Semar has been involved in the design, verification and installation of suction anchors on various projects. On the design level, Semar has worked in close cooperation with geotechnical companies such as NGI and has gained experience and understanding of the mechanics surrounding behavior of suction anchors when in place. Design is also supplemented with a constant focus on ease of transportation, installation and removal. With such experience, our engineers are also contributing in fabrication phases at which dimensions and tolerances can affect the operational properties of the anchors.
Projects
› NGI/Equinor – Beacon Wind Suction Bucket Trials – Detailed design of suction buckets – 2022-2023
› Haven at Johan Sverdrup – Design of footings for Haven – 2016
› ENI Goliat – Fabrication follow-up of suction anchors – 2012
› Blind Faith – Suction anchor design – 2008
› BP Skarv FPSO – Suction anchor design – 2007
› Gjøa – Suction anchor design – 2007
› Statoil Kristin – Suction anchor design – 2004
› Statoil Åsgard B&C – Suction anchor design- 1997
Areas of competence
› Suction anchor design developed in cooperation with partners
› All design conditions considered, operation and temporary
› Structural design of the suction anchor including padeyes and outfitting.
› Global capacity of the suction anchor for the governing mooring line load
› Global buckling of the anchor during installation and extraction
› Local analyses of the main padeye
› Local analyses of the lifting padeyes
› Fatigue analyses
› Transportation and handling analyses
Master Marine AS has been awarded a contract by Statoil ASA to provide accommodation services on the Johan Sverdrup field by using the Haven accommodation jack-up. With deeper water and difficult soil conditions on Johan Sverdrup, modifications to the legs and the footings are required. The footings need to be replaced by larger and deeper footings in form of Suction Caissons (SC).
As part of the assessment of Haven as a potential accommodation vessel on Johan Sverdrup, Semar participated in the feasibility and pre-engineering phase. Due to the challenging soil conditions identified during surveys by Fugro/NGI and requirements for overturning stability of the unit, a tricell design has been developed for each suction caisson. Installation is performed by applying suction pressures in the tricells, allowing improved control in penetration and tilt. When in-place, the stability of the tricell is rely on the ability to resist the differential pressures. Their removal can be performed by reversing the installation process, applying overpressure.
As a subcontractor to Master Marine AS, Semar was responsible for the basic design of the SC working in cooperation with NGI (Norges Geotekniske Institutt) and GustoMSC. During the project, Semar fully utilized experience gained on suction anchor design, marine structure design and large floating structure handling. The previous cooperation with NGI allowed the design team to understand and identify structural and geotechnical challenges to be overcome. In the design project involving three different companies, Semar was able to operate in project-level teamwork and display multi-discipline competence from feasibility to basic design to deliver solution fitting to clients and class requirements.
Scope of work summary
› Development of leg extension method and conceptual design of suction caissons and gravity base foundation
› Suction caissons basic and detail design including operational conditions (with soil conditions), static stress and buckling analyses in accordance with DNVGL rules
› Hydrostatic and hydrodynamic analyses of the suction caissons and the completed vessel
› Evaluation of pitch damping during towing by CFD
› Production of structural design drawings issued for construction
› Development of marine operation philosophy and procedures
› Support during construction
Key figures
Client: Statoil ASA / Master Marine AS
Operator: Statoil ASA
Project duration: 2014 – 2017
Total contract size: 100 millions USD upgrade cost
Project characteristics: 115m water depth, 4x2000t footings, tricell footing type with 13m diameter cells, 25m footing height (19m skirt height)