Electrical Submersible Pump Motors Research Articles

Estimation and prediction of motor load torque applied to electrical submersible pumps

This work presents a methodology to model a time series of electrical current using state space approach that aims at estimating and predicting the load torque of electrical submersible pump motors, in addition to classifying the oil well dynamic behavior. For this purpose, the historical values of the stator current of 9 motors from subsea well production were used. To perform the validate the modeling and prediction approach test, one motor is used to identify the model parameters. In sequence, the model is compared with others 8 real motors. The model is also compared with established MATLAB/Simulink motor model. Finally, experimental test using three equipment in operation demonstrated the viability of the method. The torque estimation reached an average absolute percentage error of 2.73% and 5 min forecast presented the absolute percentage error below than 1%. With these results, it was possible to predict variations in the load of an oil well.

Artificial-Sump-Pumping System Improves Production in Unconventional Oil Wells

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 186254, “Improve Production in Unconventional Oil Wells Using Artificial-Sump-Pumping System,” by Reda Elmahbes, Regulo Quintero, and Agnetha Evelyta, Baker Hughes, a GE Company, prepared for the 2017 SPE/IATMI Asia Pacific Oil and Gas Conference and Exhibition, Bali, Indonesia, 17–19 October. The paper has not been peer reviewed. Unconventional oil wells present challenges to electrical-submersible-pump (ESP) systems and can limit production potential. An artificial-sump-pumping system used in unconventional oil wells with steep decline curves and high amounts of free gas has been shown to operate reliably and economically. This paper presents a comparison of conventional ESP methods and artificial-sump systems for which free gas and gas slugs are a challenge. Introduction Unconventional oil wells usually have inadequate reservoir permeability. To enable a significant amount of fluid flow from the reservoir to the wellbore, the wells are drilled horizontally and multistage hydraulic fracturing is performed to expose as much reservoir to the wellbore as possible. The long horizontal laterals create unique production challenges. As the reservoir pressure declines in unconventional reservoirs, gas is released from the fluid and accumulates in hump undulations of the horizontal section. When the gas slugs break free, they create cycling and gas locking that has a negative effect on system performance and reliability. Repeated shutdowns because of gas locking have a negative effect on the production and longevity of the artificial-lift system. Reducing the running time for an artificial-lift system can significantly increase operator capital and operational expenses (OPEX). Some gas slugs can be very large and can create a low-flow or no-flow condition that is challenging for most artificial-lift systems. Therefore, gas slugs must be separated from the liquid before entering the downhole pump to improve production and enhance artificial-lift-system reliability. Designing a system that can avoid slugs and prevent excessive amounts of gas from entering the downhole pumping system is crucial to produce economically from unconventional oil wells. Artificial-Sump-Pumping System An artificial-sump-pumping system is a new form of gas mitigation that uses an ESP artificial-lift method with an inverted shroud that surrounds the entire system. The ESP is equipped with a recirculation system to keep the ESP motor cool during slugs. In addition, the fully encapsulated system has enhanced motor-lead-extension (MLE) protection that helps avoid cable damage during run in hole (RIH), especially for 5½-in.-casing applications. This solution is mainly used for wells that are very gassy and have the potential for gas slugs. Fig. 1 shows a schematic for an artificial sump with a recirculation system. Optional components are recommended to be used on the basis of well conditions and fluid characteristics. For instance, a sand-control system is recommended for applications where sand and abrasive risk is high.

Determination of the temperature distribution of ESP motors under variable conditions of flow rate and loading

