Boskalis Annual Report 2020

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HUNDREDS OF ASPECTS The Viking Vulcan/Bravo project involved the removal of 18 platform topsides, including wellhead, processing and accommodation modules, as well as 21 steel foundation jackets, three bridge structures and two undersea templates. The largest of the structures lifted by the Bokalift 1 weighed in excess of 1,500 tons. “A project of this size requires a lot of engineering, calculations and CAD drawing,” explains Leenhouts. “It takes a lot of ingenuity and teamwork to work out how to remove the topsides from the jackets safely, which cutting and lifting methods to use, which temporary structures are needed to work in hard-to-reach places without risk, the amount and type of lifting points needed for the lifting work, how the stability and integrity of both the structures to be lifted and the crane vessel can be safeguarded, and how to optimize the workability in different weather conditions and sea states. We also needed to decide where to locate the grillages (support structures) on board the Bokalift 1 to transport the platform parts safely while keeping them balanced. Overall, there were hundreds of aspects to be kept in mind to guarantee a safe and successful operation.” PLATFORM REMOVAL “We worked at many different locations in 2020. In addition to the topsides, jackets and other elements in the Viking Vulcan/Bravo oil field, we removed some parts of foundation piles left over from the 2019 platform removals,” says Leenhouts. “We used internal cutting tools (ICTs) to cut through the steel foundation piles. The ICT is a cutting device that makes a horizontal or inclined cut in the piles with a combination of ultra-high-pressure water jets and sand crystals. In that way, we were able to cut the piles three meters below the seabed from the inside.” Before the ICTs could be used, several meters of sand had to be removed from the piles after the topsides had been removed from the jackets. “We mostly used the airlift tool for that work. That’s a modular pipe structure which can be more than sixty meters long. It pumps air to the bottom of the pile to loosen the compact sand column,” explains Mabélus. “After we had cut through the jacket piles, we were able to lift the jackets from the seabed with the Bokalift 1 crane. For several topsides and jackets our internal lifting tools were used. These are hydraulic plugs

that are clamped into the tubular elements of the platform structures. The parts of the platforms that we removed were lifted onto the deck of the Bokalift 1 with the 3,000-ton crane and seafastened. They were then taken to the specialized yard of our subcontractor Veolia Peterson in Great Yarmouth for dismantling and recycling.” BOKALIFT 1 The heavy lift vessel Bokalift 1 played an important role in both decommissioning projects. “With an enormous deck of more than 7,000 m², this unique vessel can accommodate huge installations and large amounts of equipment, and the centrally located crane with a lifting capacity of 3,000 tons is incredibly strong and can reach the entire surface of the deck,” Leenhouts says. “By virtue of the well-positioned crane and the vessel’s DP2 dynamic positioning capability, we were able to perform the heaviest lifts where there was extremely little room to maneuver, even in challenging weather conditions. In addition to the performance of the Bokalift 1, the team spirit during both campaigns was excellent.” ALL HANDS ON DECK The second phase of the Viking Vulcan/Bravo campaign started in mid-April 2020 and was completed on schedule two months later, despite the many restrictions due to the COVID-19 pandemic that had broken out shortly before the start of the project. “We had a large team of more than 120 people on the Bokalift 1. It was very much a question of “all hands on deck”. In addition to our own colleagues making up the marine crew and project team, there were a lot of subcontractors on board: ROV and crane operators, specialists for the internal dredging, cutting and lifting tools, welders, cutters, fitters and riggers, as well as scaffolders and rope access technicians. Everyone was dedicated and flexible, particularly when it came to crew changes during the COVID-19 outbreak, for which Boskalis had set up a special test facility and quarantine program. This was acknowledged by the clients of both projects, who expressed their satisfaction and appreciation regarding the successful execution. All the Boskalis colleagues, subcontractors and support organizations can be very proud of the end result,” says Leenhouts.