Drilling and workover rigs use a drawworks to pull up on the tubulars deployed into a well. The drawworks is attached to a mast or derrick, which in turn is supported by the ground or a floating vessel. The tubular's weight is not transferred to the wellhead.
Coiled Tubing uses an injector head, instead of a drawworks, to pull and push tubing in and out of a well. The injector is generally mounted directly onto the wellhead, unavoidably transferring some of the reactive loads to the wellhead.
These loads can be very substantial. They not only include the tubing's weight in the well but also loads generated by the Coiled Tubing on surface, that tubing which is being bent and pulled sideways. Often additional support is required to at least partially isolate these loads from the wellhead. This paper identifies the various loads that Coiled Tubing imparts to a wellhead and how support mechanisms provide protection to the wellhead.
General industry practice is to connect Coiled Tubing injectors directly to a wellhead stack. This stack typically includes blow out preventers (BOP's), flow tees and risers, mounted directly on top of a Christmas Tree, a casing flange, a tubing hanger or a drill pipe stub. Connections between the injector and the well itself are generally flanges or some form of quick union.
In the absence of any secondary support device, all the loads applied by the injector to the Coiled Tubing entering or exiting the injector, need to be supported by the wellhead. How the forces applied to the Coiled Tubing are transferred to the wellhead is shown in Figure 1.
Historically, simple chains have been used to anchor the injector, preventing it from moving laterally and thereby bending the wellhead stack. Increasingly, much more rigid frames are being used which are designed to stop the injector moving relative to the wellhead. These frames transmit bending loads to the ground or platform rather than onto the wellhead. This paper will describe how the support systems work and show where the systems do not protect the wellhead.