- Active Magnetic Thrust Bearings
- Passive Magnetic Radial Bearings
- Hermetically Sealed High Speed PM Motors
- Hybrid Compressors
- Magnetic Coupling
- Autonomous Control
- Sensorless Long Step-out Variable Speed Drives
- Flow Through Motors
- PM Motor as Magnetic Coupling
Active Magnetic Thrust Bearings
Mechanical thrust bearing reliability has been proven on rotating turbomachinery when the environment (in contact with the bearings) and the related process that impact bearing loads are well controlled, in addition to sufficient lubrication provided both for thermal and friction characteristics. Unfortunately for downhole applications, the control of both the environment and the process is very limited. The dynamic fluid in the downhole environment is subject to constant changes in pressure and temperature that can affect bearing loads. In addition, measures taken to exercise some level of control in this volatile environment are complex and bound by significant limitations.
Proven Reliability and Availability
Magnetic bearings have proven their reliability and availability in topside oil and gas applications, as well as demanding subsea applications. Upwing Energy is bringing this proven technology to downhole applications and, more specifically, to thrust bearings, where control of position is necessary to optimize performance. The value of a thrust magnetic bearing for downhole rotating equipment is significant:
Thrust force with non-contacting surfaces
- No friction, no wear surfaces to degrade over time
- No sealing or providing a clean environment for long operating life
- No change in performance with gas, liquid, or anything in-between
- No generation of heat to manage
- Not effected by radial or axial vibrations/unbalance
Real time data on the acting thrust forces
- Health monitoring data for prognostic and diagnostic capabilities
- Active monitoring of real time operating conditions, such as surge or gas lock created by hydraulic systems
- Detecting and monitoring vibration and equipment balance issues
Easily Accessible Controller
For easy access and data collection, the controller for the magnetic bearings is placed topside, along with the variable speed drive (VSD) for the motor. The electronics and controls have been optimized to maintain rotor position control in the downhole system from over 12,000 feet. Topside controls significantly increase the availability of the bearings well beyond conventional mechanical bearings. The change out of the controller can be performed within minutes, instead of having to pull out the complete pump system in the case of a conventional mechanical bearing system failure.
Hermetically Sealed Components
The electrical coils utilized to control the axial magnetic flux/ force are hermetically sealed, similar to the motor, and isolated from the environment. In an environment where the liquids, gases, solids, or pressures are constantly changing, the hermetically sealed components have no mechanical or electrical connection to the rotating shaft, where the shaft is held in position via a magnetic field generated and controlled by the magnetic bearing.
A thrust magnetic bearing system for downhole rotating equipment allows for adequate operating clearances between rotating and nonrotating parts for fluid to pass, eliminating the need for seals and complex, costly barrier fluid systems or protection bag/bellow systems. Particulate material in the process fluid is free to flow through the large clearances without affecting operation. The clearances also allow for use of an isolation barrier to allow operation independent of the environment without any lubricants or cooling that may reduce system efficiency and performance.
Higher Speed Operation
Turbomachinery is moving to higher and higher speeds to enhance performance, increase efficiency and reduce the size of the rotating equipment. The shortcomings of conventional mechanical thrust bearings as speed is increased, such as higher losses, are well documented. This phenomenon is exacerbated in a compressor system where the speeds are 10 times that of a downhole pump system, and the production fluid is in a gaseous form rather than liquid. A magnetic thrust bearing is the only viable solution to provide the performance, reliability and benefits of real time monitoring that such a system needs to be successful for this application.
Upwing Passive Magnetic Radial Bearings
Downhole rotating tools have a significant number of radial bearings for supporting the rotor; having over 100 radial bearings in one tool is not uncommon. These mechanical sleeve bearings require active lubrication, which can be the production oil, water or an isolated lubrication supply, to operate for extended periods of time. Transient conditions, such as gas lock and contaminates in the fluid, can significantly impact conventional mechanical radial sleeve bearing performance and operating life. In a downhole compressor application where the speeds are 10 times the speed of conventional downhole pump systems and no fluid is available, a non-contacting high-speed bearing system is an enabling component, since conventional bearings are not able to have an economically viable life.
