On 22 August, Swiss-based offshore contractor Allseas entered the North Sea
decommissioning market in record-breaking style. Its dynamically positioned
single-lift installation/decommissioning and pipelay vessel “Pioneering Spirit”
successfully removed the 13,500 t Yme platform in a single lift, setting a
record with its first commercial contract.
Located in the Yme field in the Norwegian sector of the North Sea, approximately 100 km west of Stavanger, the Repsol-operated Yme mobile offshore production unit (MOPU) is a jack-up type platform standing on three, 3.5 m diameter steel legs, inserted approximately 10 m inside the subsea storage tank columns at 93 m water depth. The decision to remove the platform was made in 2013, and the contract for the removal of the topsides was subsequently awarded to Allseas; what would ultimately become the first job for the 382 m long and 124 m wide heavy lift vessel “Pioneering Spirit”.
Following the successfully completion of offshore trials, “Pioneering Spirit” arrived in the Yme field on 17 August 2016. After receiving the necessary approvals from Repsol, the vessel moved backwards towards the platform for installation of the cutting tools in the platform legs, a process which took approximately 24 hours. With the tools in place, “Pioneering Spirit” turned, moved into the 500 m zone and positioned herself around the platform. Five yokes, purpose-built to support the platform during the lift and mounted on the vessel’s topsides lifting system, were moved into position and carefully connected to pre-determined strong points on the underdeck.
Cutting of the three platform legs – from within, using an oxy-fuel-flame technique – commenced in the morning of 22 August, and took several hours to complete. Once the operation was finalised, the platform was lifted from the platform legs in a “fast lift” – powerful hydraulic levers at the tip of each of the vessel’s lifting beams work in unison to raise the load 2 m clear of its severed support legs.
Although the lift was originally expected to take a matter of seconds, in reality it took approximately a minute to raise the platform deck to the necessary 2 m clearance. This was due to the air pressure system that speeds up the upwards movement not being fully commissioned at the time of the Yme lift. Once the system is fully tested it will enable “Pioneering Spirit” to lift topsides in a matter of seconds. This will enable Allseas to perform lifts in much inferior weather conditions – the significant wave height was about 2 m during the lift, and at times a bit more.
Immediately after the fastlift “Pioneering Spirit” moved out of the 500 m zone, and the platform was sea-fastened on board. A day later, reaching a top speed of 14.2 knots, “Pioneering Spirit” arrived at Norway’s new Lutelandet dismantling yard, north of Bergen, for inshore transfer of its cargo. The platform was subsequently transferred to Allseas’ purpose-built cargo barge “Iron Lady”, and loaded in to the quayside for dismantling.
What’s next for Pioneering Spirit?
“Pioneering Spirit” returned to Rotterdam early September, and preparations are now in full swing for her next job, removal of Shell’s 23,500 t Brent Delta topsides in the summer of 2017. For this job, she will be fitted with the final four of her 16 topsides lifting beams, and the lifting yokes used for the Yme lift will be replaced with new, purpose-built yokes suitable for the Brent Delta platform.
The vessel will be ready to perform the Brent Delta lift in May, but the actual timing of the job will ultimately come down to Shell. After Brent, “Pioneering Spirit” will install three platform topsides on Statoil’s Johan Sverdrup project in Norwegian waters, in 2018 and 2019, after which she will return to the Brent field to remove the Bravo and Alpha topsides, along with the Alpha steel jacket, in 2019 and 2020.