Abstract A model to predict the motor temperature of an electrical submersible pump (ESP), under variable conditions of flow rate and loading, has been developed. This model takes into account the coupled behavior between motor, pump and production system. Thus, given a defined frequency in the variable speed drive, the motor temperature was determined as a result of the equilibrium between the heat generation, calculated from the power that the pump demands from the motor, and the heat extraction resistance, calculated from the production flow rate around the motor. Furthermore, in real field operations, the measurement of the motor temperature is made at the lower end of the stator winding, which is not exactly the maximum temperature point. In order to predict the maximum motor temperature value, the model developed in this work determines the motor temperature distribution. A convective heat transfer study has also been made comparing models based on fully developed temperature profile to models that consider the development of the thermal boundary layer. A case study has been made with several oil viscosities and water cut. The results showed a fact commonly observed in ESP field operations, that is, the motor temperature rises when the motor speed is continuously increased. It was also shown that neglecting the effect of the thermal boundary layer development may result in an overheated motor prediction where actually, the motor maximum temperature is much lower than its upper limit. Thus, it was observed that fully developed temperature profile models suffer from inaccuracy when used in viscous oil applications, because of their great thermal entry length.

Performance evaluation of a transformerless multiphase electric submersible pump system

Using of low-voltage variable-frequency drive followed by a step-up transformer is the most preferable way to feed an electrical submersible pump motor. The existence of long feeder between the motor and drive systems usually causes over-voltage problems because of the travelling wave phenomenon, which makes the employment of filter networks on the motor or inverter terminals mandatory. The so-called boost-inverter inherently can solve this problem with filter-less operation as it offers a direct sinusoidal output voltage. As boost inverters have voltage boosting capability, it can provide a transformer-less operation as well. This study investigates the performance of a five-phase modular winding induction machine fed from a boost-inverter through a long feeder. A simulation study using a 1000 Hp system and experimental investigation on a 1 Hp prototype machine are used to support the presented approach.

Performance Evaluation of a Five-Phase Modular Winding Induction Machine

Fractional slot concentrated windings (FSCWs), or modular windings, have shown promise with permanent magnet machines. However, their inability to produce high quality travelling fields has limited their application from spreading to induction machines. This paper presents the design considerations and tradeoffs involved in applying FSCWs to five-phase induction machines using the conventional three-phase lap wound machine as a reference. Previous work has touched upon the application of modular windings to three-phase induction machines, concluding that a conventional distributed winding is superior in terms of torque production and rotor bar losses. In applications such as high frequency induction machines and manually wound electrical submersible pump motors, the proposed machine topology provides advantages that may warrant its application despite an apparent power density penalty. In this paper, a prototype five-phase modular winding induction machine designed to significantly reduce the effect of space harmonics is investigated through simulations and experimentally.

Experimental Investigation of Two-Phase-Flow Patterns and Hydraulic Performance of Electrical Submersible Pumps

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper CSUG/SPE 134089, ’Experimental Investigation on the Viscous Effect on Two-Phase Flow Patterns and Hydraulic Performance of Electrical Submersible Pumps,’ by F.E. Trevisan, SPE, and M.G. Prado, SPE, University of Tulsa, originally prepared for the 2010 Canadian Unconventional Resources & International Petroleum Conference, Calgary, 19-21 October. See Journal of Canadian Petroleum Technology, April 2011, page 45. Using a visualization prototype built from original electrical-submersible-pump (ESP) components and with minimal geometrical modifications, an experimental procedure was developed and conducted to address the viscous effect on liquid/gas two-phase flow through ESPs. On the basis of dimensionless groups that govern centrifugal-pump single-phase performance, two-phase experiments were conducted at different shaft speeds, nonslip void fractions, and viscosity values while liquid rates were kept constant at 60% of the maximum rate at the defined shaft speed. Introduction An ESP is one of the many existing artificial-lift techniques used in the petroleum industry. It consists of a series of small-diameter diffuser-type casing centrifugal pumps, mainly known for their capacity for handling high volumes. Their applications vary from producing high-productivity oil wells onshore and offshore to dewatering coalbed-methane and gas wells. The use of ESPs in liquid single-phase applications is well understood. However, the presence of a compressible phase, such as natural gas, will modify the hydraulic performance of this type of pump. The presence of a second phase often will degrade the ability of the pump to deliver pressure, and depending on the amount of gas flowing through the system, instabilities may occur. These, also referred to as surging, eventually lead to extremely low pressure generation, also known as gas lock. Experimental Description An ESP visualization prototype was designed, built, and installed in a closed-circuit loop. Fig. 1 in the full-length paper provides a graphical representation of the experimental facility. This closed circuit consisted of a 65-gal tank to store the liquid, from which the fluid passed through a booster pump and a liquid-measuring unit before flowing to the ESP prototype. Air was provided by a 1-hp compressor delivering pressures up to 10 psig and flow rates up to 10 scf/hr. Gas was injected at the liquid line close to the prototype intake and measured by rotameters. After passing through the ESP prototype, the fluids returned to the liquid storage tank that also acted as an open-air separator. Both ESP and booster-pump motors were controlled by individual variable-speed drives linked to the acquisition system. This system also received information the differential-pressure and temperature transducers.

