The successful lifting of the topsides of the decommissioned Yme platform offshore Norway by the world’s first single-lift vessel in August was a watershed moment for the offshore history books.

With the North Sea set to be a ripe hunting ground for decommissioning projects large and small over the course of the next several decades, the proof that innovative and bold Swiss-based contractor Allseas’ unique flagship vessel is up and running was a rare and welcome bright spot in what has been a downbeat time for the marine construction and heavy lift sector.

Yme was the first commercial job for the twin-hulled Pioneering Spirit, with the Repsol-operated jackup production facility’s 13,500-tonne topsides well within the lift vessel’s capabilities, but it still represented the largest single lift ever undertaken offshore.

Bigger tasks

Bigger tasks await the offshore behemoth. Next year in the U.K. North Sea it is set to tackle what will be a world-record single lift of Shell’s Brent Delta platform topsides, weighing 23,000 tonnes.

The oil company’s three other Brent platforms, Alpha, Bravo and Charlie, also are lined up for similar topsides removal work over the next few years under a contract and options awarded to Allseas in 2013. Those four Brent field topsides decks have a combined weight of more than 100,000 tonnes, with the heaviest weighing in at about 30,000 tonnes.

The contract also includes the removal of Alpha’s steel jacket (the other three Brent platforms are concrete gravity-based structures). All sit in water depths of about 140 m (459 ft) about 186 km (115.5 miles) offshore.

Trial run

A few weeks before the work on Yme was carried out, there was a crucial first offshore test for the topsides lift system beams on the Pioneering Spirit. It successfully installed a test platform topsides weighing 5,500 tonnes on a substructure in the K-13 Field in the Dutch sector of the North Sea Aug. 7.

The motion-compensated lift system accurately positioned the topsides, after which installation went exactly as planned, according to Allseas at the time. It also then carried out dynamic-positioning (DP) trials as well as a series of installation and removal trials with the test platform topsides under varying conditions.

The Class 3 fully redundant DP and maneuvering system was supplied by Kongsberg Maritime and relies on a distributed and open system design, employing a fully backed-up systemwide standardized communication network. This was a complete solution custom-made for the vessel’s uniquely demanding duties.

The Pioneering Spirit has two fully equipped and redundant Kongsberg Navigation bridges, one fore, one aft and occupying separate fire zones. The “K-Bridge” system also utilizes radar transceiver interface technology and has the ability, for example, to combine radar images from multiple radar transceivers and display them as a single composite picture. This provides a 360-degree view around the vessel and eliminates blind spots, according to Kongsberg.

Yme lift

It was after the successful test on K-13 that the maiden job on Yme about 100 km (62 miles) offshore was undertaken. The jackup facility stands on a trio of 3.5 m-diameter (11.4-ft) steel legs, which are inserted inside the field’s subsea storage tank columns in a water depth of 93 m (305 ft).

Pre-lift preparation work by Allseas included the installation of temporary strain fenders around caisson and leg cutting and the design and development of leg-cutting equipment.

The sheer size of the Pioneering Spirit—measuring 382 m (1,253 ft) in length and 124 m (407 ft) in width— enables it to have a slot between its bows that is 122 m (400 ft) long and 59 m (194 ft) wide. This enables it to straddle platforms such as Yme and other larger facilities to remove topsides in a single lift. In this first case it used eight sets of horizontal lifting beams.

The fact that it can do this without the need for jacking down the platform also results not only in a simpler and safer operation but also further cost savings for the field operator.

Once in place, the Yme topsides were lifted and offloaded in a matter of seconds, sea-fastened onboard and then transported to an onshore decommissioning yard at Lutelandet in Norway.

The vessel then returned to Rotterdam in the Netherlands for its remaining four topsides lifting beams of 65 m (213 ft) in length to be installed ahead of its work on the Brent Field, which is due to start with the Delta topsides in the summer of 2017.

