The coiled tubing unit is a portable, hydraulically-powered service system designed to run and retrieve a continuous string of tubing concentric to larger ID production pipe or casing strings. The basic coiled tubing unit components are as follows:
- Tubing injector head
- Coiled tubing reel
- Wellhead blowout preventer stack
- Hydraulic power~drive unit
- Control cousole.
A simplified c9,iled tubing unit is shown in Fig. C1.
Tubing injector heads
They are designed to perform three basic functions:
- Provide the thrust to snub tubing into the well against pressure or to overcome wellbore friction.
- Control the rate of tubing entry into the well under various well conditions.
- Support the full suspended tubIng weigli; altd accelerate it to operating speed when extracting it from the well.
Figure C2 illustrates a simplified coiled tubing injector head rig-up and wellhead blowout preventer stack.
Coiled tubing reel
It is a manufactured steel spool. Spooled pipe capacities are contingent on the core diameter (Fig. CI).
Reel rotation is controlled by a hydraulic motor that is mounted for direct drive on the reel shaft or operated by a chain~and-sprocket drive assembly. This motor is used to maintain a constant pull on the tubing aud keep the pipe wrapped tightly on the reel.
The tubing is guided onto the spool through a mechanism called the "level-wind assembly" to properly align the pipe as it is wrapped on or spooled off the reel.
Wellhead blowout preventer stack
The BOP stack is comppsed offour hydraulically-operated rams, generally rated for a minimum working pressure of70 MPa (10 000 psi).
The four BOP compartments are equipped (from top down) with:
- (a) Blind rams
- (b) Tubing shear rams
- (c) Slip rams
- (d) Pipe rams
Hydraulic po~er.drive units
They are sized to operate all ofthe coiled tubing unit components. The prime mover assembly size will vary with hydraulic-drive unit needs.
The console includes all of the controls and gauges required to operate and monitor the coiled tubing unit components:
- (a) Red and injector heads are activated through valves that determirre-tubing motion direction at operating speed.
- (b) Control system regulate the drive chain, stripper rubber, and blowout preventers.