To address reliability, availability and cost, Upwing has developed a unique passive magnetic radial bearing. Upwing’s Passive Magnetic Bearing™ (PMB) does not require any controllers on the topside.
How Upwing Passive Magnetic Bearings Work
Upwing PMBs utilize permanent magnets of identical polarities in both the shaft and the stator to magnetically support the shaft. Having magnets of similar polarity in proximity to one another creates a repulsion force that keeps the bearing shaft radially suspended in a magnetic field. While the shaft is suspended within the stator magnet assembly with no mechanical contact between rotating and non-rotating components, it can have a rotation about a longitudinal axis that is not reduced by surface-to-surface friction typical of fluid film bearings. Furthermore, the shaft can operate with significant fluid gaps, over 20 times the gaps of conventional mechanical bearings, without any active controllers on the top side and no wear or friction created between the rotating and non-rotating surfaces.
The magnets, imbedded in Inconel and hermetically sealed from the environment, provide radial stabilization without contact and are not affected by the fluid properties (liquid, gas, pressures, temperatures, etc.) present in most wells.
Furthermore, the passive radial bearing performance is not effected by the imbalances caused by fluid dynamics or mechanical changes to the rotating parts, such as imbalance, pitting, erosion of hydraulic sections, etc. The radial passive magnetic bearings allow the shaft to rotate about its mass center as the rotating components wear, and does not transmit vibration to the non-rotating components within its design criteria.
Upwing Smart Damping System for Low Resonate Frequencies
The Upwing Smart Damping System™ (SDS) is used to damp the low resonate frequencies of the shaft and housing that are excited by the rotation of the shaft. The SDS system only focuses on damping low frequency shaft rigid body and housing resonances, and ignores higher frequencies, such as synchronous displacement, allowing the shaft to rotate about its mass center. This minimizes the SDS power and damping required during nominal operation. A SDS magnet is radially imbedded into the bearing shaft in conjunction with a passive radial bearing shaft magnet assembly. Each pole of the damper magnet is equipped with magnetically conductive pole shoes to ensure uniformity of the magnetic fields generated by the damper magnet around the rotor axis. A damper sleeve is installed over the outer diameters of the damper magnet, and the damper pole shoes to hold them in place and prevent relative motion during rotation, and hermetically seal the magnet from the environment.
Whether for slow speeds for pumps or higher speeds for compressors, the radial passive magnetic bearings are fully compatible with the working fluids of an oil or gas well, can support a rotor in almost any environment, and do not have any wear characteristics that impact the life of the bearing, making them the ideal non-contact bearings for all downhole applications.
Hermetically Sealed High-Speed Permanent Magnet Motors
Permanent magnet (PM) motors have just recently been introduced into downhole equipment. PM motors have proven their superior performance and cost effectiveness in numerous industries. They have been used in everything from high precision, high reliability applications in the aerospace industry to low cost, high volume applications in the automotive industry.
More and more industries are adopting PM motors over induction motors due to the added value they offer, including higher energy density, higher efficiency (lower heat generation), higher speed capabilities and ease of fabrication. PM motors also offer the ability to integrate them into rotating tools to optimize the complete system, enabling applications that would otherwise not be feasible.
Upwing Energy’s parent company, Calnetix Technologies, is the world leader in the system level integration of PM machines in a wide range of industries worldwide. Applying Calnetix’s knowhow, Upwing is integrating PM motors into its downhole rotating equipment. In doing so, we are able to leverage the unique capabilities of PM machines for our Subsurface Compressor Systems (SCS) and Magnetic Drive Systems (MDS). Some of the unique features and key values that Upwing’s hermetically sealed high-speed PM motors provide are discussed below.
