Flow assurance in subsea production flow lines is becoming more prevalent as deepwater well developments continue to grow. Coiled tubing (CT), though traditionally used in wellbore environments, can be utilized to address flow assurance.

Complications are possible when applying CT technology in a nonconventional environment. Connection tie-ins and available deck area are typically incompatible with intervention-type activities, and challenging issues such as weight limitations, nature of blockage, and weather sensitive environments lead to the need for elaborate planning with multiple contingencies to address the uncertainties. Our study investigated the operational planning and logistical requirements associated with the radiation of the flow assurance for the Serrano flowline.

The Serrano flowline is located in the Gulf of Mexico (GOM), in 3,500 ft of water and is tied back 6 miles to the Auger TLP. Three subsea wells have produced through the electrically heated Serrano flowline since 2001. In November 2006, there was an unplanned shutdown of the flowline and despite numerous attempts to restart, the wells had failed to flow.

In December 2007, after 6 months of intensive and complex planning, a standalone CT operation was successfully performed while drilling operations continued on the main rig. The operations consisted of utilizing a unique small footprint compensation frame to allow access to the flowline from a confined area. Then a 1-1/2-in CT string was deployed into the flowline to retrieve a sample of the blockage for diagnostic purposes. The analysis of the sample dictated the optimal cleanout strategy which was to combine a specialized rotary nozzle with pumping diesel and solvents to successfully clean out the flowline. The blockage was breached at a depth of 3,700 ft after cleaning almost 1,000 ft in less than 24 hours. The flowline was reinstated and gas production restored to >2,000 bbl/d and 8 MMcf, thus preventing the client from losing the lease.

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