Electrical Submersible Pump Rotation Sensing Using An Xy Vibration Sensor

When an electrical submersible pump motor runs, rotary vibrations occur in the same direction as the rotation of the motor. This vibration can be detected by an XY vibration sensor. Depending on the rotation direction, the vibration along the X-axis will be out of phase +90 degrees or −90 degrees with the vibration in the Y-axis. To determine the rotation direction, the vibration sensor measures a vibration of an ESP pump in two axes, recording first and second vibration signals. Next, whether the first signal either leads or lags the second signal is determined by, for example, comparing correlations of the first and second signal with the second signal shifted by plus and minus one-fourth of the period of rotation. Then a direction of a rotation of the electrical submersible pump can be determined responsive to the determination of whether the first signal either leads or lags the second signal.

The Geared Centrifugal Pump: A New High-Volume Lift System

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 123938, ’The Geared Centrifugal Pump: A New High- Volume Lift System,’ by J.C. Patterson, SPE, ConocoPhillips; W.B. Morrow, SPE, Harrier Technologies.; and M.R. Berry, SPE, Mike Berry Consulting, originally prepared for the 2009 SPE Annual Technical Conference and Exhibition, New Orleans, 4-7 October. The paper has not been peer reviewed. The geared centrifugal pump (GCP) is a high-volume artificial-lift system consisting of a progressing-cavity-pump (PCP) -style rotating rod string driving a bottom-intake electrical-submersible-pump (ESP) -style multistage centrifugal pump by use of a downhole speed-increasing transmission. The heart of the system is the unique transmission that uses a novel gearing configuration that allows high torque and power. The GCP provides the high-volume lift of an ESP but with better gas handling, simpler operation, and lower capital and operating costs. Introduction The GCP is an artificial-lift system consisting of the rotating-rod-string drive of a PCP, driving the multistage centrifugal pump of an ESP by a downhole speed-increasing transmission. The transmission is required to increase the relatively slow rotational speed of the PCP rod string, typically less than 500 rev/min, up to the 3,500-rev/min operational speed of the centrifugal pump. The GCP was developed as an artificial-lift system to provide the high-volume lift of an ESP without the expensive and troublesome downhole electric motor and cable of the ESP system. The GCP uses efficient and relatively inexpensive industrial electric motors in the surface drive head, requiring none of the special controls or transformers necessary for high-voltage ESP motors. The rotating rod string transmits power downhole with low power losses. This system combines the highly efficient GCP transmission assembly with a modern ESP pump. This combination results in a system with lift efficiency greater than 50%. Because all of the downhole components of the GCP are mechanical, the design is adaptable to very-high-temperature applications such as steam-assisted gravity-drainage (SAGD) projects. GCP Components Drive Head. The GCP uses the same drive system as a PCP system. A surface drive head turns a rotating rod string that drives the downhole assembly. The only difference between a PCP drive head and one built for the GCP is the load-capacity requirements of the thrust bearing carrying the rod load. In a PCP drive head, the thrust bearing must carry the weight of the rod string as well as the fluid load. Because the rod string of the GCP does not carry any fluid load, the thrust bearing in the GCP drive head can have a correspondingly lower capacity. Another characteristic of both PCP and GCP drive heads is prime-mover flexibility. Although the majority of well locations have electric power, the GCP can be powered by an internal-combustion engine, a hydraulic motor, or an electric motor.