Left: Our complete rotor system (mostly magnets and other proprietary components) is hermetically sealed within Inconel. Right: Our stators initially are varnished with a vacuum pressure impregnation (VPI) process. All varnished copper wires are potted, and the complete stator is inserted into a hermetically sealed chamber for the upmost protection and reliability.
High-speed operation is a must for compressible fluids, especially in a restricted diameter environment. High speed also brings about unique value for pump systems. For PM motors, speed is directly proportional to horsepower (HP). PM machines provide constant torque throughout an operating speed range, therefore increasing the speed directly increases the HP. For example, if a motor with a fixed geometry delivers 200HP at 3,000rpm, the same physical size PM motor will deliver 400HP at 6,000rpm. Or, a 6,000 rpm 200HP motor will be half the length of a 3,000 rpm 200 HP motor. High speed also has significant value for pump systems; as the pump speed doubles for electric submersible pump (ESP) applications, only one-third of the pump stages are necessary to perform the same amount of work. This significantly reduces the overall pump size, cost and handling complexity.
Larger Air/Fluid Gaps
Conventional induction motors, which dominate the downhole rotating equipment, achieve 85 percent efficiency with an approximately 1 mm air gap. PM machines achieve efficiencies over 90 percent with an approximately 13mm air gap. This is due to the high magnetic field created by permanent magnets vs. energizing coils. This ability to operate with large clearances between the rotor and stator allows for larger air/fluid gaps for PM machines, reducing fluid drag losses and enabling the capability of canning or sealing the motor from the environment in production fluid flooded applications.
Lower Heat Dissipation
Magnetic losses are generated when magnetic field variations cause losses in magnetically and/or electrically conductive materials. The high strength magnets positioned on the rotor that provide the magnetic field (vs. coils that need to be energized) in a PM machine serve to minimize any field variations to which the components on the rotor may be exposed. Thus, there is very minimal rotor heating on a PM machine, which is one of the reasons why PM machines have such high efficiencies. This factor alone provides an approximately 10 percent efficiency increase in favor of PM motors over induction motors for a majority of applications.
But, existing ESP topologies cannot take full advantage of PM motor benefits by replacing an induction rotor with a PM rotor. The limiting factor of delivering HP in ESP applications is thermal management (i.e. the removal of heat from the motor). In conventional ESP motors, which operate in liquid filled chambers that have a balanced pressure with the environment, the friction losses generate more heat than the motor electromagnetic losses. This heat must be removed from the motor and put into the pumped fluid, where the only path is through the housing over the stator. Therefore, replacing an induction motor rotor with a PM rotor will not have significant value because the same amount of friction losses are generated with the PM rotor, and the same poor conduction path for heat to the production fluid is present. In order to take full advantage of PM motors, specifically for downhole applications, a system level approach is required.
Isolation from Harsh Environments
In order to deliver the full potential of PM motors, Upwing Energy has developed a unique motor and hydraulic architecture for both the SCS and MDS.
For the SCS, the complete motor section is hermetically sealed to isolate the motor from the outside environment. The motor operates in an inert gas at atmospheric pressure with large gaps, and therefore, does not generate significant friction losses even at 50,000rpm. The torque is transferred from the motor to the compressor via a magnetic coupling. The heat, which is mostly generated in the stator component of the motor, is cooled through the flow of the gas over the surface of the sealed chamber.
For the MDS, the PM motor assemblies are completely canned. The stator and rotor are independently hermetically sealed and operate with a large clearance. The PM motor is integrated such that the separate rotor can be retracted along with the pump section independent of the stator, as the stator is part of the permanent completion. This flow through architecture not only provides cost effective rotor retrievability without the need to affect any electrical connections or the permanent completion downhole, but also provides direct access to the production fluid as a coolant medium to the maximum motor surface area to increase the heat dissipation. Upwing MDS PM motors are on the order of five times the energy density of conventional induction motors due to their open architecture that is able to dissipate more heat and to run to higher speeds (over 6,000rpm).