Motion compensation system

The active motion compensation system is a crucial aspect that enables the vessel to undertake large lifts in harsh environments, in waves of up to 3.5 m in height, while eliminating impact forces on the topsides.

According to Allsea’s Founder and President Edward Heerema, on Yme it worked absolutely to plan. “She was very steady on the waves, and the motion compensation system worked very accurately, so we were delighted with the performance,” he said during an interview at the Offshore Northern Seas event in Norway, just days after the Yme work was completed.

Heerema, whose father Pieter Schelte Heerema famously was the first to think big and draw up the vessel’s original design several decades ago, has made that vision a reality—albeit at a cost of more than $2 billion. He pointed out that the vessel’s next job for Shell will be another world record lift. “Nobody before has lifted 13,500 tonnes in the history of the offshore, but the Delta lift will be even more of a record because it will be 23,000 tonnes,” Heerema said.

Doubters

While there were plenty of doubters out there who felt that the concept would never work, Heerema praised those—especially oil companies—who he said recognized the technical possibilities and potential. “They asked dozens of questions, critical questions, but we were able to convince them that it would work and they went with us, and that is also very remarkable,” he said.

His faith in the giant single lift concept is now increasingly set to pay off. Aside from the Yme and Brent Field decommissioning work, Statoil also stepped forward, awarding Allseas a contract not for removal but for transportation and installation of topsides for three of the platforms for its Johan Sverdrup field offshore Norway, which is currently under development. It also has an option to install the interconnecting bridges between the drilling, processing and living quarter installations.

The topsides weights will range from about 19,500 tonnes up to 26,000 tonnes, with the installation work expected to get underway for the drilling platform’s topside in 2018, followed by the processing and living quarter topsides in 2019. The field is due onstream in 2020.

Big is beautiful

The Pioneering Spirit was built at Daewoo Shipbuilding and Marine Engineering’s yard in Okpo, South Korea, after being ordered in 2010. With a topsides lift capacity of 48,000 tonnes and a jacket lift capacity of 25,000 tonnes, it is undoubtedly big.

But apparently not big enough. Allseas made it known in 2013, while the first vessel was being built, that it had a larger one on the drawing board.

Named Amazing Grace, Heerema said its concept emerged after Allseas carried out lifting studies for a number of clients that showed that for some older, very large platforms, even the Pioneering Spirit was not big enough. The second vessel, if it does come to reality, will be able to lift wider, longer and heavier topsides than its predecessor. It could lift up to 77,000 tonnes, the company has said previously, with a vessel width put at 160 m (525 ft).

SIDEBAR:

$12 billion saving on decommissioning using SLVs

Single-lift vessels (SLVs) could help the offshore industry save almost $12 billion on the decommissioning of North Sea projects between 2016 and 2040, according to analyst Douglas-Westwood.

The analyst said in its latest North Sea Decommissioning Market Forecast covering the period 2016-2040 that it expects the U.K. and Norway to dominate abandonment expenditure due to the large amounts of installed infrastructure in both sectors, much of which is past design life.

Decommissioning costs are forecast to total $88 billion over the period, but Douglas-Westwood’s report states those costs could be as low as $76 billion if SLV technology “is fully embraced and successful.”

Legacy costs

The report added, “We expect spend on decommissioning in the North Sea to grow extensively in the next few years, becoming a major part of oil and gas industry expenditure. This will be spurred on by the low oil prices, which have led operators to embark on major cost-cutting exercises. As a result, removing legacy maintenance costs from their annual budgets will be crucial.

“Operators have known for many years that decommissioning had to happen, but deferral has generally been chosen, with operators preferring to pay the smaller maintenance costs than the large (one-off) decommissioning cost— even for fields that have ceased production.”

It added that due to the large number of aging fixed platforms in its sector, the U.K. is expected to see the majority of the early abandonment activity, with large-scale Norwegian activity following later in the forecast period.

Contact the author, Mark Thomas, at mthomas@hartenergy.com for more information.

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