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CT control and monitoring equipment
Equipment for monitoring and control are important elements of any coiled tubing unit.
The control-console design for the coiled-tubing (CT) unit may vary with manufacturers, but normally, all controls are positioned on one remote console panel. A diagram of a typical well-intervention unit control panel is seen in Fig. 1. The console assembly is complete with all controls and gauges required to operate and monitor all of the components in use and may be skid-mounted for offshore use or permanently mounted as with the land units. The skid-mounted console may be placed where needed at the wellsite as desired by the operator. The reel and injector motors are activated from the control panel through valves that determine the direction of tubing motion and operating speed. Also located on the console are the control systems that regulate the pressure for the drive chain, stripper assembly, and various well-control components.
Equipment parameters to monitor
The coiled-tubing (CT) equipment-related parameters that should be monitored to ensure the equipment is functioning correctly include:
- Traction force
- Chain tension
- Well-control system hydraulic pressure
- Reel motor pressure
- Injector motor pressure
- Stripper hydraulic pressure
The critical job parameters that must be monitored throughout the job are discussed next.
Load may be defined as the tensile or compressive force in the CT just above the stripper and is one of the most important measurements needed for proper operation of the prescribed service. Load may be affected by several parameters other than the hang weight of the CT and include:
- Wellhead pressure
- Stripper friction
- Reel back tension
- The density of the fluids inside and outside the tubing
Load should be measured directly using a load cell that measures the tensile and compressive forces applied to the CT by the injector. A secondary load measurement may be obtained indirectly by measuring the hydraulic pressure applied to the injector motors where the specified hydraulic pressure-to-load ratio is known.
Measured depth is the length of CT deployed through the injector. Measured depth may be significantly different from the actual depth of the CT in the well because of:
- Thermal expansion
- Mechanical elongation
Measured depth can be directly observed at several places on a CT unit using a friction-type wheel that contacts the tubing. Measured depth may also be obtained indirectly by measuring the rotation of the injector shafts. A CT unit should not be operated without a dedicated depth measurement system being displayed to the CT operator. Measured depth should be recorded as a function of time and in relation to internal pressure applied to the CT string for use in bend-cycle fatigue calculations.
Speed may be calculated from the change in measured depth over a specified time period.
CT inlet pressure
Pumping pressure at the inlet to the CT should be monitored and displayed to the CT operator, as well as recorded for use in bend-cycle fatigue calculations or for post-job reviews. This pressure-measurement system must incorporate a method of isolating the pumped-fluid circuit, eliminating the possibility for pumped fluid to discharge into the control cabin if gauge failure occurs. It is recommended that a pressure recorder be incorporated in the CT pressure-monitoring package to record pump pressure throughout the prescribed service.
Well pressure around the outside of the CT at the wellhead should be monitored and displayed to the CT operator, as well as recorded for use in post-job reviews. This pressure-measurement system must incorporate a method of isolating the wellbore fluid circuit, eliminating the possibility for well fluids to discharge into the control cabin if gauge failure occurs. It is recommended that a pressure recorder be incorporated in the CT pressure-monitoring package to record well pressure throughout the prescribed service.
Noteworthy papers in OnePetro
R. Burgos, R. Mallalieu, and K. Wicaksono 2009. Safer, Faster, and More-Reliable Operations With Next-Generation Offshore Coiled Tubing Unit, SPE/ICoTA Coiled Tubing & Well Intervention Conference and Exhibition, 31 March-1 April 2009. 121678-MS. http://dx.doi.org/10.2118/121678-MS
Patrick M.A 1998. Remote Coiled Tubing Operation Monitoring, SPE/ICoTA Coiled Tubing Roundtable, 15-16 March 1998. 46038-MS. http://dx.doi.org/10.2118/46038-MS