The Upwing Magnetic Drive System™ (MDS) flow through architecture
Combining all the unique features of PM motors along with Upwing’s system level integration ensures the most energy dense, compact and efficient hydraulic system that maximizes reliability, availability and retrievability of downhole rotating equipment.
Upwing’s hybrid multiphase subsurface compressors are used as a form of artificial lift for gas wells to increase wellbore drawdown at the compressor intake and pressure boosting at compressor discharge. The increased gas production ranging from 20 to 150% from the use of a subsurface gas compressor in gas wells demonstrate the same effects of increased drawdowns by artificial lift in oil wells.
Upwing’s compressor topology is composed of multiple stages of rotating and non-rotating hybridized axial compressor blades. Similar to the compressor section of a jet engine, the Upwing hybrid multiphase compressor can handle significant liquid content. To date, the compressor has operated in an extensive wet gas well (142bbl/mmscf) without any signs of erosion or corrosion due to liquid content.
Upwing has performed extensive parametric studies to evaluate the different degree of impacts by various reservoir, well geometry, and compressor factors on well productivity with downhole artificial lift. Simulations from Upwing’s Enhanced Production Simulator (EPS) based on actual well data have provided key insights on how to plan well completion geometry and leverage the capability of subsurface compression to maximize the production gain potentials.
Wide Operating Range
Upwing compressors are designed to have wide operating ranges to compensate for the flow and pressure fluctuations during the life of a conventional or unconventional gas well. Furthermore, due to straight flow path and large gaps between the stator and rotor blades, by design, the compressors can handle particles up to 200µm. Continuous testing is being conducted in Upwing’s flow loop to better characterize the compressors at higher levels of liquid content in the gas stream as well as larger particles to further optimize design.
Similar to ESP systems, a significant number of compressor stages can be stacked to reach the desired pressure ratios at given flows and temperatures.
The topside autonomous control system monitors in real time the health of Upwing’s compressor and adjusts the power and speed via the topside variable speed drive (VSD) to ensure the compressor is operating within the desired window to avoid surge conditions.
Liquid Loading Solution
The combination of Upwing compressors’ characteristics, such as increasing reservoir drawdown, accelerating the bottom hole gas velocity at the suction point and increasing the pressure and temperature of the gas at the discharge point as well as the gas velocity at the well bore, enables significant liquid carryover to the surface and postpones liquid loading without the use of the water pumps that are commonly used in gas wells today.
Water ingestion in a 6-stage axial compressor
Upwing Magnetic Coupling
In order to isolate the motor and other electrical components from the downhole environment, Upwing utilizes a magnetic coupling to transfer torque from the electric machine to the hydraulic section. The patent-pending Upwing magnetic coupling can operate with large clearances and transmit high torque from very low speeds for pumps (1,000rpm) to very high speeds for compressors (over 50,000rpm).
Enables Protector-less Configuration
Upwing’s radial gap type coupling includes an inner rotor that is contained within the sealed housing, and a surrounding sleeve to protect the magnets that generate a magnetic field. This inner rotor is designed to be exposed to the downhole fluids, offering a fully sealed assembly capable of operating in the high pressure, high temperature well bore environment for the life of the device. The outer rotor of the magnetic coupling is sealed with the PM motor in a hermetically sealed section that is maintained at a low pressure gas environment, since it generates higher windage losses due to its larger diameter. This configuration allows for the minimal fluid friction losses and does not require any special cooling. An isolation sealing can between the inner magnets and the outer magnets allows for magnetic field alignment for torque transmittal from outer to inner rotors without any slippage. The Upwing magnetic coupling allows for any downhole rotating system to operate without the need for complex sealing (i.e. protector-less).
