Final preparations are being made for what will be the heaviest ever offshore lift and the first of the once prolific Brent field platforms removals using Allseas’ mega-vessel, the Pioneering Spirit. Elaine Maslin reports.
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Allseas’ Pioneering Spirit during pipelay mode with the stinger and stinger transition frame (STF) installed in the bow slot. In transit mode, the combination of both the stinger and STF increase the vessel’s overall length to almost 450m. Photo from Allseas. |
Last year, Allseas’ mega-vessel Pioneering Spirit vessel performed its first project, taking out the 13,500-tonne Yme platform topsides in a single lift offshore Norway. Early this month [May], it will sail to the Brent Delta facility, 186km off Aberdeen, to remove Shell’s 24,500-tonne Brent Delta topsides, before then heading to the Black Sea to lay the TurkStream pipeline. As OE went to press, the firm also won a contract to lay the twin-pipeline Nord Stream 2 over 1200km through the Baltic Sea, in 2018-19, using the Pioneering Spirit, as well as Allseas’ Solitaire and Audacia pipelay vessels.
In April, the vessel’s final four lifting beams, installed after the Yme lift, were tested, with a 15,600-tonne cargo barge load, ready for the job, with final commissioning due to be completed ahead of a test lift in the Dutch North Sea, using a dummy platform. The vessel’s pipelay stinger was also trial fitted in April, ready for its TurkStream job. Work will also start this year on the vessel’s jacket lifting system, to be installed aft, as well as installing a new Huisman, 5000-tonne, tub-mounted crane.
For Allseas, the Brent Delta project will further validate some 30 years’ work, proving and building its heavy lift vessel concept, which at 48,000-tonne topsides and 25,000-tonne jacket lifting capability, outstrips that of any other vessel in the market. The 382m-long, 124m-wide vessel, with a 122m-long, 59m-wide bow slot (and 1 million-tonne displacement at full draft), was built in South Korea by Daewoo Shipbuilding & Marine Engineering (2011-2014) at a cost of US$3 billion.
Fred Regtop, Captain of Pioneering Spirit, says that in August last year, the vessel, which can sail at 14 knots and has 95 MW installed power, outperformed simulations for the Yme lift. Allseas’ founder Edward Heerema says that in November 2016, the vessel then performed well when tasked with performing another test lift on a dummy platform installed in the Dutch North Sea, with 4.9m significant wave height and 7.9m maximum wave height.
For Shell, the Brent Delta topsides removal comes after 10 years’ preparation work on the Brent field facilities, which has a further three platforms, also all due to have their topsides removed by Allseas in coming years.
Shell just completed a public consultation on its Brent Delta decommissioning plans, which resulted in some calls from environmentalists for more information. However, there have also been a lot of learnings through the project. For example, Shell thinks it can reduce the preparation scope required for the lift by 25% on the next project (Brent Bravo), including having less reinforcement work on the platform, but also by using concrete instead of installing new steel for the lifting points.
Brent Bravo provides different challenges, however, with an underwater obstruction on the legs meaning extra ballasting for the vessel to be able to clear the site before sailing away. Charlie, the final facility that will be removed, will be the heaviest, at more than 30,000-tonne. While at the start, Allseas thought once one lift was done, the rest would be similar, the difference in platform design means this isn’t quite the case, said Heerema at a briefing on the vessel in April.
However, Brent Delta was still the focus. Visiting the Pioneering Spirit, OE was told some 500 people were working and living aboard in order to get it ready for the job, as well as completing commissioning of the pipelay system, ready for its Turkstream pipeline project in the Black Sea immediately after the Brent Delta removal. Moored alongside was also Allseas’ new acquisition, the newbuild support vessel Volstad Oceanic.
Brent Delta and two of the other three Brent topsides to be removed (Bravo and Alpha) are due to be taken to Able Seaton Port, Hartlepool, which underwent £28 million investment to be able to do the topsides dismantling work. Off Hartlepool, the topsides will be transferred onto stools on the Iron Lady barge, and towed onshore before being skidded on to Quay 6. Once there, the platform will effectively “disappear” within 12 months, says Neil Etherington, business development director at Able, with about 97% of it to be recycled.
While the Yme lift was performed just using Pioneering Spirit’s hydraulic system, due to the compressed air system being not quite ready, the Brent Delta removal will use the full system. Using compressed air allows for a faster lift off, having had 80% of the load already taken up through ballasting, Heerema says. The operation is done using the vessel’s complex topsides lifting system, which involves coordinating eight sets of two lifting beams, each able to move independently both up and down but also aft, forward, to port and to bow, all in coordination with the vessel’s DP system, to ensure the lifting arms can safety touch onto the platform being lifted without being impacted by vessel motion. Each pair will move into place in succession before the final lift.
Allseas has also been learning. After taking delivery of the vessel in Rotterdam, the firm added a sort of slot brace. This connects the two bows together during transit to stop any deflection caused by water pushing on their insides from potentially putting strain on the topsides being carried.
Following TurkStream, between 2018 and 2019 the vessel will install three platform topsides for Statoil’s Johan Sverdrup Development project in Norwegian waters. We’ll bring you more in next month’s OE.
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