Floating Production Storage and Offloading vessels, or FPSOs, are offshore production facilities that house both processing equipment and storage for produced hydrocarbons. Moored in place by various mooring systems, FPSOs are effective development solutions for both deepwater and ultra-deepwater fields. A central mooring system allows the vessel to rotate freely to best respond to weather conditions, or weather vane, while spread-mooring systems anchor the vessel from various locations on the seafloor.
Projects
› DOF/ENI – Ivory coast – Baleine 1 and 2 – Mooring pre-installation and FPSO and FSO hook-up – 2024
› DOF – Yinson FPSO – Ghana – 2016-2017
› DOF – Gina Krog STL Buoy – 2014-2016
› DOF – Goliat FPSO – 2011-2015
› DOF – Knarr FPSO – 2014
› DOF – BW Chinguetti – 2013
› APL – Reliance STP Buoy – 2008-2009
› Bergesen Offshore – Chinguetti – 2004-2005
› Bergesen Offshore – Berge Okoloba Toru – 2004
› Bergesen Offshore – Sendje Berge / Sendje Ceiba – 2000-2001
Areas of competence
› Concept development and outline of method statement
› Mobilisation and Operation Procedures
› Hydrostatic and hydrodynamic analyses
› Structural design of grillages and installation aids
› Fabrication co-ordination and follow-up
› Marine operation
› Suction anchor installation
› Pre-installation of mooring lines
› Tow-out and hook-up
The Goliat Field is located in the Barents Sea, north of Norway. The oil discovery was made in the area of PL229 in 2000, a drill license which belongs to ENI Norge AS by 65% and Statoil by 35%. ENI Norge AS, as the field operator, contracted DOF Subsea to carry out the installation work of the Goliat FPSO. As a sub-contractor Semar AS supported DOF Subsea with engineering, project management and installation work. The scope covered installation of 14 suction anchors (Ø7m x 15.5m) with mooring lines and the hook-up, pre-tensioning and positioning of the FPSO on the field.
As a subcontractor to Dof Subsea, Semar was responsibile for the installation of 14 suction anchors, bottom chains, fibre ropes, mooring buoys and top chains. Semar was also responsible for the tow to field and hook-up of the FPSO. The project, contracted to approximately 1 billion NOK, had its administrative center in the Semar office. The management of the project included 10 vessels and 250 people.
The Goliat FPSO (Floating Production Storage Offloading) unit is a Sevan Marine design. A cylindrical platform with a shaft diameter of 90m, main deck is located 44m above bottom line and the process deck located on 50m a.b.l.
The mooring system is divided in 3 clusters, all with different distance to the anchors. The build-up of the lines are different for each cluster as well, and two of them have 4 lines and one have 6 lines. 2 clusters have a buoyancy element in the mooring lines, hence the length of the line segments varies as well. The mooring chain have a diameter of 165mm and the fiber rope segments a diameter of 295mm. Total length of chains is aprox. 8500m and fiber ropes aprox. 12000m. The weight of one suction anchor is aprox 155t.
Water depth on FPSO location is 380m. The mooring winches have a pulling capacity of 450t, and the pre-tension in the mooring system after installation was in a range of 140t to 280t. The MBL (Minimum Braking Load) of the mooring line segments are 2680t (Chain R5) and 2530t (Rope). All components of the mooring system was transported and stored @ Polarbase in Hammerfest as a part of the work scope. The fabrication of the suction anchors was also a part of the work scope, and was sub-contracted to Ruukki Engineering in Finland. The rest of the mooring system was CPI (Company Provided Items).
Scope of work summary
› Pre-installation of 14 suction anchors and bottom chains.
› Pre-installation of fibre ropes, mooring buoys and top chains.
› Temporary mooring inshore Hammerfest.
› Tow to field and hook-up of FPSO.
› Project management
› Concept development and outline of method statement
› Design basis and premises
› Hydrodynamic analyses
› Structural analyses
› Design engineering, preparation of reports, specs & procedures
› 3D modeling and drawing production
› Fabrication co-ordination and follow-up
› Mobilization and demobilization of system and equipment
Key figures
| Client: | Dof Subsea Norway |
| Operator: | ENI Norway |
| Project duration: | 2011 – 2016 |
| Project characteristics: | First FPSO to be installed in the Barents Sea. Polar climate. |
| Goliat FPSO: Approx. Ø100m and height 80m. | |
| Suction Anchors; Ø7m, height 15.5m. Weight: 155t. | |
| Bottom chain Ø165mm. | |
| Fibre ropes Ø295mm. |