Prudhoe Bay Alaska is a mature oilfield where coiled tubing (CT) drilled sidetracks are the preferred method for gaining access to small reserves. For the CT drilling provider, and ultimately the client, the cost of the CT is a significant component of the overall operational cost and increasing the life of the working CT directly impacts operational economics.

A primary contributor to CT fatigue is plastic deformation. This occurs when the CT is spooled on and off the reel and also when it passes through the injector head. Both these events subject the CT to bending stress and any attempt to reduce the number of such cycles will increase the CT life. Particular operations such as window milling, stuck coil, drilling in open hole require the CT to be moved short distances in and out of the well which increase the number of CT fatigue cycles.

The Short-Trip Module (STM) has been developed to minimize fatigue peaks during these short movements. The system allows small (maximum 20 ft) CT movements in and out of the well without the need to turn the CT reel. This is done by keeping the CT reel stationary and letting the CT, between the reel and injector head, form a natural parabolic arch. Depending on the circulating pressure and CT movement schedule the fatigue can be reduced over 50% in CT fatigue life prediction model.

This paper will detail the theory and design of the STM as well as the issues of its integration onto a CT drilling unit.

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