Installation of reeled rigid pipelines connected to large and heavy subsea structures in ultra deepwater

摘要

The PDEG-B installation scope comprised 165km of X-65 pipelines in water depths up to 1400m with 15 end and in-line structures, some of which were the largest ever launched from the reeled pipelay vessel Skandi Navica.rnThe larger structures (Pipeline End Manifold Y pieces) weighing more than 40te had dimensions exceeding the limits of the lay ramp structure handling frame normally used for standard structure handling onboard the vessel. A special frame was designed and attached to the aft end of the pipelay vessel's ramp to secure the structure during pipelay initiation. This proved to be a suitable arrangement for the deployment of large and heavy pipeline end manifolds. Three large In-Line-Tees were also installed in water depths up to 1052m. Specific facilities for installation of the mentioned sub sea structures were developed, e.g. inclined base to suit the seabed profile, articulated yokes to allow the deployment and landing, attachment of buoyancy elements to reduce the level of stress on the pipeline, development of a contingency procedure to guarantee the structures' upright stability etc. Special attention was dedicated to the scenario of deepest section of the 12" pipelay (>1250m). The new Subsea7 Pipelay vessel, Seven Oceans, performed the deployment of 22km of pipeline that would exceed Skandi Navica capacities.rnThe purpose of this paper is to present all relevant aspects of the successful installation of the structures not only restricted to their design, but also focusing on the modifications to the pipelay Vessel and offshore operations during the PDEG-B project.