First Wind-Powered Offshore Gas Platform Loaded Out in the Dutch North Sea

The N05-A platform is the first offshore gas platform in the Dutch North Sea to be powered entirely by wind power – harnessing electricity via cable from the nearby 113.4 MW Riffgat offshore wind farm. 

The platform is part of the GEMS (‘Gateway to the Ems’) project, which focuses on developing field N05-A and other fields in the area, situated in the waters on the border of the Netherlands and Germany. The electrification of the N05-A platform is expected to reduce carbon emissions by over 85% throughout the project’s duration.  

HSM Offshore approached Mammoet to support the load-out of the 3,050t N05-A topside and 3,150t jacket at HSM’s quayside fabrication facility in Schiedam, Rotterdam. Mammoet’s scope for the project was to successfully load out both components onto a barge for shipping to sea. ONE-Dyas, the platform’s owner, managed offshore sailing and installation. 

The assembly and weighing of the jacket and topside were done using mobile cranes, conventional trailers, and SPMTs. The first operational phase of the project was to support the movement and assembly of the jacket, which was fabricated and assembled in two parts. Mammoet supported the heavy transport and upending of the jacket’s rows with four mobile cranes carrying out the lifts: two LTM 1650 (650t) cranes and two LTM 1450 (450t) cranes. Its pile sleeves were installed using a 750t mobile crane.  

Once in the correct position, the top section of the jacket was moved to the quayside, where heavy lifting was performed by two sheerlegs. This created the space for the bottom section to be driven underneath to join the two parts. 

Self-Propelled Modular Transporters (SPMTs) were driven underneath the topside. These SPMTs drove the structure outside the fabrication facility and onto the quay. Mammoet then supported the installation of a pedestal crane onto it using conventional trailers and mobile cranes.  

With the jacket and topside complete, SPMTs picked both up, and their final weights were determined using Mammoet load cells. The load-out operation could begin after the weighing of both structures. One of the biggest challenges of the project was the load-out phase. Typically, for loadouts of this type, a barge would receive either a topside or a jacket, not both. However, for this project, both structures needed to be loaded onto the same vessel to shorten the overall schedule. This created space and engineering challenges, as the team also had to allow room to install pumps and winches onto the transport vessel. The combined loads also meant conventional mooring methods couldn’t be applied.  

“The mooring was quite critical, and we had to do a lot of engineering,” explains Sven Segeren, Project Manager at Mammoet. “Normally, we would use a configuration of winches to moor and stabilize the vessel, but that wasn’t possible because of the force of the considerable loads. The loads on the winches were too high and the bollards not strong enough, so a small spud leg barge was used to secure the vessel and keep it in position before, during, and after load-out”. 

The jacket foundation and topside load-out operation was completed in just two days. Four trains of 32-axle line SPMT trailers were used for the movements. Due to factors beyond the project’s control, the execution date was unknown for a significant period. Therefore, Mammoet was asked to prepare a temporary load-in venue so the next project at the HSM Offshore yard could continue unimpeded. The team prepared Mammoet’s yard in Schiedam, next door to HSM Offshore, to perform a load-in of the topside and jacket. An area was temporarily ready to house the components, equipment was reserved, and necessary engineering plans were made. This space was ultimately not required. However, Mammoet could react and adapt to a changing operational environment.