Increases Operating Life
Upwing is able to offer the most advanced drive system in the industry due to its unique and proven knowhow in the use of magnet devices in the downhole environment. The Upwing magnetic coupling allows for the motor system to be fully isolated from the downhole environment, providing the motor operating life typically only seen in surface applications (or not seen in well applications before). The ability to configure the Upwing coupling with the clearances and the torque capability necessary within the constraints of the wellbore, and deliver the operating life desired by well operators, is a step change in the industry.
Current artificial lift systems have certain elements of control. For example, the Subsurface Compressor System (SCS) and the Electric Submersible Pump (ESP) use a variable speed drive (VSD) on the surface to control their motors downhole. There are also other elements in the well system that provide either information or actuation to control the well. For instance, operators install downhole sensors to measure the temperature and pressure of a well at different depths. However, these elements are seldomly linked together to provide better control of the overall system. Even if the information from different elements is used to improve the performance of the well, it is often used in an ad-hoc and non-real-time fashion by engineers located remotely after the fact. The adverse situations must be handled in real time in-situ by a system level control scheme to avoid damages to the downhole equipment and to ensure continuous operations of the artificial lift system. There is a need to link all of these elements together to achieve optimal performance of the system.
Block diagram of the SCS system
The SCS has several plants (e.g. motor, bearings and compressor), actuators (e.g. PM motors to generate rotation, bearing actuators to levitate rotors, bearing damping actuators to dampen the vibrations, and compressors to increase the gas pressure), sensors (e.g. motor back EMF voltages, bearing sensors and bearing damping sensors), and controllers (e.g. VSD and magnetic bearing controller (MBC)) throughout the SCS system. The VSD was originally designed to control SCS and ESP motors. The MBC can control the magnetic bearings in the SCS.
Without an autonomous system control scheme, as the environment changes, the motors will only respond to the VSD’s control commands, while the bearings will only respond to the MBC’s control commands. For example, if an environmental change affects the bearing performance that can be mitigated by varying the motor speed, then in the current configuration, this action can only be done by an engineer. To avoid damages to the downhole equipment, the engineer notified by the MBC must have the knowledge to analyze the information and make the right decision about what actions to take on the VSD, must have access to change the setting of VSD, and must act in a timely fashion. Therefore, for faster response and to eliminate human error, there is a need to have an autonomous control at the system level to protect and optimize artificial lift systems.
How Autonomous Control Works
The autonomous control of the SCS
As shown above, energy is transmitted into the SCS from the surface (as indicated by “Electricity”). The motor will convert the energy to torque and transmit torque to the compressor via a thrust bearing unit. The compressor will convert the torque to the pressure ratio of the gas flow across the intake and discharge of the SCS. With the pressure ratio by the SCS, there will be a lower downhole flowing pressure (as indicated by “Drawdown”) generated in the wellbore to induce more gas production. The thrust loads from the compressor will be taken by the thrust bearing unit.
An autonomous system controller links all the elements to control the whole system without human interference. Each plant (e.g. motor, bearing, etc.) could have its own controller. The information (as indicated by “Info”) from the sensors of a plant will feed into both the plant controller (e.g. motor controller, bearing controller, etc.) and the system controller (as indicated by all the red lines shown). For example, the position sensor in a magnetic bearing will send the information about the rotor position to both the bearing controller and the system controller. With the information from some of the sensors (sensors of the plants or other external sensors), the system controller, based on a predetermined autonomous control scheme (algorithm with logics), will decide what action to take by sending out control commands (as indicated by all the green lines) to the actuators in the plants to optimize the operation of the system according to an initial setting (as indicated by the “Setting”). In the meantime, the system controller will also send the information from the sensors to the surface (as indicated by “Monitoring”) to set off alarms, display in a monitor for the engineer to review in real time, or store in a database for later use.
To summarize, a system controller uses information from the SCS elements and other external sensors to take appropriate actions autonomously. This will help optimize the performance and reliability of the SCS system in-situ without the delay of decision-making and manual control by personnel located remotely.
Four types of autonomous control schemes
There are four types of autonomous control schemes as shown above. When a system (either SCS or ESP) is surrounded by its environment, both the system and its environment can be either active or reactive.
