Special care must be taken tomaintain the integrity of the coiled tubing when performing subsea well intervention from a lightvessel without the use of a riser. In these cases the coiled tubingwill act as a riser with respect to withstanding the external loads from waves, current andvessel motions. To avoid local buckling of the coiled tubing as it enters the subsea lubricator it is important to keep the vessel positioned such that the bending of the coiled tubingis kept as small as possible.

This paper will outline a method for estimating the optimal set pointfor the vessel positionduring riser less coiled tubing operations. The method is based on a combination of measurements and analytical methods for description of the structural behaviour of coiled tubing and the subsea stack. The analytical method developed is compared to simulations using commercial riser analyses software.

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