Coiled tubing is a circular, small diameter, thick cast iron steel, unbraided wire that is used to perform well workover and intervention operations during drilling operations. The diameter of the coiled tubing ranges from 25 mm to 83 mm and is generally rolled upon the spool on a large reel. Coiled tubing is sometimes also used as production tubing in the depleting gas wells.
Coiled tubing is an important tubing application used in the well workover & intervention operations. Coiled tubing is used to carry out operations in the same way as the wireline tubing is used. However, there is an advantage of coiled tubing over wireline tubing. The advantage of using coiled tubing instead of wireline tubing is that the chemicals can be pumped inside the borehole easily through the coiled tubing and the operator has the access to push it via pump whereas if wireline tubing is used, the injected chemicals pass through the tubing because of gravity pull and the injection happens at the slow rate. The coiled tubing operations are carried out by a derrick on the wellhead platform.
Coiled tubing generally consists of gripper blocks, skate rollers and arch rollers. The use of coil tubing is primarily to pump treatment fluids such as injection of chemicals, drilling fluids, etc. Other uses are to fish the lost tools or equipment deep inside the wellbore; taking up and down well logging tools.