Over the next 10 years, the oil and gas industry will spend US$23.4Bn on decommissioning offshore platforms and structures in the UK North Sea, generating substantial work for specialised heavy-lift, crane and construction vessels and OSVs
One of those projects set to gain from the upcoming investment in North Sea decommissioning is the Ninian Northern Platform located about 100 miles northeast of Shetland Island, in 141 m of water. Swiss-based marine contractor Allseas has deployed a purpose-built offshore construction vessel Oceanic for the second phase for the removal of the topsides and jacket of the Ninian Northern Platform. Dynamic positioning class 2 capable, Oceanic is 129 m long, 25 m wide, with two moon pools, 4,000-m water depth rated remotely operated vehicle (ROV) systems and two active heave-compensated offshore cranes. Fitted with a walk-to-work solution, Oceanic is providing construction support and accommodation for personnel working on the platform, which has not been in production since May 2017.
Under the contract with Canadian Natural Resources International (CNRI), Allseas will engineer, prepare, remove, load and dispose of the platform’s topsides, and partially remove its eight-legged steel jacket.
Ninan Northern Platform’s topsides, weighing about 12,500 tonnes, will be removed between 2020 and 2021. The jacket and substructure will be removed down to between 77.5 m and 88.5 m below water no later than 2023.
Allseas will utilise Pioneering Spirit, the world’s largest heavy-lift and pipelay, to remove the topsides in a single lift for recycling. The heavy-lift vessel used the same single-lift, motion-compensated technology in June for the removal of the 25,000-tonne Brent Bravo topsides under a contract with Shell UK. Pioneering Spirit was able to complete the operation in approximately four hours, from positioning the vessel around the platform to the moment of the lift.
The vessel had just come off a removal project in the Norwegian sector of the North Sea where decommissioning and removal projects are expected to top US$8.6Bn over the next 10 years. Working for Aker BP under a contract signed in 2017, Allseas is providing transport, installation and removal services for the Valhall oil field. Located 280 km off the Norwegian coast, the Valhall complex comprises six steel, bridge-connected platforms that stand in 70 m of water. The QP topsides is the first of the original structures to be removed from the field centre.
For the Ninian Northern Platform, Pioneering Spirit will transfer the topsides to the barge Iron Lady for load-in and transfer to the dismantling yard. Before the lift, Allseas must design the installation of underdeck lift points and remove and separate pipework and obstacles, cut the platform legs, and design and fabricate ‘horseshoe’ lifting units, support stools and grillage.
Under a contract signed with Total E&P UK in 2016, Maersk Supply Service is executing decommissioning work for the Janice & James fields and the Leadon field in the UK North Sea. In a social media post in July, Maersk Supply Service reported it had completed the removal of three towheads as part of the Janice, James and Leadon field decommissioning project.
Maersk Supply Service, a partner in the Maersk Decom JV, used its DP3 class subsea support vessel Maersk Installer to transport the three towheads to Aberdeen Harbour in July. Each weighing about 50 tonnes, the towheads were offloaded for safe disposal.
Aberdeen Harbour operations manager John McGuigan says the port was a “natural choice to support the growing decommissioning industry. In the last year, more than 10,000 tonnes of decommissioned has cargo entered the port.”
About 40 decom programmes have been approved by the UK’s Department for Business, Energy and Industrial Strategy (BEIS), which oversees all the decommissioning of offshore oil and gas installations and pipelines in the UK.