There are three types of conduits used to work in wells including jointed pipe (drill pipe, tubing, casing), cable (wireline, slickline), and continuous pipe (coiled tubing).
Coiled tubing (CT) is typically continuous steel pipe ranging in diameter from 1” OD to 3.5” OD. It is used to perform drilling, completion and intervention functions, though the majority of the CT service are well interventions. A CT “unit” is the term used for the set of equipment used to run the CT in and out of wells.
In North America, most of the CT services are for drilling out frac plugs in wells that have been fractured. This application typically requires 2 3/8”, 2 5/8” or 2 7/8” CT because of the long horizontal wells that contain the frac plugs. The rest of the CT services in North America, and the rest of the world include well cleaning (removing sand or cleaning with acid), matrix stimulation (acidizing top remove skin), and many other applications such as fishing, logging, perforating, removing scale, well drilling, etc. These applications usually use CT in the 1.5” to 2 3/8” range.
Below is a list of the key equipment used in CT applications:
- Reel unit - for storage and transport of coiled tubing
- Injector head assembly - to provide the surface drive force to run and recover the coiled tubing
- Control cabin - from which the CT operator monitors and controls the coiled tubing
- Power pack - to generate hydraulic and pneumatic power required to drive the CT unit
- Pressure Control Equipment including BOPS - to contain well pressure and allow deployment of down hole tools into 'live wells'
- Downhole tools:
- Tubing connector - to allow connection of down hole tools to the CT
- Check valves – to prevent well fluids from flowing up into the CT
- Motor – for drilling applications
- Directional Control Tools – for open hole drilling
- Vibration tools – to reduce friction and allow further penetration in horizontal wells
- Logging and memory tools
- Fishing tools
- Tractors – to pull the CT into horizontal wells