Allseas’ dynamically positioned single-lift installation and decommissioning and pipelay vessel Pioneering Spirit has set a world lifting record, with the removal of Shell’s 24,200-ton Brent Delta platform topside today.
Located in the Brent field, about 186km off the north-east coast of Shetland, the Brent Delta topside sat on a three-legged gravity-based structure which stands in 140m water depth. Watch a video of the lift here and below.
Image: Pioneering Spirit loaded with the Brent Delta topsides.
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, at a rate of 504,000 b/d at its peak in 1982. Now, 15 years past its planned 25 year life span, the Brent field facilities are being wound down.
The removal of Brent Delta topside was done in an operation that harks back to the pioneering days of the offshore industry, when the four, huge Brent platforms were first installed. However, whereas the topsides were installed in multiple modules back then, it was removed in one piece - setting a global offshore heavy lift record.
The topside has since been sea-fastened on board Pioneering Spirit for transport to the Able UK decommissioning yard in Teesside, northeast England.
How is it done?
Pioneering Spirit 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 can lift up to 48,000-tonne topsides and 25,000-tonne jackets. She is fitted out with eight sets of two lifting beams, which can handle up to 48,000-tonne loads.
To remove the topsides, the Pioneering Spirit’s lifting beams work with its dynamic positioning system and vast 700,000-tonne capacity ballasting system to lift off the topsides over multiple hours. Some four pump rooms, connected to 87 ballast tanks, including four quick drop tanks, are involved with pump rates at 37,000cu m/hr.
First, each beam was moved into position and connected, via huge yokes with the topside, while maintaining position using the active heave compensation system.
The vessel's dynamic 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 was 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 were in place, the vessel started lifting up, using its ballasting system, to 80% of the weight of the topside, then the last 20% was be lifted off using a compressed air system, achieving a “quick lift,” to clear the topside from the concrete legs, with the quick drop ballast tanks also available to continue the motion. All of this operation was powered by nine, 11.2MW engines across four engine rooms, for redundancy.
The Brent Delta topsides will now 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.
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.
Following the Brent Delta project, Pioneering Spirit demobilize and convert to pipelay mode, then head to the Black Sea to lay the TurkStream 2 pipeline. In 2018-19, it will joint Solitaire, laying the twin-pipeline Nord Stream 2 over 1200km through the Baltic Sea.