Fundamentals of coiled tubing operations/technology

1.coiled tubing technology

CoiledTubing (CT) is a kind of continuous tubing of required length that can be wound on a roller. Tubing diameters are typically 0.75 “-5” and steel yield strengths range from 55,000 psi to 120,000 psi. At present, the longest tubing wound by a single drum in commercial use is more than 9000 meters.coiled tubing operations

2, the main components of coiled tubing equipment

• 1) Drum: storage and delivery of coiled tubing;
• 2) Injector head: provides power to run coiled tubing;
• 3) Operation room: Equipment operators monitor and control coiled tubing here;
• 4) Power group: hydraulic power source required for operation of coiled tubing equipment;
• 5) Well control device: wellhead safety device for coiled tubing with pressure operation.    

3. Well control device

Well control is another critical component of coiled tubing operation. A typical coiled tubing well control device consists of a BOP stack (BOP) and a BOP box attached to the upper part of the BOP. (High-pressure connection tubing operations usually have two BOP boxes and a backup BOP.) All these devices must be operated in the field with respect to their pressure levels and suitable temperature ranges.

The BOP box contains a sealing element that isolates the pressure system in the wellbore. It is usually installed between the BOP and the injector head. The BOP box is sealing in either dynamic or static form. The BOP unit is designing as a side door to allow the coiling tubing to replace its sealing elements while in the well.

The BOP is attached to the lower end of the BOP box and can also be used to control wellbore pressure. For coiled tubing operation, the BOP is typically designing specifically to include several pairs of RAMS, each with a specific function. The four-gate system is the most common BOP in operation.

4. Coiled tubing operation characteristics

• 1) No kill operation
• 2) Do not move the pipe string in the well to protect the production tubing
• 3) Able to complete some operations that cannot be carriing out by conventional methods
• 4) Replace some routine operations, with higher efficiency and quality
• 5) Cost saving, simple time saving, safe and reliable, widely used

5. Coiled tubing development

 The coiled tubing applications began in 1944 during World War II, with the subsea line (PLUTO) transporting fuel to Allied forces on the continent.

In the early 1960s, it began to be used in the petroleum industry, mainly for well washing and sand bridge removal. Coiled tubing was on the verge of death due to frequent mechanical accidents.

In the 1980s, technicians improved CT welding and wellhead control systems. Coiled tubing technology has been widely used in workover, completion, drilling, logging and so on. In particular, coiled tubing fracturing has become more widely used in shale gas projects since 2014.