Subsurface Electrical Pump Well Test Analysis

Abstract

Abstract The subsurface electrical pump, a relatively high volume type of artificial lift, is most applicable in wells that are under the influence of a strong waterdrive or waterflood and have nigh watercuts or low GOR's. The economics of producing these high watercut wells is directly producing these high watercut wells is directly related to the cost of electrical energy used and the operating life of the equipment. To optimize the electrical cost and operation life, one must understand the basic characteristics of the motor, centrifugal pump and cable. This paper covers those basic concepts and presents a paper covers those basic concepts and presents a well test analysis technique and indicates the corrective steps to be taken to accomplish a lower cost per barrel of fluid lifted. Introduction In the spring of 1968, Continental Oil Co. initiated a program to determine the causes of poor subsurface electric pump performance. An poor subsurface electric pump performance. An analytical system was developed to evaluate the performance of subsurface electric pumps. The performance of subsurface electric pumps. The results of the analysis indicated the need for company schools at which operating personnel and engineers could become familiar with the proper selection and operation of this equipment. The first 1-week school was held in Nov., 1969. This paper primarily covers the well test analysis, but prior to discussing the well test form, it is necessary to review important aspects of the subsurface electric pump. Each portion of the pump will be discussed with portion of the pump will be discussed with major problem areas stressed. Subsurface Electric Pump Description A typical subsurface electric pump arrangement is shown in Fig. 1. The electric motor is on the bottom of the assembly. Above the motor is the thrust bearing and seal assembly, the pump intake, and the multiple-stage centrifugal pump, which is attached to the tubing string. This allows all produced fluids to enter the wellbore below the electric motor and flow around the motor to the pump suction. The electric motor driving the centrifugal pump is a two-pole, three-phase, squirrel-cage, pump is a two-pole, three-phase, squirrel-cage, induction motor. These motors run at 3,450 rpm on 60-cycle current. Variations in the cycle frequency cause a variation in the motor rpm. This is not a problem when using most purchased electrical power. The design and operating voltage of these motors can be as low as 220 v and as high as 2,300 v. The shaft output of these motors may be from 1/3 up to and including 520 hp. The wellbore fluids must absorb the heat that is generated within the motor. Experimentation has shown that the wellbore fluids must pass the motor at a minimum rate of 1/2 to 3/4 ft/sec in order to cool the motor properly. properly.