The Aasta Hansteen FPSO spar is a Spar gas platform designed by Technip-USA, currently being built by Hyundai Heavy Industries in South Korea. Once complete it will be transported on its side on board the Dockwise Vanguard Heavy Transport Vessel (HTV) to a fjord in West Norway. The Spar hull will be upended in the fjord, topsides installed using floatover technique and then towed vertically to the Aasta Hansteen gas field 300 km off the coast of Norway. The spar will be tethered north of the Arctic Circle using polyester moorings to the seabed 1300m below. At a height of 198m (of which 177m will be submerged) and diameter of 50m this will be the biggest spar platform hull ever built in terms of diameter and displacement. The spar hull will be a Truss Spar type allowing condensate to be stored in the hull beneath sea level and offloaded to a shuttle tanker. The produced gas will be exported to the shore with rigid Steel Catenary Risers (SCR). The Production import risers will also be SCRs, first time of application of SCRs in North Sea.
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Design
Once on site it will be partially submerged by filling ballast tanks to 177 m and anchored to the seabed, leaving only the top 21m above the surface. The seabed moorings will be primarily made of cut resisitant polyester and steel chain.
The Aasta Hansteen spar will export the natural gas from the field through the yet to be built Polarled pipeline to the Nyhamna processing plant on the Norwegian coast.
Aasta Hansteen gas field
Originally called the Luva gas field and later renamed after Aasta Hansteen, it was discovered in 1997 approximately 300 km off the coast of Norway. During start up of the platform, the production from the surrounding Luva, Haklang and Snefrid gas fields will be exported to the platform. Future fields already discovered are planned to be tied back to the Aasta Hansteen platform through SCRs. Future expansion of additional risers and topsides facility are built-in in the design of the platform. The field is located north of the Arctic Circle, and is subject to perpetual darkness and sub-zero temperatures in the winter months.
Transport
The Aasta Hansteen spar will be built on its side in the Dry Dock on barges. Once built it will be floated off the barges and then floated onto the heavy transport ship, Dockwise Vanguard and shipped to a fjord in West Norway. The Vanguard will then be partially submerged allowing the spar to be floated off the ship. The Spar will be upended in the fjord and towed vertically to the Aasta Hansteen field and anchored to the sea bed.