Aerospace reliability extended to hydraulic downhole controls

Controlling production sleeves in oil producing conditions downhole is a high reliability task in an unforgiving environment.

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Controlling production sleeves in oil producing conditions downhole is a high reliability task in an unforgiving environment. These are different conditions than those required of military aircraft, a primary business line of Saab Avionics, but the reliability processes must be the same.

Using hydraulics originally developed for the Gripen military air combat jet, Saab, in a joint venture with Triangle Equipment AS and Expro North Sea, developed a new generation inflow control system called NESCOS (non-electrical surface control system) for use in oil and gas wells.

The heart of the system is a high torque hydraulic actuator controlling the all-metal-to-metal rotating sleeve. The sleeve is used to control oil and gas production from separate production zones by using a "chording" principle. Pressure from different hydraulic lines can control multiple zones within a single wellbore. By using the system, the well can be optimized for maximum production and hydrocarbon recovery during the lifetime of the well. The system consists of separate modular units integrated into a compact and easily installed system including:

  • Sleeve unit - controls the production from an individual production zone
  • Hydraulic actuator - transforms hydraulic power into high torque rotation to operate the sleeve unit
  • Hydraulic logic unit - decodes control line pressures to operate the dedicated sleeve
  • Displacement pump unit - operates the rotation sleeve in a stepwise fashion
  • Packer actuation unit - sets zone isolation packers or production packers individually
  • Zone isolation packer - seals between different production zones
  • Production packer - seals between the reservoir and the upper well components
  • Mechanical shifting tool - used to operate mechanically operated sleeves or serves as a backup to the hydraulic control system.

Multiple sleeves

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The NESCOS rotating sleeve system consists of several modular components, five meters in total length, excluding the required packers.
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Depending on the well, up to ten sleeves can be controlled within one wellbore. Sleeves require 30-60 seconds for full closure. The rotational sleeve design is concentric with a market-leading interior diameter of 3.5 in. and an outside diameter of 5.8 in. The sleeve system is modular and the total length, including two packers, is 10 meters. The sleeve units can be mechanically activated if the hydraulic logic unit fails. The sealing area of the inflow sleeves is made of tungsten carbide to improve wear resistance and prevent scale damage to seal surfaces.

NESCOS is assembled by Saab Avionics according to standards comparable with aircraft quality. The system is designed with a 15-year life expectancy. Compared to the sliding sleeve principle, routine maintenance is modest, requiring minimum cycling and an annual exchange of hydraulic fluid for the system to remain in top condition. The system is presently at Rogalands-forskning for testing, and is expected to be fully qualified by the time this is published.

For more information, contact Anders Ekelund, Saab Avionics, tel: +46 70 671 79 72, fax: +46 36 19 41 03, E-mail: anders.ekelund@avionics.saab.se.

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