The Veslefrikk Jacket Concept

ABSTRACT A new concept for developing oil fields has been prepared by Statoil for the Veslefrikk field in the North Sea. For this deep- water location (174 m) a combination of a semisubmersible production and quarters unit and a drilling jacket is to be used. In the effort to reduce the total cost of the project Statoil propose to minimize the steel weight of the jacket and to install it by lifting. The lifting criteria thus limited the lift weight for the 200 m tall structure to 9800 t which is a challenge for the designers. Aker Engineering was given the task to further develop the jacket and floater. A close cooperation of specialists for lay-out; marine operation and structure design led to a jacket design with the following features. –optimization of the equipment weight–rotation of the derrick skid beam and the deck by 45° relative to the jacket.–reduction of the environmental forces by minimizing the size and the number of the structural elements, and systematic use of the shielding effect.–use of a temporary sledge for the load-out and transport conditions.–cast nodes and lifting trunnions–offshore installed tubular insert in the legs and separate deck support frame. The lift operation is the most critical aspect of the Veslefrikk project. A description of the analysis and the particular requirement of this operation is given. Finally a description of the installation procedure is presented.