When the environment is actively/constantly changing, the autonomous system controller will receive the information about this change from the sensors. The system control will take appropriate actions to ensure that the system will reactively keep up with the environment in order to maintain the operation of the system. Under these circumstances, when the environment makes the first move and the system catches up autonomously, the autonomous control is in the mode of optimization of system performance under external disturbances (as shown in the lower right corner of the table).
The system can also actively change the state of operation to induce changes to the environment (as shown in the upper left corner of the table), particularly inducing changes to producing reservoirs. The purpose to do so is to understand the reservoir responses to the changes of the SCS. In this case, the SCS is performing a programmed well testing, wherein the pressure measurement records form the basis for transient well-test analysis and are primarily used for determining reservoir-rock properties and producing-formation limits.
When both the system and its environment are not active (as shown in the lower left corner of the table), there is information from the sensors in the meantime, indicating that some of the SCS parameters are deviating from its set values, and there could be deteriorations of the SCS components causing it is to move away from its operating point without active changes from either the SCS or its environment. In this situation, the system controller can set off alarms on the surface to indicate the need for maintenance on the SCS. Essentially, the system controller is performing diagnostics (or even prognostics) of the SCS.
Instead of responding to the changes of the environment, the system controller can predict the changes of its environment and the SCS itself, and can proactively change the state of the SCS operation to ensure that it always stays in the optimal operating conditions. To ensure that the SCS can always adapt to its environment, the knowledge of how the reservoir and SCS will evolve with time is required upon the installation of the SCS in the well. In this case, both the SCS and its environment are active (as shown in the upper right corner of the table).
Sensorless Long Step-out Variable Speed Drives
In downhole applications, motors in the wellbore are needed for downhole pumping, compressing or blowing of well fluids to enhance fluid recovery and process flow. Downhole device operating speeds are determined by the process fluid and method of enhancement to the fluid flow, therefore the right operating speed for the specific hydraulics is necessary to optimize the process. The speed range for Upwing downhole equipment can vary from 3,000rpm for heavy oil to 50,000rpm for pure gas compression. As the operating speed increases, the value of the variable speed drive (VSD) system becomes significantly important.
Upwing variable speed drive and interconnect diagram.
By utilizing cutting-edge technology in motor drives, Upwing is able to take full advantage of the latest technology in permanent magnet (PM) motors for downhole applications. Upwing sensorless drive systems can operate and control PM motors over 60,000rpm from the surface of a well over 12,000ft downhole without sensors and able to catch the motor’s spinning rotor on the fly without bringing the complete downhole rotating system to a full stop.
Upwing’s drives are optimized with the whole system in mind. In particular, the drives have features that maximize the efficiency of the drive, such as space vector modulation and dynamic deadtime insertion in the switching patterns of the power devices. Additionally, the total harmonic distortion (THD) of the machine currents and grid side currents are controlled to a low value. This reduces the losses in the machine that is connected to the drive, which in turn, increases the efficiency of the machine. Also, dynamic operations resulting from sudden speed or torque demand are managed by sliding mode control mixed with optional back emf feedback. The VSD control hardware consists of a rugged dual core processor capable of operating up to a PWM switching frequency of 60 khz. The processor also is capable of operating at an ambient temperature of 125°C
Upwing’s VSDs are designed to drive high-speed machines and machines with low impedance. This is achieved by switching the power devices of the drive at a high frequency that is synchronized to the fundamental frequency of the machine. Consequently, the fundamental frequency of the machine can be high without incurring a large distortion in the current that is drawn by the machine.
A VSD designed for an optimized low impedance machine can drive high impedance machines without any changes. Therefore, machines running applications that require long step-outs, automatically appear as high impedance machines to the VSD output and can be driven without any major difficulty.
