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Coiled tubing is used for a wide variety of oil and gas well interventions. It is used in the completion and production of such oil wells, as well as cleaning and cementing these wells. It can perform open hole drilling operations. Coiled tubing is also used to fracture wells, which is done to break the rock in order to allow the substance in the well to flow. If used properly, coiled tubing can be used for virtually any oil and gas well operation.
The coil looks like a long continuous string of tubing that is coiled and rolled into a spool. It can range in diameter from 8 feet (2.43 meters) to 12 feet (3.6576 meters). Coiled tubing consisting of 26,000 feet (7924.8 meters) of metal piping have been fabricated.
Coiled tubing contains metal string or piping that is generally between 1 inch (2.5 cm) to 3.25 inches (8.3 cm) in diameter. It is made from carbon steel metal piping of a very fine grain size. As the metal piping is coiled, it is welded along its length so that no joints are visible.
The outer diameters of a coil can range from 0.75 inches (1.9 cm) to 4.5 inches (11.4 cm). The bottom of the coil is commonly referred to as the bottom hole assembly (BHA). The size of this bottom tool string can vary greatly, depending on the operation the coiled tubing is being used for.
This product carries out functions similar to wireline, but with added benefits. Wireline is a cabling technology that is also used in oil and gas well intervention. The advantage that coiled tubing has over wireline is the ability to pump chemicals through the coil and to push the coil into the hole, whereas wireline depends on gravity for this function.
In addition, coiled tubing can be a cheaper alternative to conventional drilling string. One reason is that it allows the continuous feeding of the tubing into the hole without constant interruptions. These interruptions are the result of the need to constantly add new drill pipe every time the hole is deepened. Frequent interruptions can prove to be quite time-consuming, and increase the rig time required.
Using coiled tubing can eliminate the drill string-feeding time by being continuously fed, which is a major economic advantage. The need for a lifting device, referred to as a "derrick," can also be eliminated. This can further cut back on price by reducing the hourly cost of the rig.