuable database for users who would be interested in applying this new PCP pump type. More significantly, these results validate the use of PCPs with metallic stators in the production of heavy and extra-heavy crude oil.