Aegir’s first project

Heerema Marine Contractor’s new multi-purpose construction vessel Aegir completed its first job in the Gulf of Mexico. Meg Chesshyre reports.

Aegir. Images from Heerema Marine Contractors.

The first mobilization for Heerema Marine Contractor’s newbuild multi-purpose deepwater construction vessel Aegir was for the subsea part of Anadarko’s Lucius Spar project in the Gulf of Mexico, which was completed early in 2014.

The job was awarded before the vessel was even built, as Meredith Taylor, senior project engineer with Heerema Marine Contractors (HMC), based in Houston, explained at the International Marine Contractors Association’s recent annual seminar in London.

The decision to build a new vessel was taken because Heerema, as a key player in complex deepwater construction for over 10 years, wanted to maintain and expand its position in the expected growth of the market in complex high-tech field developments.

A mix of high-end capabilities were chosen for the new vessel, including heavy pipelay to 2000-tonne top tension and 3500-mwd, heavy lifting to 4000-tonne capacity using a mast crane, heavy reeling to 800-tonne top tension, plus lifted reels and the use of a pipelay abandon or recover system for deepwater lowering. The pipelay tower is called an R J tower by HMC, because it can perform reel-lay and J-lay, by using different ways to hold the pipe – friction clamps and hang off collars.

The lifted reels concept meant that the vessel could stay on the field with the reels being brought from shore. The width of the vessel (46.2m) meant that it was possible to put three reels across at a time.

HMC also wanted to make the new vessel, named after a Norse god of the sea who ruled the waves, back to back compatible with its existing deepwater construction vessel the Balder. A monohull was selected for good transit speed (12 knots) for worldwide operations and good workability in the long swells found offshore West Africa and Brazil. It was based on an existing vessel design, a customized Ulstein Sea of Solutions SOC 5000, to speed up the payback time.

“We decided to build the Aegir in 2010,” Taylor says. “We were negotiating the (Anadarko Lucius) contract in 2011. At the start of 2012 the contract was awarded just after we had laid the keel, so we were having to do analysis and design procedures based on equipment that hadn’t yet been fabricated or installed. We had to set up the offshore spooling yard before the vessel had arrived in Rotterdam (for installation of the pipelay equipment by Huisman).”

Once the pipelay equipment was on board, the vessel sailed to the Gulf of Mexico for some trials then started straight away on the Lucius project. It emerged during the trials that the weight of the reel and the exact height of the crane resulted in a pendulum effect. The natural frequency of the pendulum exactly matched the vessel’s response to the long swell. The solution was a dampened tugger system. This gave a change in damping according to the velocity of the pendulum. Interestingly, “not only did it damp the motion of the reel, but it also damped out the whole system, so the vessel stopped rolling as well.”

The Lucius project comprised the subsea tieback of six wells in a water depth of 7100ft. The Aegir’s scope of work consisted of four 8in., three 6in. flowlines, six 8in. SCRs (steel catenary risers), a 140-tonne manifold and a crossing mattress. Heerema’s DCV Balder installed the suction piles, the SPAR mooring and another manifold, and the DCV Thialf installed the topsides.

The pipelay required the use of four reels. The heaviest one weighed 2754-tonne in total, including the reel and rigging. The pipe weight was 1646-tonne. The weather was good, with a significant wave height of only 1.4m for the first reel for a short period, the other sea states being lower. This meant it wasn’t possible to test the system to its limits.

Computational fluid dynamics analysis was used to model hydrodynamic loads. A radar wave measurement system in the moonpool allowed for the monitoring of the waves compared with those outside. Steering winches added as a result of the analysis gave extra control and damped out some of the pipeline end termination movements during the lowering.

The moonpool was also used to lower the 140-tonne manifold down to 6820ft using the deepwater lowering system, having been handed over from the crane using a 45m synthetic sling. The system was designed to operate in up to 3m sea states, but once again the weather was perfect. “It was like a millpond when we installed it,” Taylor says.

In mid-October 2014, the Aegir started on a contract transporting and installing infield flowlines, subsea structures and moorings for the INPEX’s Ichthys LNG project, on a sub-contract from McDermott Australia. HMC also has a contract for the Aegir for the installation of the Shell Malikai tension leg platform in Malaysia.