Global decom boom brings disruption to heavy lifting
The anticipated boom in North Sea decommissioning will pose unprecedented logistical challenges, not least the task of heavy lifting of topside rigs weighing more than 10,000 tons – which represent about 9% of all North Sea installations.
To date, only two vessels have coped with lifts of more than 10,000 tons: the Thialf, the world’s largest crane vessel, and the Saipem 7000. All that will change later this year when Allseas introduces the 382m-long Pioneering Spirit, which can lift 48,000 tons in one go.
Pioneering Spirit was scheduled to remove the 13,000t topside from Talisman’s Yme platform in the Norwegian North Sea last year before moving on to the 24,000t topside from Shell’s Brent Delta platform in British waters. Both projects were put on hold due to delays in delivery of some of the vessel’s components.
The introduction of such a large vessel will greatly simplify dismantling of topsides, with all but the most essential decontamination and disaggregation work to be conducted onshore in a decommissioning yard.
“The Pioneering Spirit is a game changer that will bring significant benefits to the whole sector, including recycling,” Neil Etherington of Humberside-based Able UK, which will recycle 98% of the Brent Delta platform, told DecomWorld.
“To prepare for the topside we’re building 120m of new quay, around half of which will have a 60 t/m² load capacity. It’s ideally suited to receiving the barge that will be dispatched from the Pioneering Spirit containing the load.”
To lift the Brent Delta platform, the Pioneering Spirit will attach hydraulic clamps under the structure before pumping water out of its ballast tank to lift it in seconds. Operating such a huge ship does not come cheap and the boat will have to be kept busy to justify its $1.7 billion price tag. Allseas has a contract from Shell to remove the topsides of two of the other three platforms in the Brent field - Bravo and Alpha – and an option for the fourth platform, Charlie.
Pioneering Spirit will lift the Brent Delta platform in seconds (Image credit: Shell)
And there is likely to be more work for the Pioneering Spirit, especially in the central and northern parts of the North Sea, where platforms tend to be larger to cope with deeper waters and harsher weather. According to trade association Decom North Sea, the UK and Norway sectors of the North Sea possess a combined 4.5 million tons of steel – associated with fixed steel or concrete-gravity base topsides – which will all eventually need to be decommissioned. The largest topside for a fixed installation is Norway’s 53,000t Gullfaks.
Before the advent of the Pioneering Spirit, large platforms were commonly removed using processes known as “piece small” to cut the topside into pieces, or “reverse install”, which involved cutting and removing large modules in reverse order to installation. The latter method was used to decommission the North West Hutton platform, 86 miles off the Shetland Islands, in 2008. It took 22 modular lifts to complete and the largest module weighed 2,800 tons.
Building to local requirements
Despite its imposing build, vessels of the size of the Pioneering Spirit are not about to play a role in heavy lifting in the Gulf of Mexico, according to Tom Cheatum, business manager of Versabar.
“It’s old technology given a new purpose because of its massive size,” Cheatum told DecomWorld. “It’s well designed for the North Sea environment. But it would be enormously expensive to transport it to the Gulf of Mexico and we don’t really need a vessel that big here. Platforms tend to be smaller as the weather is more benign.”
Nevertheless, there is a huge amount of decommissioning to be done in the GoM, where oil companies face the same problem of ageing assets. Mark Kaiser, director of Louisiana State University’s Research and Development Center for Energy Studies at Louisiana State University, says up to 250 structures will be removed in the region this year and the numbers will rise in future as low oil prices provide incentives against deferring the process.
As in the North Sea, the frequency of decommissioning places huge demands on offshore equipment resources. Figures from the US Bureau of Safety and Environmental Enforcement show that as of February 2015 there were 241 platforms in the Gulf in the category of “idle iron”, and a further 294 on expired, or terminated, leases.
Versabar’s VB10,000, the largest heavy-lift ship operating in the GoM, is capable of lifting 7,500t objects. It had a noticeable success with the lift of the Red Hawk Spar in 2014, but could not raise larger rig structures, causing Eric Smith, associate director of the Tulane Energy Institute, to question the ability of existing ships in the GoM to lift giant structures such as Shell’s Ram Powell TLP. But Versabar is able to use its Versatruss system for 15,000-20,000t platforms, according to Cheatum.
“Versatruss distributes the load evenly on the centreline of two barges and is scalable up to about 20,000 tonnes. We’re doing proposals for large lifts at the moment,” he said.
Meanwhile, Allseas has started building an even larger vessel than the Pioneering Spirit. Its topside lift capacity will be 72,000t and it will have a width of 160m, whereas Pioneering Spirit is 124m wide. Allseas expects it to be operational in 2020. Together, the two Allseas ships could handle between 12-18 topsides a year, radically altering the decommissioning market in the North Sea.
David W. Smith