This paper discusses the prejob research and eventual use of a hydraulic workover (HWO)/snubbing unit for a subsea flowline intervention at the Nansen Spar in the Gulf of Mexico (GOM). Located in a water depth of 3,670 ft (1119 m), the Nansen Spar has been in production since 2002 (Fig. 1). In 2005, a number of umbilical lines became plugged, preventing further chemical injection to prohibit hydrate and paraffin buildup. In 2009, a hydrate blockage formed in a production flowline during the course of an unplanned shut in. Initially, it was decided to perform a coiled tubing (CT) intervention to enter the flexible riser and flowline, clean out the paraffin, and remove the hydrate deposit. During the CT intervention, the pipe became stuck, thereby requiring a fishing operation. At that time, the decision was made to use a 340K hydraulic HWO/snubbing unit to fish the CT and clean out the remaining paraffin and hydrate bridges. The execution and outcome of the fishing and cleanout operation are discussed, as well as some of the challenges associated with not only working in deep water, but through a flexible riser as well. Recommendations based on the lessons learned during the planning and execution of the operation are also presented.

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