Top Tensioned Riser For Innovative Floating Dry Tree Units: Technological And Design Issues And Developments Available to Purchase

Saipem Group, through one of its Companies, Moss-Maritime, developed an innovative concept of floater for dry tree units, named "Octabuoy". Peculiarity of the system is to guarantee a reduced motion, while accommodating on board drilling / workover, production and compression / export facilities. Top Tensioned Risers are envisaged for drilling, production and export purposes. The system architecture of the adopted concept for the Top Tensioned Risers (TTRs) is similar to the one adopted for the TLP units but the requirements in terms of motion and stroke are almost similar to the one experienced in the SPAR units. Moreover, the adopted concept for the TTR is similar, in term of top tension and relative stroke, to the Conventional Hydro-Pneumatic Tensioning Systems, usually installed on Drilling Rigs. The main associated issues are related to the reliability of these systems along the whole design life, and the associated needs for redundancies/possibility to perform the required maintenance, without affecting the production. The system configuration for the TTRs and the accommodation of its main components to be integrated on the Topside, namely the Hydraulic Cylinders, Air/Oil accumulators and APVs, affects the deck layout and the design of the well-bay, the moon-pool, and the drilling / workover rig configurations. Purpose of this paper is to present the selected TTR Configuration for the Octabuoy-based Dry Tree Units, together with the main technological and structural aspects involved in their development and relevant design. In addition, the Octabuoy-based Dry-Tree Unit can accommodate on board conventional steel catenary risers, both for import flowlines from satellite wells or for export pipelines. The Octabuoy hull provides two advantages to the conventional SCR configuration: a lower first order vessel motion, inducing a lower fatigue damage, and a flexibility in the location of the riser hang-off. These advantages are also outlined and discussed within the paper, to give a more exhaustive view of the advantages related to Octabuoy concept, with respect to the overall riser system configuration