chinalie: Coiled tubing

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Coiled tubing refers to metal piping, normally 1" to 2.875" in diameter, used for interventions in oil and gas wells and sometimes as production tubing in depleted gas wells, which comes spooled on a large reel. Coiled tubing is often used to carry out similar operations as wireline The main benefits over wireline are the ability to pump chemicals through the coil and the ability push it into hole rather than relying on gravity. However, for offshore operations the 'foot print' for a coiled tubing operation is generally larger than a wireline spread, which can limit the number of installations where coiled tubing can be performed and make the operation more costly. A coiled tubing operation is normally performed through the drilling derrick on the platform, which is used to support the surface equipment, although on platforms with no drilling facilities a self supporting tower can be used instead. For coiled tubing operations on sub-sea wells a semi-submersible has to be utilised to support all the surface equipment and personnel, where as wireline can be carried out from a smaller and cheaper intervention vessel. Onshore, they can be run using smaller service rigs, and for light operations a mobile self-contained coiled tubing rig can be used.

The tool string at the bottom of the coil is often called the bottom hole assembly (BHA). 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.

Coil tubing has also been used as a cheaper version of work over operations. Performing open hole drilling and milling operations. It can also be used to fracture the well, a process where fluid is pressurised to thousands of psi on a specific point in a well to literally break the rock apart and allow the flow of product. Coil tubing can perform almost any operation for oil well operations if used correctly.

Contents

1 Uses

1.1 Circulation

1.2 Pumping

1.3 Drilling

1.4 Logging and perforating

1.5 Production

2 Coiled tubing rigup

3 Onshore light coiled tubing unit

4 Major coiled tubing service companies

5 See also

6 External links

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Uses

Circulation

The most popular use for coiled tubing is circulation. A hydrostatic head (a column of fluid in the well bore) may be inhibiting flow of formation fluids due to its weight (the well is said to have been killed). The safest (though not the cheapest) solution would be to attempt to circulate out the fluid using a gas, frequently nitrogen(Often called as a 'Nitrogen Kick'). By running in coiled tubing to the bottom of the hole and pumping in the gas, the kill fluid can be forced out to production. Circulating can also be used to clean out light debris, which may have accumulated in the hole.

Pumping

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 sandscreens. 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.

Drilling

A relatively modern drilling technique involves using coiled tubing instead of conventional drill pipe. This has the advantage of required less effort to trip in and out of the well (the coil can simply be run in and pulled out while drill string must be assembled and dismantled joint by joint while tripping in and out). Additionally, the coiled tubing is stripped into and out of hole, providing a hermetic seal around the coil and, if desired, allowing the well to flow during drilling operations. Instead of rotating the drill bit by using a rotary table or top drive at the surface, it is turned by a downhole motor, powered by the motion of drilling fluid pumped from surface.

Logging and perforating

These tasks are by default the realm of wireline. Because coiled tubing is rigid, it can be pushed into the well from the surface. This is an advantage over wireline, which depends on the weight of the toolstring to be lowered into the well. For highly deviated and horizontal wells, gravity may be insufficient. Roller stem and tractors can often overcome this disadvantage at greatly reduced cost, particularly on small platforms and subsea wells where coiled tubing would require mobilising an expensive mobile drilling rig. The use of coiled tubing for these tasks is usually confined to occasions where it is already on site for another purpose, for example a logging run following a chemical wash.

Production

Coiled tubing is often used as a production string in shallow gas wells that produce some water. The narrow...(and so on)