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Shell's Brent Delta single lift - in detail

Written by  Tuesday, 25 April 2017 16:21

The world’s heaviest offshore lift is primed to take place in the North Sea, on what was one of the largest UK fields, using the world’s largest vessel. 

UPDATE: the lift happened on Friday, 27 April. Watch a video of the lift here.

Watch the Brent Delta topsides arrive at Able Seaton Port on Tuesday, 2 May here.

Having already broken the offshore heavy lifting record with the 13,400-tonne Yme lift, off Norway (pictured, right, image from Allseas), last year, the close to a million-tonne displacement Pioneering Spirit mega-vessel is set to remove the 24,200-tonne topsides from Shell’s Brent field, 186km north east of Shetland.

Brent Delta is one of four platforms on the huge and iconic Brent field. Discovered in 1971, it has produced about 4 billion boe since 1976, peaking at a rate of 504,000 b/d in 1982. Initially produced mostly oil, but then also gas after conversion work in the 1990s, which saw it reach 700,000 boe/d output by 2001. 

Now, 15 years over its planned 25 year life span, Brent's facilities are being wound down. While the facilities were constructed offshore in modules, they will now be lifted out in one piece, thanks to the Pioneering Spirit, starting with Brent Delta, which has been de-manned since 2015. 

The lift will be performed in coming days using the US$3 billion (Euro €2.6 billion) Pioneering Spirit, which is the world's largest vessel ever constructed, in terms of its gross tonnage (403,342gt), breadth (123.75m / 406ft.), and displacement (900,000-tonne). It is equal in length to six Boing 747s, has deck space equal to six football pitches, and is designed to lift up to 48,000-tonne topsides and 25,000-tonne jackets. 

The removal of the facilities will be undertaken in an operation that harks back to the pioneering days of the offshore industry, when the four, huge Brent platforms were first installed, three on massive concrete bases and one on a 31,500-tonne steel jacket. Unlike then, Allseas both has a vessel to lift the facilities but can now also make use of sophisticated simulators to “trial run” the lift, in Delft, Netherlands. The alternative - taking them apart offshore - would also be “a nightmare,” according to Brent decommissioning project manager Alistair Hope. 

Brent Delta, comprising three main levels (module support frame, module deck and drilling deck) sits on a three-legged concrete gravity based hull, in 142m water depth, and is 74m x 47m, 44m high to the helideck and 132m-high to the flare tip. Some strengthening work had to be done to the platform before the lift could be done, with 300-tonne of steel installed for the lifting points, wall stiffening, and shear restraints inside the tops of the three concrete legs. Protrusions on the legs were removed to accommodate the Pioneering Spirit, leaving 5m tolerance each side.

To remove the topsides, the Pioneering Spirit’s eight sets of lifting beams – each with four, doubling acting Enerpac hydraulic cylinders, plus compressed air cylinders and compressor skids - will work with its dynamic positioning system and vast 700,000-tonne capacity (equal to 280 Olympic swimming pools) ballasting system to lift off the topsides over multiple hours. This uses four pump rooms, connected to 87 ballast tanks, including four quick drop tanks, and pumps at 37,000cu m/hr. 

First, each beam will be moved into position and connect, via yokes (two weighing 80-tonne and one 135-tonne), with the topside, maintaining position using the active heave compensation system. The beams can skid along the length of the vessel, as well as lift up and down at their lifting points, to maintain a fixed position, while the vessel continues to move. 

Image from Allseas.

The Kongsberg positioning system – driving 12, 4.7m-diameter, 80-tonne a piece thrusters - is guided by GPS, keeping the vessel within about 1.5m of its position, and then the topsides lifting system, using an optical gyroscope to see where the platform is, compensates for the rest of the motion within centrimetres – with each beam able to move independently while working together. All of this is run via remote control, and using huge computational power, to combine all the relevant positioning data – including live and predicted metocean data - and process it live in order to maintain the system’s accuracy. 

Once all beams are in place, the vessel will start lifting up, using its ballasting system, to 80% of the weight of the topside, then the last 20% will be lifted off using a compressed air system, achieving a “quick lift,” to clear the topside from the jacket, with the quick drop ballast tanks also available to continue the motion. All of this operation is powered by nine, 11.2MW engines across four engine rooms, for redundancy.

Testing such a vessel is no straight forward job. While simulation work goes so far, validation is also needed. In June 2016, Allseas performed a test lift using the module support frame from the North West Hutton platform, which was lengthened and water ballast tanks added to give additional weight. This was installed 100km offshore on a jacket, where it could be lifted on and off in different weather. 

In August 2016, Pioneering Spirit lifted out the Yme facility, which was a relatively slow lift, as it just used the hydraulic system on board Pioneering Spirit, due to the compressed air system not being ready at that time. 

Following the Yme lift, in August 2016, further trials were carried out, in harsher weather conditions. The vessel operated in 7.9m maximum wave height and 4.9m significant wave height. “It was really a task for the motion compensation system,” says Heerema. The vessel is designed to work in up to 2.5-3.5m significant wave height, depending on the length of the waves. This amounts to about two thirds of the time in the northern North Sea during summer months, says Heerema. 

Once it performed the Brent Delta lifting operation, Pioneering Spirit will put leg caps and lights on top of the Brent Delta’s concrete legs, to leave them in “lighthouse mode.” The Brent Delta topsides will then be taken to 5km off Hartlepool, northeast England, where they will be transferred to the Iron Lady barge and then taken to Able Seaton Port and skidded on to Quay 6, to be dismantled over the coming 12 months. Shell says it had assessed 131 different sites for dismantling the Brents. 

The lift is not set to be the vessel’s greatest achievement either. The Pioneering Spirit, which consumes around 200-tonne of fuel a day while steaming and 70-tonne a day while positioning, is also contracted to lift the other three Brent topsides, including the 31,000-tonne Brent Charlie platform, as well as installing the huge Johan Sverdrup topsides (weighing 19.000-26,000-tonne) for Statoil, offshore Norway. Immediately following the Brent Delta project, however, it will be heading to the Black Sea to lay the TurkStream 2 pipeline. Then in 2018-19, it will joint Solitaire, laying the twin-pipeline Nord Stream 2 over 1200km through the Baltic Sea.

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