Two world lifting records are being claimed for moving the 11,683t integrated deck module of the Shearwater offshore oil and gas platform. The first record, for the heaviest load out, was a job for 426 axle lines of Mammoet SPMT at Amec Process & Energy’s Wallsend yard on the river Tyne in the northeast where the module was built over the last two years (Mammoet claims… April 2000, p5). The second record, for the heaviest object ever lifted by mankind, is claimed for the heavy lift crane barge Thialf, owned by Dutch heavy transport and marine contractor Heerema. This lift beats a previous claim by PSC for an 11,000t lift, using strand jacks, of the RBS-8M semi-submersible deck Deepwater Nautilus at Hyundai’s yard in Korea last year (PSC and Van… Oct99, p3).
On Thursday 6 April Thialf lifted and placed the £300m ($480m) deck module in the Central Graben area of the North Sea, just over 200km east of Aberdeen in the Shearwater field. The following weekend the barge lifted and placed the 800t cabin module, the 600t incinerator module and the flare stack and bridge which links the production platform with the wellhead platform, completed last year. Weather is a critical factor as the lift could only be done with a wind speed of less than 25 knots and a sea state of less than 2m. The successful lifts meant the project remained on schedule for its production start-up date of 1 July.
Thialf is Heerema’s largest crane vessel and one of the largest in the world, according to its owner. Maximum lifting capacity using the two cranes in tandem is 14,200t. Even the auxiliary hoist of each crane has a lifting capacity of 907t. Lifting height of each crane on the main hoist is 95m above the deck and, with a load of 2,990t, lowering depth is 351m. Overall length of the vessel is more than 200m and it is 88m wide. There is accommodation for 736 people, the helicopter deck is large enough for a Chinook 234 and it sails at up to 6kmh.
Shearwater, a high pressure and high temperature field (1,000 bar, 180°C) was discovered by ARCO in 1988. To illustrate the high pressure, Shell describes it as the equivalent of three elephants standing on a postage stamp. Licence holders are Shell UK, Esso Exploration & Production UK, Arco British and Superior and Canadian Superior Oil (Mobil). The £876m ($1,402m) development is operated by Shell Expro. Gas will be transported via a new 463km pipeline to Bacton gas terminal on the east coast. Enough gas will be produced to supply a city the size of Sheffield. A 12 year life is expected for Shearwater but the facilities are designed to last for 30 years so that other smaller accumulations nearby can be exploited afterwards.
