Even though Permanent Magnet Motors (PMMs) were introduced to Artificial Lift applications more than a decade ago, they can still be considered an emerging technology as the market remains dominated by Induction Motors (IMs). As documented in many previous papers, PMMs certainly bring efficiency advantages. However, the industry needs to first implement critical changes in field operations to ensure the safety of field personnel. At this time, little has been written about their safety implications in the field.
The analysis presented in this paper is supported by safety risk assessments and engineering validation tests conducted in early PMM design stages, discussion with internal and external professionals as well as experts from diverse disciplines such as operations, research, electrical, hydraulic, mechanical, application engineering. It is additionally proven by field experience throughout the Western hemisphere. Based on the findings, the authors can acknowledge that PMMs introduce unique electrical hazards to field operations that may not be obvious or easily identified by field personnel mostly familiar with induction motors.
The purpose of this document is to describe the reasons and circumstances under which PMMs could cause unusual electrical hazards even when the system is powered off or disconnected from electrical sources. This is the case when making electrical connections during installation and pulling or when monitoring electrical parameters during run-in-hole (RIH) and pull-out-of-hole (POOH) activities.
When a PMM is subject to mechanical rotation while being powered off or disconnected from the power source, the internal magnets will move relative to the windings and behave as an electrical generator. Most artificial lift applications have the motor mechanically coupled to the pump(s) and electrically connected to the power cable. Thus, artificial lift systems including PMMs will generate electrical energy anytime that sufficient fluid flows through the pump to force rotation. Unlike applications with IMs, when a PMM downhole system rotates (regardless of rotation direction), it will energize the power cable handled on surface.
If field personnel are not aware of this characteristic of PMMs, they may wrongly think that the system is electrically safe while being shutoff or disconnected from electrical power. This unexpected behavior of PMM systems should be communicated to all field personnel for them to understand that the regular steps used for IMs are not safe for PMMs.
Every field operation requires the participation of multiple parties including operators and service companies. Each involved party should ensure that all field personnel are fully aligned to the specific PMM safety risks and controls. They should coordinate efforts to communicate hazards prior to starting PMM operations and to strictly follow Management of Change (MOC) procedures when required.
The ultimate intention of the authors is to share recommended safety controls already validated in engineering testing labs and in the field to ensure safe operations with PMMs. We invite the industry to join our efforts and work together in the prevention of safety incidents as this innovative technology quickly expands globally within Artificial Lift.