Lift analyses for decommissioning

For the Murchison decommissioning project, Iv performed engineering for the removal of parts of the platform located in the North Sea, approximately 240 kilometres northeast of the Shetland Islands. It consisted of a topside constructed from multiple modules and weighing in the region of 24,000 tonnes, and a jacket weighing approximately 14,000 tonnes, making it one of the largest platforms of its time. Iv was commissioned by Heerema Marine Contractors to carry out this work. Removal took place in successive phases during 2016 and 2017, starting with the topside and followed by the jacket.

Work was focused on multiple platform modules and included, among other things, rigging design, lift analyses to determine lift point loads, design of new lift points, and verification of existing ones. In addition, designs were prepared for grillage, sea fastening, lift-off and set-down guides, and support structures. Structural reinforcements were also designed for modules where elements had been removed during the operational phase. Furthermore, Iv performed analyses on the global structural integrity of the modules.

The platform had been modified multiple times during its operational lifespan. This involved the removal or alteration of structural elements. As a result, additional verifications were required, as well as targeted reinforcements to ensure structural integrity during hoisting and transportation.

For various modules, existing lift points were reassessed and, where necessary, modified or redesigned. Changes in weights or centres of gravity resulting from module modification during operations were taken into consideration. A further factor was that the project involved one of the largest platforms of its time. This had an influence on the scale of the analyses and the number of disciplines involved. Finally, the global structural integrity of the modules had to be ensured for multiple phases: hoisting, set-down, and transport.

The project scope and lead time resulted in a high number of design deliveries and interfaces. This made it an intensive process, demanding a structured approach within the team as well as close coordination with the client.

The engineering work performed contributed to the safe dismantling of an offshore installation in accordance with applicable regulations, fulfilling a responsibility to decommission existing energy infrastructure in a careful manner.

Following removal, the area became available for other uses such as shipping and fishing, and provided space for future offshore developments.