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. With Upwing’s hermetically sealed system, downhole environmental changes have no effect on the motor or the bearings.
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.