Motor Power/Current Measurement for Improving Rod Pump Efficiencies
J.N. McCoy, Echometer Co., A.L. Podio, University of Texas at Austin, Russ Ott, Consultant, Lynn Rowlan, Amerada Hess, Mark Garrett, Yates Petroleum and Mike Woods, Mobil Exploration and Producing US
Copyright 1997, Society of Petroleum Engineers, Inc. This paper was prepared for presentation at the 1997 SPEProduction Operations Symposium, held in Oklahoma City, OK 9 – 11 March 1997. This paper was selected for presentation by an SPE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of this paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented,does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the Society of PetroleumEngineers is prohibited. Permission to reproduce is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O. Box 833836, Richardson, Texas 75083-3836, U.S.A., fax 01-972-952-9435.
ABSTRACT The development of accurate digital measurement ofinstantaneous power during a pump stroke has made possible a very quick and detailed analysis of the efficiency of the pumping system. The efficiency is then used as the benchmark for determining whether a complete well performance analysis is warranted from the standpoint of making best use of personnel and economic resources to increase oil production. In addition, power measurement provides directinformation about lifting cost per barrel of fluid and barrel of oil produced, electrical and mechanical loading of the prime mover, peak power demand, power factor and minimum required ratings. These results give operating personnel information regarding potential problems and give to management a complete picture of the distribution of pumping costs. The power measurements are also converted, bythe software, to instantaneous torque and presented as continuous torque curves for the upstroke and downstroke. This allows determination of the existing level of counterbalance and provides the most rapid and accurate method for counterbalance adjustment to achieve lower torque loading on the gear box and reduced energy utilization. One of the principal advantages of this balancing method is thatcounterbalance adjustment can be made without need for an accurate description of the pumping unit’s geometry which is often unknown or inaccurate. The effect of counterweight displacement on torque and power is observed immediately by repeating the power measurement after relocating the counterweights. This paper presents a series of case studies showing the application of power measurement to avariety of pumping systems and components, including conventional, Mark II, Rotaflex units and high efficiency motors. INSTANTANEOUS MOTOR POWER MEASUREMENT A system was designed and implemented to undertake quantitative measurement of instantaneous power using sensors consisting of two current probes and three voltage leads, which are connected to the three phase leads inside the units switchbox. (1) Special purpose integrated circuits process the sensor data so as to generate an analog signal which is proportional to the instantaneous power. The sensors are calibrated so as to determine the power with an accuracy better than 5% provided the probes are correctly installed. The measurement procedure must be followed closely in order to obtain data of good and repeatable quality. In...