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Intervention Workover Control Systems (IWOCS) configuration?

asked Jul 27, 2016 in Engineering by PedroGleason (445 points)

Is there an example of the Intervention Workover Control Systems (IWOCS) configuration that someone can share?

1 Answer

+1 vote
answered Jul 27, 2016 by kendrickfeng (745 points) | selected Aug 1, 2016 by odadmin
 
Best answer

IWOCS are complex and varied from one company to another. I would recommend to contact a specific manufacturer and ask them to propose an IWOCS configuration based on your requirements and project’s needs.

You can use the following conditions and requirements when specifying the IWOCS:

  • Moored vessel - time required by the control system to perform the following should be no greater than 120 seconds:
    • Close lower subsea test tree (SSTT) valves
    • Vent cavity between flapper (or ball) valve in lower SSTT and retainer valve
    • Disconnect the SSTT latch
  • Dynamically positioned vessel - time required by the control system to perform the following should be no greater than 15 seconds:
    • Close lower SSTT valves
    • Vent cavity between flapper (or ball) valve in lower SSTT and retainer valve
    • Disconnect the SSTT latch

The control system is composed of all the equipment necessary to control the subsea test tree, the Tubing Hanger Running Tool (THRT) / Cap Tree Running Tool (CTRT), the lubricator valve, and the surface tree.  The components of the control system include, but are not limited to, the following:

  • Hydraulic Power Unit (HPU)
  • Umbilical(s) on powered reel(s) (typically pneumatically-powered)
  • Pneumatic remote control station for umbilical reel operation
  • Hydraulic hoses from HPU to hydraulically-actuated surface tree valves
  • Hydraulic hoses from HPU to lubricator valve (~300 ft )
  • Umbilical junction plates
  • Umbilical clamps (for attachment of umbilical to landing string)
  • Jumper umbilical(s)/hoses from HPU to umbilical reel(s)
  • Downhole hydraulic accumulator assemblies (some systems)
  • Additional electrical equipment for electro-hydraulic systems (some systems)

Umbilical clamps preferably are to be cast or forged steel, and must have no loose components.  All bolting or fastening devices used by the clamps are to be trapped in place, preventing accidental dropping of sub-components in the hole.

A separate control system should be used for the subsea tree, utilizing separate multi-hose umbilical(s) attached along the outside of the marine riser.  To avoid confusion, the umbilical used inside the marine riser to control the SSTT is to be called the "internal IWOCS umbilical" and the umbilical on the outside of the riser is to be called the "external IWOCS umbilical.” 

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