The distortion is further decreased by dynamically adjusting the inserted deadtime in the switching patterns of the power devices. In addition, Upwing’s high frequency drives include a simple inductance filter, which further reduces the distortion of the current that is drawn by the machine. In fact, the filter limits the maximum distortion of the machine currents. In other words, the drive does not need to rely upon the machine inductance to limit the distortion in the currents that are drawn by the machine. The combination of high switching frequency that is synchronized to the fundamental frequency of the machine, dynamic deadtime insertion, and a simple inductance filter make Upwing’s high frequency variable speed drives an ideal choice for low-impedance and high-speed machines.
Active and Passive Grid Rectifiers
Upwing’s VSD is designed with both active and passive grid rectifier options built in. Based on the grid condition, the rectifier option can be selected through the control settings. The ability to choose between these two options is a distinguishable feature of Upwing’s VSDs, which are not offered or incorporated by commercial VSD manufacturers. The advantage of an active rectifier is that it offers very low current distortion to the grid; also, it can operate at a wide input voltage range.
In remote areas, the grid is typically soft, and in most cases, is generated by simple single phase to three phase rotary converters. An active rectifier at the front end of the VSD provides low harmonics but in some cases can result in unstable input voltage. In such installations, a passive option can be enabled to prevent oscillations if the grid can tolerate higher harmonics.
Reliability and long operating life are at the forefront of importance in the design of Upwing’s power electronics drives. This is obtained by keeping the electrical and thermal stresses on the components within the drive to reasonable levels. The reliability of Upwing’s drives is further increased by reducing the parts count in the drive. In particular, the avoidance of requiring position feedback from the machine and voltage feedback for the machine greatly increases the robustness of the drive. All Upwing drives go through rigorous electrical and thermal testing before they leave our factory, minimizing manufacturing and component infant mortality issues. High reliability, reasonable stress levels and rigorous testing result in the long product life spans of our variable speed drives.
Upwing’s variable speed drives are re-programmable in order to meet the requirements of applications. This is achieved through the use of generic embedded software and unique parameter files that are customized for a particular application. Typical drive characteristics, such as current limits, overspeed limits and acceleration rates are readily changeable. For applications that require unique capabilities, the embedded software also can be modified. The ability to re-program the embedded controllers coupled with the ability to customize the drive hardware allows our drives to meet the needs of different applications.
The data interface and communication channels of Upwing’s VSDs also enable autonomous control of our downhole rotating devices. The VSD control has ground fault protection. In the event of a ground fault, the control will shut down. External protective relays, such as Beckwith or Basler protective relays, can also be used.
Flow Through Motors
A byproduct of converting electrical power to mechanical work is heat. The only way to remove heat in electric machines is through heat transfer into the surrounding environment by either conduction, convection or radiation. The less heat that is generated by an electric motor, the less heat dissipation that is required to keep the temperature under the design limits.
In the application of downhole rotating tools, especially electric submersible pumps (ESPs), heat generation is further exacerbated by mechanical losses due to the friction of the motor rotor spinning in the pressured motor oil system that protects the electrical components of the motor. Therefore, for ESP applications, the torque delivered by the motor is directly limited by how much heat (electrical and mechanical) can be dissipated into the surface area of the motor housing.
Advantages of Permanent Magnet Motor Technology
Upwing Energy has applied some of the cooling topologies used in the medical and defense industries to downhole applications to minimize heat generation. Permanent magnet (PM) motors are an ideal motor technology because they generate much less heat due to their higher electromagnetic efficiency when compared to induction machines, which require an iso-induced magnetic field in the rotor. In addition, PM motors can operate with very large air/fluid gaps between the motor stator and rotor, minimizing fluid friction losses and allowing for the hermetic enclosure of the motor components.
For the Upwing Subsurface Compressor System™ (SCS), the motor section is completely sealed from the pressurized produced fluids and torque is transferred through the magnetic coupling. This topology eliminates the fluid friction losses between the motor rotor and pressurized produced fluids by over 95%, therefore cooling is only required for the electromagnetic losses in the stator.
