ABB Breaks Ground in Artificial Lifts With New Generation of Rod Pump Control Technology; Controller Achieves Dramatic Increases in Well Efficiency, Production And Rod-stress Reduction

Erik Torseke, Vice President of Pumping Artificial Lift Products, ABB Inc., Automation Technologies

ABB Inc., the world's largest Variable Speed Drive (VSD) manufacturer, decided in mid-2001 to develop a state-of-the-art Rod Pump Controller, following rigorous activity in the upstream part of the oil industry that included development and introductions of products/solutions for Electro Submersible (ESP) and Progressing Cavity Pumps (PCP).

"This commitment resulted from the growing realization that the control of rod pumps had fallen behind the technology used for ESP and PCP applications," according to Tim Gladd, North America business manager for ABB's Pumping Artificial Lifts Products (PALP). ABB's view, domestically and globally, was that the standard Pump-Off Controller, either as a stand-alone unit or in combination with a Variable Speed Drive, did not give users full benefits, he said. "This was not an outsider's view but, rather, the view of seeing electrical control at work in a host of fellow industries, and realizing that opportunity abounds for this specific application – and that it could benefit the entire Oil industry worldwide."

The opportunity? -- creating a new product/control solution that would combine the latest in power electronics technology with an up-to-date operator interface.

Leverage Experience, Youth and Encoder-less Control

The R&D project deliberately combined 25 years of corporate Rod Pump field experience, young software engineers and power electronics experts. The assignment: Optimization of a Rod Pump's inherent capabilities.

The team's project code became "Pump-On Controller," an ironic twist on the fact that the ALC 600 standard artificial lift controller ABB created "never allows the pump to pump off," according to senior application engineer Jim Settersten, who was part of the software development team.

The team recognized early on, Settersten said, that the key to optimising a rod pump's capabilities on any oil field anywhere in the world hinged on accurate rod speed control. That capability ABB already owned via a patented DTCTM (Direct Torque Control) that is able to provide the necessary speed control without the use of encoder feedback. The DTC feature could enable the motor drive to calculate the state (torque and flux) of the pump load 40,000 times per second, making the drive virtually trip-less. And DTCTM also provides extremely accurate rod- position calculations with only the use of a single proximity switch.

Motor Control in All Conditions Breaks New Ground, Too

The team also took head on the historical problem of VSD control of rod pump motors: the inability to control motor speed when the motor is generating. Ignoring the problem – and the rod stress that results from it – was out of the question; as was the traditional solution of incorporating braking resistors into the control design. (Braking resistors, while providing the necessary motor control, both take up unnecessary space and generate heat.)

"We harnessed and married in additional technology at our fingertips -- an active front-end-equipped VSD," explains Brian Glisch who was leading the team's hardware development. "That type of motor controller construction not only provides us with the accurate speed control but it also feeds the generated power back into the network; which means all of the energy regenerated from the motor is utilized – fed back to the utility." This type of "demand side management" results in significant reduced energy consumption, and shortens further payback on rod pump controller investments.

An additional, though unintended, benefit gained from utilization of this type of regenerative VFD emerged, too. The drive's front end acts as an active harmonics filter, ensuring harmonics content that is less than 3%. "Regular drives can often generate up 30% harmonics content, forcing the user to invest in expensive harmonics mitigation equipment," according to Glisch. The unique LCL filter in the AC drive the team utilized is active and shapes the current sinusoidally. This prevents harmonic distortion that is the bane of the power supplier to a given pump or field of pumps.

Enclosures and Controllers Designed to Operate in All Climes

With the speed control problem solved, the team set out to develop an enclosure that would allow for continuous operation in temperatures ranging from -58 to +122˚F (-50 to +50˚C). Drawing from ABB's experience in delivering over 5,000 outdoor enclosures to the oil industry, the team wanted a design that would protect and keep the vital electronics cool and operating in the most adverse environments around the globe.

"It does not matter how good your product is if it can't withstand the environment – both nature and the often rugged and hostile operating conditions," observes Rick Jasinski, operations manager for ABB Drives, Motors and Machines. "We designed the enclosures on the premise that you get only one chance out in the field, so we had to get it right the first time." The specification called for forced-air cooling, without the use of an air filter. Solution? In this instance, adapt technology based on the same technology used in central vacuum cleaner systems: the enclosure design channels clean air through the heat sink, while dust and larger particles end up in a separate compartment that can be cleaned out. "The design was tested in West Texas dust storms and it works flawlessly," Jasinski said.

Well Performance and Operation – From the Truck!

A quantum leap in new operator interface design includes replacement of traditional Pump Off Controller's (and their hard-to-read, monochrome, small displays) with a 10-inch color LCD display designed for outdoor use. It is readable at a distance of 30 feet (10m), even in bright sunlight. The interface works with standard Flash Memory cards like those used in digital cameras – the perfect complement for the advanced functionality of the Rod Pump Controller. (The Controller is also prepared to communicate to SCADA systems.)

"This interface design is very cost efficient and reliable technology and it makes it very easy for us to distribute software upgrades that end users can install quickly and easily," says Jim Settersten. The same software also can be loaded into a portable PC instead of, or as a complement to, the 10-inch display. "Operators love this entire feature, since they can just drive up to the well and sit in the comfort of their truck and view the performance of the well, change parameters or download data into their laptop computer," notes Settersten.

