Abstract
Composite Coiled Tubing (CCT) is well on its way of becoming a widely accepted alternative to steel CT. Increased corrosion and fatigue resistance combined with a high strength to weight ratio are the main drivers behind these developments. Current CCT applications are limited to service strings and flowlines, however in 1997 Shell International Exploration and Production together with Airborne Development started the development of a thermoplastic composite coiled tubing for drilling purposes. To date, various prototypes have been manufactured and tested for internal pressure, tension, compression, bending, bending fatigue and chemical ageing.
Latest developments aim to embed electric power conductors within the wall thickness of the composite pipe that will enable the use of Electric Drilling Motors, Electric Submersible Pumps and electric tractors. In addition, real-time data transmission is possible by superimposing the data signal onto the power conduit. Such a Power & Data Transmission Composite Coiled Tubing (PDT-CCT) has better hydraulic performance than a CT with internal wireline, and is easier to use from an operational aspect. Coil materials used include advanced thermoplastic matrix materials, glass fibres for strength layers and electric insulation, and carbon fibres to provide strength, stiffness and electrical screening. Furthermore there is the possibility to embed optical fibres to measure temperature, flow and pressure along the complete string length and to monitor the condition of the composite material.
This coil avoids currently encountered problems with thermosetting CCT such as:
Low working temperatures; temperatures in excess of 150°C will be possible with the PDT-CCT
Collapse of thermoplastic liner; the PDT-CCT liner is welded to the structural layers
Unexpected failure; monitoring strain and chemical ageing provides early warning for failure
Low density; the copper conductors increase the coil density to avoid buoyancy induced buckling
Low stiffness; electric or hydraulic tractors along the string length enable Extended Reach CT Drilling