In response to growing concerns related to the future of energy production and climate change, governments in general have deployed plans for reducing their carbon footprints in their countries of operation, featuring increased interests in preserving the ecosystem. These plans include, among other initiatives, the implementation of more energy-efficient technologies across different industries—within which the oil and gas (O&G) sector is already leading a number of sustainability projects that have had an impact on short- and long-term exploration and production techniques.
The production segment has revolutionized the concept of efficiency in artificial lift systems (ALS) during the last 10 years, as it adapts horizontally to different types of lift currently used to extract fluids to surface. A recent ALS motor technology advancement, the permanent magnet motor (PMM), has proven to contribute to streamlining operations and delivering significant energy savings. This article will establish the main differences between PMMs and traditional induction motors (IMs). It will explore a case study that showcases improvements on lift efficiency and demonstrates how other collateral aspects were a direct result of the implementation of this technology—including reduced maintenance, flow assurance, and more.
Powerful magnets overtake conventional induction motors. One of the constant requests from O&G is the deployment of technologies that maximize production and reduce operational costs. ALS service companies have mainly been working on the development of new products to ultimately increase production. These primarily include reductions of operational costs, due to the combined effects of high oil prices with accelerated exploration and production campaigns, leading to the postponement of research and development agendas. Since 2015, instability and extended low oil prices did not support major R&D investments and instead promoted the focus on technologies offering greater efficiencies and the ever desirable “lower operations costs.”
More recently, higher oil prices, combined with established environmental, social and governance policies, are proving to be the perfect coalition where ALS service companies and operators can make the big jump to develop and deploy more efficient solutions. Existent, proven technology was identified as an opportunity to design a unique line of higher-efficiency drive-head units for progressing cavity pumping (PCP) systems.
PMM technology is based on the use of rare-earth permanent magnets that create a continuous magnetic field. The rare-earth minerals include 17 metallic elements with unusual fluorescent, conductive and magnetic properties, making them useful when alloyed or mixed in small quantities with more common metals, such as iron.1 Neodymium (Nd) is one of these rare-earth elements, and since the 1980s has been combined with nickel to manufacture hybrid batteries. These batteries can be recharged repeatedly while holding a significant energy relative to their volume (size). As of today, Nd is well known as one of the strongest permanent magnets in the market and has been utilized in portable electronics, hybrid cars, speaker systems, and wind-turbine motors. Because of its magnetic properties, Nd has been incorporated into electric motor designs to improve energy and transmission efficiency while in operation.
Conventional PCP drive-head units are traditionally driven by electric induction motors (IMs), which operate at high rotational speeds and have two main components—the stator and rotor. The stator is an outer, non-moving chamber that creates a magnetic force through alternating current that “induces” the rotor to spin. The stator has a cylinder shape formed by a ring of electromagnets, slotted steel, and iron layers. Copper wire is wound through the cylinder’s interior, creating the magnetic poles. The rotor consists of a group of electromagnets, arranged around a cylinder, that rotates, due to the magnetic field produced by the stator.2
These motors are typically combined with belts and sheaved transmission systems that operate within a specified speed range. Unfortunately, the transmission from the electric motors to a PCP drive head—through the belts and sheaves up to the polished rod—is inefficient. This creates significant energy losses, resulting in a deficit waste of electrical energy. Since 2008, several electric motor manufacturers have embarked on a journey to optimize the transmission of rotating energy from the electric motor to the system. It is also well known that by using a direct-drive head system, transmission losses are reduced enormously in a rotational machine. Concurrently, this also creates challenging conditions, such as having drive-head units strong enough to hold their integrity while operating at higher speeds. Then, on the lower end, this, in turn, requires an increased capability from the electric motor to supply higher torque outputs.
No transmission, more power transfers. The PMM is a technology that simply modifies the widely used IM. PMM designs include the same components, such as the rotor and stator. However, in the PMM, the rotor can be a solid piece, featuring small sections of Nd encased on the rotor surface,3 Fig. 1.
Nd sections in the PMMs are permanently magnetized, eliminating the requirement to inject large amounts of current required to create the magnetic field between the rotor and the stator, as with all traditional IMs. With a more magnetic material in the rotor, slippage in the PMM motor is eliminated. This helps to reach higher efficiencies in the system, starting at 94%. As a result of these modifications on the rotor’s raw material, the electric motor offers higher torque at significantly lower speeds.
Through this achievement, the transmission system (belts, pulleys, and gear reducers) is eliminated from the supplemental components required by the electric motor, Fig. 2. This indirectly reduces more than 50% of the inefficiencies of the electric motor when transmitting speed, torque and power to the PCP drive head while in operation. Because of the sheave-less condition, the equipment will also be safer, featuring less noise and less carbon footprint throughout its operational life.
Perfect fit for oil and gas wells. Expanded PMM development brought several re-evaluations of IM performance, based on parameters such as power factor (PF), efficiency (Eff), current and how these parameters depend on operational speed. Figure 3 shows a comparison between PMM and IM parameters. The key findings are: 1) PMM PF is substantially greater than IM PF across the load percentage curves; 2) PMM Eff is generally greater than IM Eff. When operating at lower speeds, IMs need double operational speeds to reach the efficiency of PMMs; and 3) PMMs need less current to offer a higher efficient performance over IMs. IMs require higher currents, leading to increased energy consumption.
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