BP has selected Allseas to complete the subsea pipelay scope for its ultra-deepwater Greater Tortue Ahmeyim (GTA) natural gas project offshore Mauritania and Senegal. Allseas will undertake the works early December 2023 using the world’s largest construction vessel Pioneering Spirit.
Installation support will be provided by Allseas’ offshore construction support vessel Oceanic.
The contract covers the installation of approximately 75 kilometres outstanding on the two 16-inch export pipelines with field termination assemblies (FTAs) in water depths between 1500 and 2800 metres, and four 10-inch CRA infield lines with FTAs up to two kilometres long in 2800 metres of water.
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Highly complex
BP and Allseas’ commercial and engineering teams worked tirelessly to evaluate the technical feasibility of installing the pipelines and subsea structures, which were originally designed for installation with a J-lay solution.
‘This agreement demonstrates both our willingness and ability to take on highly complex and pipelay projects with fast-track planning and execution scopes,’ says Pieter Heerema, Chief Executive Allseas. ‘This opportunity re-establishes the partnership between our two companies and creates a platform on which to grow and strengthen future collaboration between BP and Allseas.’
2000-tonne tension holding capacity
The Pioneering Spirit is fitted out as an S-lay vessel, which boasts a record-breaking 2000-tonne tension holding capacity. To install the ten FTAs, the vessel will be fitted with a special 1000-tonne J-mode installation frame, designed in-house and built at Allseas’ Heijningen fabrication yard in the Netherlands.
So far, Allseas has installed more than 27,500 kilometres of pipeline worldwide.
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Pioneering Spirit
Pioneering Spirit is the largest offshore construction vessel in the world. Designed completely in-house, the vessel is designed for the single-lift installation and removal of offshore platforms and the installation of record-weight pipelines.
The twin-hulled vessel is 382 metres long and 124 metres wide. At the bow is a slot, 122 metres long and 59 metres wide, that enables Pioneering Spirit to move around a platform and lift and transport entire topsides using eight sets of horizontal lifting beams.
For jacket removal and installation, two 170-metre-long lifting beams, which can rotate on hinges, is located at the vessel’s stern. This Jacket lift system was deployed on the Ninian Northern jacket removal in 2022. Complementing the lifting systems is a 5000-tonne special purpose crane for additional lifts such as lighter topsides and jackets, modules and bridges.
In 2022, Pioneering Spirit surpassed the 330,000-tonne mark for lifted platform weight.
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