Specially designed powered reel used to recover mooring lines cost-effectively.
Acteon company Aquatic played a key role in 2008 in the decommissioning and removal of a redundant loading buoy in Venture Production’s Kittiwake field in the central North Sea. Aquatic was responsible for recovering the eight mooring lines that had secured the structure in 85 m of water, plus its two, 8-in flexible risers and an umbilical used to convey power to valves on the buoy’s pipeline end manifold.
Rather than using an anchor handler, Aquatic chose to fit one of its modular powered reel systems to the back deck of a less-costly DP2 class vessel, the Volantis. Once cut at the seabed using an ROV, the mooring lines (individually comprising 765 m of wire rope terminated at the top and bottom by 265 m and 82.5 m, respectively, of 3¼-in chain) were each recovered directly to a reel specially designed to withstand the unusually high compression forces generated by the spooled chain. Rather than the 10 tonnes spooling-on load rating of the company’s standard AQSR50 reel, the one used here had a reinforced hub rated at 30 tonnes; its tower drive system was also upgraded to provide a maximum torque rating of 150 Te/m.
Aquatic completed the project in just two trips from the shore. Four mooring lines plus the risers and the umbilical were recovered to the single reel on the first trip; and the remaining four lines recovered on the second.
This was the first project of this kind carried out by Aquatic. It came in on budget and the offshore operations were without incident. The company is reviewing the design of the powered reel system used here in order to increase its recovery capacity and is looking forward to applying the lessons learned on this occasion to similar projects in the future.