The user interface also automatically saves the five start-up cards and the five shutdown cards. Users also have the ability to individually name and save 48 cards that can be retrieved later or be transferred to a PC as Comma Separated Values (csv) files. Additionally, another 48 cards can be saved automatically at predetermined intervals. A data logging function also allows the user to log, at predetermined intervals as short as every 5 seconds, up to 16 different variables for up to 3,000 values each. "Using such leading-edge technology in conjunction with the flashcard gives us a very flexible and user-friendly operator interface," concludes Settersten. "Operators can learn in seconds what each well is doing, and change it as needed."

Quantum Leaps in Control Strategy Yield Pump Efficiency, Production Increase

As for actual control software, the new ALC 600 controller applies two new, but straightforward, control strategies for Rod Pump Control. The first control strategy -- a patented feature named "Rod Saver" -- allows users to change the speed five times within each stroke; this speed control reduces the stress on the rods. The advanced user interface allows the user to tailor the shape/operation of the dynacard to each well in real-time. Depending on the well, this results in rod load reductions sometimes in excess of 20%.

The team also learned in creating this dynamic operating control that pump efficiency goes up dramatically -- both from better pump filling, and from a longer down-hole pump stroke. Steve Weingarth, manager of the application-engineering group who wrote the software, observes that, "on the way to achieving our primary objective of reducing rod stress, we discovered the positive effect of stress reduction on pump efficiency -- an exciting discovery for the development team, and for the entire Oil industry!"

Retrospectively, the increase in well efficiency resulting from rod-stress reduction is simple and logical to explain: with a tailor made dynacard, the pump gets more time to fill at the top and bottom of the stroke, and the surface unit and pump work in unison, creating a longer down-hole stroke.

The team's second groundbreaking control strategy is the Multi Set-Point Fluid Level Control, using the exact percentage markers provided via the dynacard.
The single set-point control used in POC's was deemed too restrictive to really profit from the advantage of a variable speed drive. Instead, the team came up with a simple, brilliant control strategy that utilizes three set points. The first point is simply used to maintain the fluid level at a predetermined level above the pump. An increase in fluid level prompts a small speed increase/adjustment of the pump, and the opposite if the fluid level goes below the desired level. This ensures a constant low-fluid level that maximizes the inflow from the formation.

The second control point, set slightly to the left of the first, is used to detect fast movements of the fluid level due to gas interference. This control point makes faster speed reductions, ensuring that the pump does not pump off. Similarly, a third control point is set to detect gas or fluid pound. This control point will quickly bring the unit down to minimum speed, and has been proven very useful for wells with gas interference. As the gas hits the pump, the unit slows down instead of stopping the unit like a POC. By moving the pump slowly, the gas gets through more efficiently and the stress is minimized. As soon as the gas interference is mitigated, the ALC 600 controller automatically accelerates to maximum speed and pumps the well down to the required fluid level. And whatever production was lost due to the gas interference is regained by running at a faster speed until the desired fluid level is reached.

These two new control strategies complement each other in a way that was a surprise to the team. The ALC 600 maintains a lower fluid level, and a lower fluid level results in a lower pump intake pressure that, in turn, results in lower pump efficiency. However, the positive effect of the Rod Saver often results in a net improvement of pump efficiency, even though the pump intake pressure is reduced.

Two-year Field-site Testing Documents Dramatic Production, Efficiency, Improvements

ALC 600 rod pump controllers, now in manufacturing production for use in oil fields worldwide, have been installed on wells in the U.S., Mexico and Venezuela. Owners at each of these field sites have seen both dramatic production and efficiency improvements, and reduced rod stress in each and every case. Beginning in 2001, units have been utilized on everything from deep deviated wells in Wyoming and wells with gas interference in West Texas and Mexico, to high-producing wells in Venezuela. The installations have created a lot of interest from oil companies all over the world, with the next round of installations planned for Europe and the Middle East.
Sharing The Technology With The Industry's Future Managers -- Now

"Like all new products/services and their benefits, it takes time for this technology to become widely familiar, comfortable, and accepted – an introductory phase and cycle that is especially true for the U.S. market," observes Gladd. "In addition to working alongside field owners and their production operations, as well as OEMs that serve the industry, ABB is working in close cooperation with universities that offer extensive training and degrees in petroleum engineering," he said.

Texas Tech University in Lubbock, as one example, is installing a unit on their newly developed test well. Such cooperation between manufacturers and university programs creates a win-win for both parties. Universities gain access to leading-edge technology for their test and training wells and research facilities; and manufacturers are able to have students – the industry's future managers – work firsthand with the technology and the operating and energy savings benefits the technology achieves. "These controllers, built around VFD technology that regulates the speed of the pump motors for real-time, real-world conditions, only the energy needed is used. This yields significant energy saving, production increases and reduced maintenance that will continue to pay back long after the equipment cost is recuperated – great modeling for university's future industry managers," is how Chuck Clark, senior vice president of ABB Inc., sums it up. Such cooperative efforts with research-driven programs also create dialogue and interchange of tried-and-true results that often become the catalyst and foundation to/fir the next generation of technology, Clark noted.
Ongoing R&D Commitment Yields Technology, Surprises, That Benefit Producers

Research and development commitments at ABB Inc. exceed some $1.6 billion annually. The development of the ALC 600 Rod Pump Controller is exemplary of how ABB leverages existing expertise to bring new products -- based on new technology – to the market. In this specific case, the development team set out to create a complement to the already successful line of ESP and PCP artificial lift controllers -- and ended up with a product that exceeds the team's most ambitious expectations. The controllers, which have the ability to help producers achieve unprecedented well efficiency, production, and rod-stress reduction, are a testament to the value of continuous investment in research and development.