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Heavy lifting, Part 3

Published by
Oilfield Technology,

Norman Liley, Zilift, UK, examines the growing importance of artificial lift as heavy oil production continues to grow.

Working without workover rigs

Outside of North America, workover rigs are typically in short supply largely due to their focus on drilling operations. A well requiring a replacement of its ESP may have to wait many weeks or months before a workover rig can be scheduled. Therefore conventional ESP failures can result in significant deferred or lost production, which can be avoided with spooled solutions. As mentioned the company has recognised the different landscape within North America with respect to workover rig availability and offers a jointed tubing option.

Now ESPs can be deployed on wireline cable, jointed tubing or coiled tubing as local economics dictate and take all the benefits of a PMM ESP including through tubing deployment, slim yet powerful, high speed artificial lift. The technology also opens up a realistic opportunity for live well intervention and restricted access applications with future developments. As a result, operators will no longer be limited to installation on tubing and can explore the advantages of through tubing deployment including:

  • Reduced life-cycle costs due to greater deployment options and reduction in deferred production.
  • Extend economic production life.
  • Reinstate production without pulling tubing.
  • Access restricted zones.
  • Recover production during primary ESP downtime.
  • Reinstate production following gas lift failure.

Design considerations

For decades ESP technology has been at the forefront of artificial lift in conventional reservoirs with higher flow rates and viscosities of > 18 API.

All ESPs consist of a motor to deliver the power, equaliser to isolate motor and wellbore fluids and centrifugal pump to provide the energy to lift the fluid. Historically ESPs are powered by induction motors.

Zilift’s Equalizer is a seal arrangement consisting of four effective barriers including mechanical seals, a labyrinth and pressure compensation that has been designed to perform in any orientation from vertical to horizontal.

However, fundamental electro-magnetic flux density limitations of induction motors mean that it is difficult to deliver the power required to lift the fluids while scaling down the induction motor to smaller diameters at the same time. Due to the size of induction motor driven ESPs the accepted configuration has always been to mount the pump above the motor, until today.

The company’s chosen configuration is to place the pump section at the lowest point in the string with the motor at the top. Having the pump inlet at the deepest point in the well offers significant benefits for pump filling and gas handling.

It is concluded that permanent magnet materials have advanced considerably over the last ten years making its economic application a reality where space is at a premium. The time is now right for its widespread application within the artificial lift industry. Permanent magnet (PM) is now the technology of choice for today’s leading electrical machine design in applications from automotive, aerospace and defence to wind generation. PMMs are inherently efficient, capable of delivering high power creating optimum power density in the smallest package.

The value proposition of such technology to operators will be realised over the life-cycle of the well in the form of decreased intervention costs, reduced electrical consumption and by a large reduction in deferred or lost production.

Part 1 of this article can be reached here.

Part 2 of this article can be reached here.

Adapted by David Bizley

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