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Heavy lifting, Part 2

Published by
Oilfield Technology,

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

Technical solutions

The artificial lift industry has a long history of technical development; however, significant step changes are infrequent. In contrast, permanent magnet motor (PMM) and transmission technology has made significant advances in the past twenty years, driven predominantly by significant increases in magnet material performance to enable smaller machines with high power density.

Time has been spent developing artificial lift methods based on these advances and a portfolio of associated patents. They are specifically focused on novel downhole pumping systems for gas well deliquification, conventional oil and heavy oil applications.

On completion of these programmes, the innovative solutions will enable downhole pumping systems to be deployed where they presently cannot.

Zilift is currently developing three products: TorqueDrive, targeting heavy oil production and gas well deliquification including conventional and unconventional gas wells; SpeedDrive, targeting retrofit conventional oil wells; and a TorqueDrive derivative product specifically targeting well kick starting, for kill fluid displacement as an alternative to coil tubing/nitrogen lift.

These systems negate the visual impact and hydrocarbon leakage present with systems such as pump-jacks and other rod based pumping solutions.

Looking at PMMS

PMMs offer advantages over conventional induction motors due to their greater power within a given space envelope, their ability to run at high speed and with lower power consumption. PMMs also bring the advantages of affordable downhole electrical pumping technology –pump placement and drive delivered reliably downhole – to artificial lift applications where some or all of the following attributes apply: through tubing, slim bore, high solids, deviated or horizontal wells. This will go some way towards:

  • Reducing lifetime lifting costs
  • Extending economic production life
  • Produce with high sand or solid content
  • Produce the reservoir more steadily for longer

These diminutive products allow them to be deployed though-tubing on their power cable, resulting in a more cost-effective solution than conventional ESP deployment, which necessitates a full workover including withdrawal of all the production tubing within the well. It has also been recognised that in certain parts of the world, namely North America where rig rates are low, the full benefit of a through-tubing solution may not be strong, so it also offers jointed tubing variants.

PCPs have traditionally been driven from the surface via a rod system. This approach is effective but has a number of significant drawbacks including inherent power inefficiency, diminishing returns based on the depth of the well, pump placement compromises, monitoring challenges, pump operating window compromises, failures due to friction and rod separation, environmental impact of hydrocarbons at surface, noise, visual pollution, etc.

However, it is now possible to deploy a PCP and remove the compromises and failure modes associated with top drive systems. New tools such as TorqueDrive will have the ability to deliver power directly to the PCP downhole utilising efficient permanent magnetic motors and the innovative Zilift Torque Converter.

The Zilift Torque Converter achieves torque multiplication without contacting parts by focusing internal magnetic fields on the shaft to eliminate meshing mechanical gears. This permanent magnet torque conversion technology combined with PMM and a variable frequency drive (VFD) delivers an efficient, compact, power dense and variable speed machine with inherent overload protection built in. The benefit of this speed reduction and torque multiplication is to enable the PMM to run efficiently at higher speed while delivering an appropriate speed and torque to the (lower speed) PCP.

This technology will be the most significant advancement in downhole electrical machine design for thirty years as, following three years of intensive R&D, prototyping and testing, the TorqueDrive downhole drive PMM PCP system is undergoing qualification testing and field trials this year.

Part 3 of this article can be reached here.

Part 1 of this article can be reached here.

Adapted by David Bizley

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