The Valemon Development Project of Statoil, the operator, and co-license holders Petoro, Enterprise Oil and Centrica, concerns a gas and condensate field located 160 kilometers to the west of the Norwegian city of Bergen in the North Sea. The field, which was discovered as early as 1985, contains 206 million BOE (Barrels of Oil Equivalent) and is one of the largest fields in the North Sea that has not yet been developed. In June 2011, Statoil and partners were issued the permit for its development by the Norwegian authorities. Statoil expects to be able to start producing gas and condensate in Q4 2014. In view of the water depth of 133 meters, the Valemon process platform required a 157-meter-high jacket with a footprint of 45 x 45 meters. As a result, it will weigh approximately 10,000 tons and will have to be anchored to the seabed by 60-meterlong piles. Designing such a giant has proven to be a real challenge. In particular because initially Statoil considered to reuse the topside of the existing Huldra platform for the Valemon process platform. The company later decided to have a new topside built in the Far East. “In 2010, Statoil first asked HFG Engineering to carry out a FEED study and then to make a detailed design,” says Aren Bezuijen. “After the EPC contract was awarded to the Heerema Fabrication Group on 20 October 2010, the fabrication project was able to start in April 2011 at our yard in Vlissingen. The load-out operation is planned for 9 May this year, and the sail-away for 25 May. Heerema Marine Contractors (HMC) will then use Thialf, its crane vessel, to install the jacket and the wellhead module offshore.” From draft to detailed design
Cees Spaans continues: “In 2009, we gained considerable experience with Statoil when carrying out the FEED
study for the Gudrun jacket. However, the FEED study for the Valemon jacket posed us a much greater challenge. As with Gudrun, Aker was also requested to carry out such a study. With both FEED packages as input, Statoil then invited tenders from five contractors. Eventually, our version was selected and in September 2010, we were able to start making the detailed design in collaboration with SNC. A month later, the EPC contract was awarded to the Heerema Fabrication Group. A true challenge when designing the jacket was to keep control of the weight. We had to deal with a structure weighing more than 9,000 tons. This quickly starts to approach the limits of large crane vessels including the Thialf and Saipem 7000. Because these Semi-Submersible Crane Vessels (SCVVs) have different capacities and employ different working methods, the Valemon jacket would have been too heavy if it had to be suitable to be installed in sea by either one of the vessels. Fortunately, Statoil decided at an early stage which installation contractor they wanted to employ. This was HMC, and as a result we could tailor the design completely to the specifications of the Thialf. When doing the FEED study, we still had to take account of the fact that Statoil considered to reuse the topside of Huldra for Valemon. But after starting the detailed design, it quickly became clear that they had decided to build a new topside.” The special thing here was that a wellhead module also had to be designed and fabricated. These contracts were awarded to HFG Engineering and Heerema Fabrication Group as well. “The current trend is for operators to want to have a jacket including a wellhead module available long before the topside is delivered,” says Cees Spaans. “After the installation of the wellhead module, numerous wells can be drilled before the topside is installed. We actually designed the
Project Manager Aren Bezuijen (left) and VP Technology Cees Spaans (photo: PAS Publicaties).
wellhead module twice. First with two decks. However, when Statoil decided that it had to be a single-deck module, the design had to be modified. In spite of this change, we managed to achieve the planned fabrication starting date.” What is striking about the wellhead module is that after the drilling is completed, the majority of the module will be dismantled. What remains will be integrated in the new topside. Critical design
Statoil immediately recognized that the design for the Valemon jacket would be very critical. Cees Spaans: “Therefore the company started the verification rather early. This was done by DNV. As a result, their analyses could be compared to ours at a very early stage. The real work for us proved to be ensuring that the jacket did not contain a kilo too much steel.” The design and fabrication of the four hoisting points also proved to be challenging. “This was a very intensive design process, and concerned the largest hoisting points ever cast. We subcontracted the latter to a British company that specializes in this type of work.” We cooperated closely with TNO in Delft with respect to determining the impact criteria associated with a ship colliding with the jacket. TNO has a lot of expertise in this field. Another special aspect was to find a solution for the optimum attachment of the piles to the sleeves on the four corners of the jacket.
Published on Apr 16, 2012
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