Condition Indicator Developed for All-Metal Progressing Cavity Pumps
Authors: Carpenter Chris 
Published: April 2023

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 209763, “Development of an All-Metal Progressing-Cavity-Pump Condition Indicator,” by John W. Sheldon, SPE, C-FER Technologies; Justin MacDonald, SPE, Athabasca Oil; and Evan Noble, SPE, Technical Consultant, et al. The paper has not been peer reviewed.

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All-metal progressing cavity pumps (AMPCPs) are frequently used in oil and gas applications to produce high temperature fluids to surface but can exhibit accelerated wear during operation that results in decreasing volumetric efficiency over the pump’s life. In the complete paper, the authors present a proposed condition indicator that estimates the wear experienced by an AMPCP at any point in operation and takes into consideration the potential effects of downhole operating conditions. The proposed condition indicator also can be extrapolated into the future and used to estimate the potential remaining useful life (RUL) of an AMPCP.

Introduction
AMPCPs are composed of a metal stator and rotor, which enables them to operate in much higher temperature fluids compared with standard elastomeric PCPs. Because of metal-on-metal contact between the stator and rotor, AMPCPs typically experience more accelerated wear than elastomeric PCPs, resulting in reduced pump efficiency and shorter overall pump life.
While decreasing pump efficiency can be a result of pump wear, it also can be caused by changes in operating conditions, such as increasing pump differential pressure or decreasing pump speed. For this reason, when estimating the state or condition of an AMPCP, pump efficiency alone may be a misleading or imperfect indicator. This paper expands on previous work in the literature by developing a condition indicator that can be used over the course of pump operation to diagnose pump-upset events or estimate the RUL of the AMPCP.

Estimating Pump Wear
Currently, no method exists of directly measuring the wear on the stator and rotor during operation. Earlier researchers proposed an indirect means of measuring stator and rotor wear based on the degradation of the pump-performance curve over time.
The following calculation process is used to estimate the degradation in pump performance relative to a comparatively higher performing reference pump at any point in production. The estimate of pump performance is provided in the form of a pump-wear index (PWI).
1. A reference pump-performance curve is first selected and plotted. This pump-performance curve should correspond to a substantially more efficient pump and allow comparison of the performance of different actual operating pumps. The reference pump-performance curve selected by the authors in the complete paper reflects an operating speed of 200 rev/min.
2. The reference pump-performance curve then is shifted using an equation provided in the complete paper to be the performance curve for the reference pump running at the speed of the actual operating pump. The equation is derived using the assumption that pump slippage is independent of pump speed. The newly shifted reference pump-performance curve is calculated using a corresponding pump speed of 150 rev/min.
3. The volumetric efficiency of the actual operating pump is then plotted based on the pump’s actual operating differential pressure.
4. The degradation in pump performance, also referred to as the PWI, is then calculated as the ratio of the final reference pump speed to the actual operating pump speed.
Thereafter, this procedure is then conducted for each production data point over the course of a pump’s time in operation.