Abstract
Coiled tubing is being widely used as temporary or permanent production strings. The installation of a continuous string into a well reduces or eliminates threaded connections thereby minimising potential for leaks. It can be installed in live wells and the insertion or retrieval is generally faster than with jointed pipe.
Future applications of flush, continuous, single-flow pipe in for example slender well designs, all require a good field method of joining pipe sections, which will not compromise material properties or string integrity. The Big Loop method will also overcome the transport weight limitations associated with long and/or large diameter coiled tubing reels.
Considering that the entire pipe handling, connection and well insertion process can be conducted without the use of a rig, there are considerable incentives to use the Big Loop system on offshore installations.
This paper deals with a new concept where a complete continuous string, including subassemblies, can be pre-manufactured on site, tested and subsequently installed once the well becomes available. The connection time is taken out of the critical path of the construction or intervention process of the well.
The concept applies civil engineering pipe upto 7" body OD, which allows the selection of the optimum pipe size required for a particular well.
The pipe is orbital welded and spooled into a free-standing spiral using a bending machine. Plastic deformation is generally less than with general coiled tubing strings on reels. During installation of the string a straightener in combination with conventional coiled tubing or snubbing equipment is used.
To date, two strings have been successfully premanufactured, tested and installed. Further developments are aiming at corrosion resistant alloys, cladded pipe and continuous pumping capabilities during insertion.