Computation of eddy-current density on ESP motor and well casings under different operating conditions

This paper presents a 2D finite-element analysis of the induced eddy currents on motor and oil well casings of an electrical submersible pump (ESP) oil lifting system. Simulation results revealed that the increase in motor-casing conductivity and/or permeability decreases the eddy-current density on the well casing, contrary to that on the motor casing. Further increase in one or both of these parameters leads to a decrease in both current densities as a result of the skin effect phenomenon. However, the increase of well casing conductivity and/or permeability increases the eddy-current density on the well casing, while that on the motor casing remains unchanged. Increasing the fluid-mixture conductivity does not have any effect on the eddy-current density on the well casing, and for further increase in the fluid conductivity it decreases drastically, contrary to that on the motor casing which remains constant. The higher the current imbalance (including single phasing) and/or motor eccentricity, the higher is the maximum eddy-current density. Consequently, the increase of eddy-current density leads to an increase of the motor and well casings’ temperature, where the latter is known to accelerate the corrosion rate. It can be concluded that the design parameters and the construction of the motor and well casings play an important role in their corrosion.

Comparative investigation of lightning impulse tests on electrical submersible pump motors

This paper investigates the capability of some samples of electrical submersible pump (ESP) motors to withstand standard basic “lightning” impulse level (BIL) and to get the destructive voltage for all phases. Tests were performed on samples from different ESP vendors and with a voltage rating between 1 kV and 2 kV, to fulfill the lightning impulse standard test requirements. All the tested ESP motors showed a decrease in the terminal impedance between one line and the motor casing with the frequency, i.e. low-pass filter effect for fast transient overvoltages. In addition, all ESP motors passed the standard lightning impulse withstand tests with no significant change in the terminal impedance. Used ESP motor failed at 37 pu of the BIL, while all the new ESP motors failed at much lower level up to 22 pu. This trend is attributed to the better oil infiltration in the used motor during runtime than in the new motor with zero runtime.

Withstand capability tests of transient voltage surge suppressors

This paper investigates the capability of some samples of transient surge suppressors (TVSSs), used in electrical submersible pump (ESP) installations, to withstand non-destructive standard impulse tests. Tests were performed on different ratings of the TVSS and with a voltage rating up to 2.5 kV, to fulfill the basic impulse withstand level (BIL) of the ESP motors. On the other hand, used and unused TVSS were also tested by the standard high-amplitude impulse currents to examine the degradation effect. Compared to the (old) TVSS, the used (new) TVSSs gave lower internal leakage current under AC and DC applications. A similar trend was also observed for the high discharge impulse current. This common trend reflects the effect of ageing “degradation” due to the modification of the microstructure of the ZnO elements.

Design and Evaluation of a Preprototype Hybrid Fiber-Optic Voltage Sensor for a Remotely Interrogated Condition Monitoring System

In this paper, we give details of the design and laboratory evaluation of the preprototype hybrid fiber Bragg grating piezoelectric voltage sensor for a remotely interrogated condition monitoring system, such as the measurement system used for monitoring of electrical submersible pump (ESP) motors. The proposed sensor design is directed toward the upper voltage rating (5 kV) of ESP motors.

Hybrid fiber optic voltage sensor for remote monitoring of electrical submersible pump motors

We report on the design and experimental evaluation of the hybrid fiber Bragg grating (FBG) piezoelectric voltage sensor developed specifically for remote monitoring of electrical submersible pump (ESP) motors. Unlike a previously reported transducer based on a single piezoelectric element, the voltage rating of the presented device could be as low as 500 V due to the use of a multilayer piezoelectric stack as the primary voltage-to-strain transducer. This enables the use of such sensors across a wider range of ESP applications, which often have subkilovolt voltage ratings. In addition to the design details, we present details of the full characterization of the device, including the hysteresis and temperature-dependence characteristics and discuss ways of eliminating or reducing these effects. We also demonstrate that the sensor can be used to simultaneously measure voltage and temperature.