The lifetime extension of the oldest oil field in the Danish North Sea marked one of the most challenging and complex offshore campaigns initiated by Maersk Oil. The goal of the project as a whole was to extend the lifetime of Dan Bravo until 2042.
70 years of accumulated lifetime for Denmark’s first producing offshore oil field
The Dan Bravo field was discovered in the ‘70s and is located app. 200 km (125 miles) west of Esbjerg. The facility consists of a production platform – Dan B, two wellhead platforms – Dan A and D, and a flare platform – Dan C.
Typically, operation life for an offshore platform is limited to 25 years, but with comprehensive studies and calculations the structure can be reinforced to perpetuate the production process for a number of additional years. With this project, the accumulated life of Dan Bravo could reach up to 70 years.
Structural reinforcement of jacket legs
Ramboll was contacted by Maersk Oil to help with the process of prolonging the platform life until 2042. Most of the work targeted the wellhead platform Dan A. Rationalisation tasks included global and local FE analysis (ROSAP, Ansys, LS-Dyna), design of reinforcements, installation/removal procedures and help with tender materials for diving contractors.
After the thorough global and local jacket analysis on Dan A, it was concluded that the best solution was to remove two conductor support levels and reinforce the platform by installing a new one together with multiple K-joint clamps. Thanks to an impressive subsea photogrammetry campaign initiated by another contractor, the design of the new conductor support level and reinforcement clamps could be determined with accuracy.
Unique installation process offshore
The development of the design lasted for app. two years, and since the subsea installation process was entirely carried out by divers, the level of precision was vital.
In order to safely handle the heavy reinforcements above and below water, two temporary cranes were built and clamped onto the vertical members of the platform 12 meters (40 feet) above sea level. They were used together with another two cranes that the diving contractor already had on its offshore fleet.
With a scenario of such complexity, the communication between personnel on boat, rope workers, divers and the dive supervisor had to be coordinated perfectly in order to place the 3 metres wide and 8 metres long heavy steel structure of the new conductor support level and the K-clamps as well. In this sense, Ramboll created a number of interactive animations for the installation procedure that were used as a reference for the preparation of the divers.
Overall, the reinforcement campaign comprised installation of 136 tonnes of steel over 200 days of diving. In addition, 2400 bolts were used to fasten the reinforcements to the Dan A jacket structure.