Offshore decommissioning of oil platforms in the North Sea continues to evolve towards more efficient models. In this context, Mammoet and Allseas have integrated the loading operations of the Heather Alpha and Eider Alpha superstructures, achieving reduced operating times and costs in a single campaign.
Logistical integration to accelerate dismantling
Removing offshore superstructures involves moving structures weighing over 10,000 tons, requiring technical planning and specialized equipment. In this project, both companies opted for an integrated cargo operations strategy, allowing them to simultaneously prepare the Iron Lady barge to receive the two platforms.
Thus, this decision made it possible to optimize the use of resources and significantly reduce the time between operations, a critical variable in maritime environments where conditions change rapidly.
The role of the Pioneering Spirit in the retreat
For the extraction of the structures, Allseas used the heavy lifting vessel Pioneering Spirit. This vessel, with a catamaran-type design, is capable of lifting entire platforms in a single maneuver using lifting beams that attach to the base of the superstructure.
After their removal, the structures were moved to shallower waters where they were transferred to the barge. This step marked the beginning of a complex floating loading operation.
Precision engineering in floating operations
Unlike traditional operations, the loading was carried out with the barge afloat, which introduced additional challenges in ballast control and stability. During these maneuvers, the structures remained partially on the dock and partially on the vessel, requiring millimeter-precise timing.
Mammoet designed a system based on sliding tracks, skids, and internal beams that allowed for load distribution and height adjustments between the dock and the barge. In addition, up to 40 push and pull units were used, achieving a combined capacity of over 3,600 tons.
Reduced times and improved operations
One of the most outstanding results was the speed of execution; according to the project team, operations planned for 24 hours were completed in half the time, in a single shift.
This performance was made possible by advance planning and the integration of teams between both companies, reinforcing an operating model that is already emerging as a standard in future offshore decommissioning projects.
Final destination of the structures
Once the operations were completed, the Heather Alpha superstructure was shipped to Denmark, while Eider Alpha was moved to Norway for final dismantling.
Likewise, the experience gained in previous projects such as the Brent platforms helped to strengthen trust between the parties and to refine the technical procedures applied.
Source and photos: Mammoet