The Aasta Hansteen Field was named after a Norwegian painter, writer and early feminist, who lived in the late 19th and early 20th centuries. She was a pioneer and trailblazer, much like the eponymous production system, which, when it comes onstream later this year, will be the first spar to work offshore Norway.

When the Aasta Hansteen spar begins production, it will be the largest producing spar platform in the world.

The Aasta Hansteen development, which lies in the Norwegian Sea approximately 300 km (185 miles) offshore in 1,300 m (4,265 ft) water depth, comprises three gas discoveries—Luva, Haklang and Snefrid South—with combined recoverable reserves estimated at 47 Bcm (1.7 Tcf). Field operator Statoil made the decision to develop the field six years ago, submitting its development plan to the Norwegian Ministry of Petroleum and Energy in December 2012 outlining the scheme that would employ a spar for the first time in Norwegian waters. The ministry granted approval in June 2013, and work immediately got underway.

From concept to construction

Statoil awarded the contract for engineering, procurement, construction and transportation of the hull and mooring systems to a TechnipFMC and Hyundai Heavy Industries (HHI) consortium. Unlike the majority of spars, which were designed for Gulf of Mexico conditions, the Aasta Hansteen spar design had to accommodate more extreme environments and have significantly higher structural fatigue resistance. This was the first time a spar hull was designed and built to NORSOK and other Norwegian requirements. The platform had to be built to survive 10,000-year storm conditions and to be operational in 100-year storms.

The new design also includes an elevator in the moonpool access shaft, 25 Mcm (883 Mcf) of storage for condensate and an offloading system, which places the Aasta Hansteen spar as the first to function as an FPSO vessel. The space requirement for storage combined with the 24,000-ton topside makes the Aasta Hansteen platform the world’s largest truss spar hull at 200 m long (656 ft) and 50 m (164 ft) in diameter, with total displacement of 146,000 mt.

The field development layout comprises a spar platform and two subsea templates with eight well slots. EMAS AMC was awarded the contract to transport and install the two four-slot subsea templates and one single-slot template on the field, all of which were shipped from Aker Solutions’ facility in Sandnessjøen, Norway, on EMAS’ Boa Sub C construction vessel. Another first was achieved with the subsea template installation, which is the deepest on the Norwegian Continental Shelf (NCS).

The subsea templates are tied back to the spar platform through pipelines and steel catenary risers (SCRs). Made feasible by the stable motions of the spar, SCRs are being used for the first time offshore Norway.

Subea 7 was awarded a contract for procurement, fabrication and installation of 18 km (11 miles) of 12-in. mechanically lined pipe flowlines and four SCR systems. Three 2-km-long (1.2-mile) SCRs connect three subsea templates to the spar, with another 2-km-long SCR exporting to the export pipeline system.

The spar hull will be moored onsite using a taut mooring system comprising 17 polyester lines made of Gama 98 polyester supplied by Lankhorst Ropes. The mooring lines are in three clusters—two made up of six lines each and a third with five lines. In yet another first, the lines are being wet stored on the seabed and will be attached to the hull when it arrives on the field.

While the site was being prepared, construction of the spar and topsides was proceeding at the HHI yard in Ulsan, South Korea. Large segments of the spar were constructed on the site in modules that were subsequently lifted as “mega blocks” and mated quayside to the horizontal spar structure using a 10,000-mt crane in an advanced heavy-lift operation that achieved precise mating in five mega-lifts. This was the first time HHI had executed lifting and placement of a mega block of this size.

Moving a mega structure

With the hull and topsides completed, the next challenge was to convey them from Korea to Norway, a distance of 14,500 nautical miles, equivalent to nearly 26,900 km (16,715 miles).

The spar hull made the journey aboard the world’s largest heavy transport vessel, Dockwise Vanguard, owned by Boskalis subsidiary Dockwise. The vessel measures 275 m long (900 ft) and 79 m wide (260 ft) and can carry cargo up to 110,000 mt. When the hull arrived in Norway in June 2017, it was floated off the transport vessel and towed to Klosterfjord, where it was upended and anchored, awaiting the arrival of the topsides.

The platform deck, weighing 24,000 mt, followed the hull to Norway, making the trip aboard the Dockwise White Marlin, the newest and second largest vessel in the company’s fleet. When the topsides arrived at the end of November, it was transferred from the White Marlin to two S-class vessels, which are the smallest in the Dockwise fleet. These units worked as a sort of catamaran, with the topsides balancing across the two hulls as the vessels moved the unit to the hull, where the two massive components were mated. With construction finished, the spar is ready to be moved to the Vøring area of the Norwegian Sea to begin production.

First production from Aasta Hansteen is scheduled for September 2018.

Moving gas to shore

Completed in September 2015, the 480-km (300-mile) Polarled pipeline connects the Aasta Hansteen development to a processing facility on the Nyhamna peninsula, originally constructed to process gas from the Ormen Lange Field, which produces 70 Mcm/d (2.4 Bcf/d) of natural gas. Nyhamna is one of Northern Europe’s largest gas terminals and is getting bigger, having received sanctioning from the Norwegian Petroleum Directorate in February 2017 for expansion. Greater capacity—80 Mcm/d (2.8 Bcf/d)—will allow additional volumes from currently producing fields like Ormen Lange and from future discoveries, which can be tied into Polarled via the six connection points installed along the line.

Embracing innovation

The number of technology advances that were part of the Aasta Hansteen development is impressive. They illustrate how enabling new technologies pushes the boundaries of what is technically possible and changes the status quo. The technologies proven on this development will be the foundation on which the industry builds forward. Projects like this that focus on investing in ideas with the potential to extend capabilities and improve operations will continue to transform the oil and gas industry.

Aasta Hansteen firsts

  • Largest spar in the world
  • First spar offshore Norway
  • First spar with condensate storage
  • First use of SCRs offshore Norway
  • First synthetic rope mooring offshore Norway
  • First time a lift and placement of a mega block of this size were executed at the HHI yard
  • First use of mechanically lined pipe installed using reel-lay offshore Norway
  • First pipeline on the NCS that crosses the Arctic Circle
  • Deepest pipeline on the NCS, reaching 1,260 m (4,100 ft) at the Aasta Hansteen Field
  • First time a 36-in. diameter pipe has been laid at this depth

Also noteworthy are the roles vessels played in the Aasta Hansteen development. The Dockwise Vanguard, the largest heavy transport vessel in the world, carried the spar hull 26,900 km from Korea to Norway, while the White Marlin, the second largest heavy transport vessel in the fleet, moved the topsides. The Allseas pipelayer Solitaire, one of the largest vessels of its type in the world, laid the Polarled pipeline, which connects the Aasta Hansteen Field to facilities at Nyhamna 480 km (300 miles) away.

Comments