Coiled Tubing (CT) is used as a primary well intervention methodology and is routinely deployed offshore and in onshore land based operations.
Originally constructed from small bore, welded pipework its original applications were somewhat restricted, limited by the coil’s mechanical properties of the day. However, coiled tubing manufacturing and the associated quality control process have radically evolved over time and, in turn, so has CT’s reliability and operational capability. Today, the standard OD sizes of coil tubing that are used in North Sea applications range from 1-in to 2-3/8-in. Large bore 2-5/8-in - 3-1/2-in CT are also routinely deployed in common intervention activities. However, larger, 4.5” - 6” bespoke coil strings have been manufactured for specialist applications.
CT undertakes very similar operations to wireline but has the added benefit of being able to pump fluids and or gas as required and, in negotiating high angle or horizontal well paths. CT excels in areas such as milling/chemical treatments (including acidizing & fracturing) and sand/scale cleanouts.
A three notable features in the evolution of coiled tubing are
- its crossover over into and in undertaking drilling operations including underbalanced or managed pressure drilling (UBD/MPD) where, as a live well intervention, CT’s closed pressure loop is ideally suited.
- The development of strings which can operate in deeper wells with high pressures and temperatures.
- Combination with reliable real-time data services via improvements in telemetry, tooling and computing have widened the application possible with CT.
In terms of offshore application, limitations in using CT are generally governed by the host platform or rig and they are in relation to weights / offshore crane capacity or deck space.
- 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'
- Tubing connector - to allow connection of down hole tools to the coil
Download PDF: Introduction to Coiled Tubing