Rough, uneven seabed terrain
The project, headed by Statoil, will involve pipeline installation at water depths reaching 1265 metres, setting a world record for deep water installation of a 36" pipeline. The pipeline will be laid through very uneven terrain where ancient icebergs has been scouring the sea bed leaving behind numerous of free spans of up to 200 metres. The pipeline will be installed empty on the uneven seabed and flooded shortly after.
Rectifying free spans
Detailed analyses of the entire route have revealed approximately 85 locations where the pipeline loads would exceed allowable loads due to free spanning. For these locations we have assessed how seabed intervention could most efficient be made - either removal of peaks and shoulders by dredging, or installation of rock support in the free spans.
The result is that a large number of both supports and dredging of peak and shoulders is required.
Ramboll will provide offshore engineering assistance onboard a specialized vessel rectifying the seabed. The offshore work will be performed in water depths ranging from 87 m to 460 m.
The pipeline installation will commence in 2015 where one of the largest pipelay vessels Solitaire will install the Polarled pipeline starting at the Nyhamna terminal. For the initial section in Bjørnsundet counteracts will be installed enabling laying in curves with low lay radii (1.0 – 2.5 km).
The Polarled pipeline's route lies within the narrow strait of Bjørnsundet, parallel to existing subsea pipelines. This requires specialised route designs, including the use of turn points allowing the route to follow the overall contours of the strait. Some of the temporary installed turn points have to be installed on pre-lay foundations.
Pipeline subsea structures
The geotechnical design for the subsea structures comprising five inline tee assemblies and the Polarled PLEM (PipeLine End Manifold) has also been demanding due to the soft clay. The geotechnical analyses have included 3D geotechnical modelling used to optimize the design.
As part of the geotechnical design, earthquake analyses have been performed for 100 year and 10000 year earthquakes to assess the settlements.
Ramboll carried out an assessment of the tie-in operation using remotely operated tie-in equipment.
In addition Ramboll provided:
HSE management including hazard identification seminars and Quantitative Risk Analysis
Interface coordination against Aasta Hansteen project, Nyhamna expansion project, connecting pipeline projects and various contractors
Assistance to Statoil for preparation of Environmental Impact Assessment for the offshore pipeline part (2012).
Multidisciplinary project team
The pipeline engineering services is performed by Ramboll's Copenhagen office, with valuable assistance from our offices in Norway and India.
Ramboll will be working on the detailed design and follow-on engineering for the project until the end of 2016.