Coiled tubing

In the oil and gas industry, coiled tubing refers to a long metal pipe, normally 1 to 3.25 in (25 to 83 mm) in diameter which is supplied spooled on a large reel.

For coiled tubing operations on sub-sea wells a mobile offshore drilling unit (MODU) e.g. semi-submersible, drillship etc.

has to be utilized to support all the surface equipment and personnel, whereas wireline can be carried out from a smaller and cheaper intervention vessel.

It can range from something as simple as a jetting nozzle, for jobs involving pumping chemicals or cement through the coil, to a larger string of logging tools, depending on the operations.

The safest (though not the cheapest) solution would be to attempt to circulate out the fluid, using a gas, frequently nitrogen (Often called a 'Nitrogen Kick').

By running coiled tubing into the bottom of the hole and pumping in the gas, the kill fluid can be forced out to production.

Pumping through coiled tubing can also be used for dispersing fluids to a specific location in the well such as for cementing perforations or performing chemical washes of downhole components such as sand screens.

In the former case, coiled tubing is particularly advantageous compared to simply pumping the cement from surface as allowing it to flow through the entire completion could potentially damage important components, such as the downhole safety valve.

The BHA also provides directional survey, gamma, pressure, temperature, and in some cases, petrophysical logs as drilling progresses.

The latest generation of advanced Coiled tubing drilling BHAs offer the ability to steer the bit,[2] enabling the well's trajectory to be corrected in response to the measurements taken by the sensors.

Below the injector is the stripper, which contains rubber pack off elements providing a seal around the tubing to isolate the well's pressure.

[3] A coiled tubing unit (CTU) is a self-contained multi-use machine that can do almost anything that a conventional service rig does - with the exception of tripping jointed pipe.

The advantage of this is less hydraulic pressure and less stress on skate rollers and backing plates increasing the life of the equipment.