Innovative Motor Topology for Liquid Pumping
For the Upwing Magnetic Drive System™ (MDS), the required horsepower and associated heat transfer are significantly higher than SCS due to the liquid pumping application (i.e. over 1,000 HP for offshore pumps). Upwing has leveraged its PM motor by providing significantly higher surface area for the production fluid to flow through and carry the heat away from the MDS. The fluid has multiple flow paths inside the motor (around and inside the motor rotor, as well as inside and outside of the stator) to come in direct contact with the sleeved and protected motor components to remove heat. This innovative motor topology for downhole rotating devices enables Upwing PM motors to dissipate three to five times more heat vs. conventional ESP motors. In addition to eliminating the oil-filled, temperature-limited motor chamber and providing universal PM capabilities, the Upwing motor delivers roughly five times the power density of conventional induction motors, which are utilized in ESP applications currently.
Cutaway of the Upwing Magnetic Drive System (MDS) with a flow through motor for enhanced cooling
Retrievability via Slickline
Well intervention using a workover rig is costly. Depending on the fields and geographical areas, the cost of deploying a rig for any operation in some parts of the world and especially offshore can be astronomical. In addition, the loss of production while waiting for a rig and during the workover process, and the opportunity cost of moving a rig away from other operations, significantly adds to the real cost of intervention, and is sometimes overlooked.
Although making subsurface tools reliable and operational in a wide range of conditions should be the primary objectives of operators and tool makers, the second priority should be a fast and cost-effective workover if and when intervention is necessary due to tool failures or well production changes.
Wireline and slickline retrievability is becoming more and more desirable as the industry has developed tools and processes to conduct such retrievals of artificial lift equipment in a matter of hours for onshore, offshore and subsea wells.
Higher Reliability + Easier Retrievability
Upwing Energy has not only increased the reliability of the electrical system of electric submersible pumps (ESPs) via its Magnetic Drive System (MDS)™, but also has integrated easier retrievability in case intervention is required. The mechanical section of the pump driven by the MDS is located on a retrievable string and has zero electrical or mechanical connections to the permanent completion, allowing for fast and inexpensive slickline workovers that do not require specially trained service personnel. The mechanical string is substantially shorter than conventional ESPs, making live well intervention possible, and also allowing for less expensive tool replacement over time. Since all of the electrical components, wires, connectors, penetrators, etc., are a part of the permanent completion, they do not come into contact with the mechanical components that are being retrieved.
Change Hydraulic Sections as Well Conditions Change
Due to the ease of retrievability, hydraulic sections on the mechanical string can be changed out as operating conditions change, ensuring the most optimal and efficient performance at any given time in the well’s life cycle.
The Upwing MDS allows for a single completion for the life of the well regardless of the type of pump that will be utilized downhole.
Permanent Magnet Motor as Magnetic Coupling
As proven in many different applications, permanent magnet (PM) motors have advantages over other motors with regards to power density, efficiency and unity power factor. Furthermore, the large operating gaps between the rotor and stator enable the rotor and the stator to be canned separately, which is widely done for top side applications. This unique capability is even further exploited and leveraged at Upwing through the patented Magnetic Drive System™ (MDS) concept, which utilizes the PM motor as a magnetic coupling.
In the MDS, the stator is canned and positioned as a part of the permanent completion, thereby allowing the rotor and all other rotating components of the pump to be retrieved independently from the stator. This utilization of the PM motor as a magnetic coupling that can be separated/retrieved via a slick line without any connections between the rotating and stationary components offers a protector-less motor/coupling that increases the reliability and retrievability of the system.
Removing the protector section of a conventional electric submersible pump (ESP) system has been a top desire of the artificial lift industry. Upwing Energy is able to not only remove the most unreliable component of an ESP system, the “protector,” but also has introduced an integrated PM motor and magnetic coupling that can be retrieved via slick line, increasing reliability while decreasing part count and costs of all rotating downhole artificial lift equipment.