A single-column floater (SCF) concept aimed at the Norsk Hydro-operated deepwater Ormen Lange gas field will break new ground for the Norwegian sector if its design is accepted.

Engineers at ABB have put the design - essentially a spar - forward for use on the North Sea gas field knowing that their platform design will have to withstand some of the worst marine conditions found anywhere in the world.
ABB's SCF is designed to withstand 131-ft (40-m) waves - the sort of significant wave height that can be expected to hit a North Sea facility once every 100 years. Gulf of Mexico significant wave heights are put at only 26 ft (14 m) for comparison. Although the development of a wave that big in the North Sea is remote, engineers nevertheless must design the platform to withstand the colossal volume of water that such a wave might bring.
To overcome this, the Ormen Lange SCF design features an extensive air gap between the SCF column and the deck and topsides - allowing large volumes of water to wash through the lower parts of the facility rather than overwhelm them.
The SCF also features a greater draught to provide stability and strakes to avoid vortex induced vibration (VIV), but engineers still must overcome what ABB calls third-phase vibration - induced in other parts of the SCF design by the VIV strakes themselves.
"They (Hydro) have gone away from a solely subsea compression solution," said Rune Strømquist, ABB's senior group vice president for oil and gas technology.
Norsk Hydro appears close to a concept selection for Ormen Lange, and a final decision is anticipated by December.
If Hydro opts for an offshore production solution for Ormen Lange, ABB's SCF could be the largest example of the design to be built, although it has been developed for much smaller field applications as well.
Statoil's Norwegian-sector North Sea fields in the HaltenBanken and Tampen areas present similar harsh environment challenges and will require equally robust structures to withstand extreme wintertime wind and wave conditions. These include Svale and Skirne.
Earlier this year Hydro indicated it was moving toward a floating or fixed offshore platform concept for Ormen Lange as opposed to tying the field back to shore.
"Offshore development is still considered the most viable development concept by the Ormen Lange unit. However, Nyhamn in Aukra municipality is considered the most suitable landing site for Ormen Lange if the gas is to be landed. Nyhamn will be fully evaluated against the preferred offshore development in late 2002," the operator indicated earlier this year.
Ormen Lange is a 14 Tcf gas prospect. Saipem's Scarabeo 5 drillship completed a fifth appraisal well earlier this year to firm up the reserve estimates. Production levels of between 494 Bcf/year and 706 Bcf/year are sought. The field crosses four Norwegian blocks, 6305/4, 5, 6, and 8, and was discovered in 1997 with the 6305/5-1 well. Ormen Lange has since been ascribed the title of the second largest gas field in Norway after Troll.
The challenge of developing the field is not just the water depth - which varies from 2,624 ft to 3,936 ft (800 m to 1,200m) - but the nature of the seabed in the region of the field location, about 87 miles (140 km) west of Kristiansund in mid-Norway. The underwater topography is famous for the Storegga slide - a region of unstable seabed created 7,000 to 8,000 years ago at the end of the last Ice Age, possibly triggered by a major earthquake.
For Norsk Hydro and its partners, the challenge will be to provide a development solution and pipeline export route that accounts for potential seabed movement.
Four major options have been developed. One is a moored spar with 10 wells and a pipeline to shore - which ABB likely hopes is the final choice. Another is a subsea template tying the 10 wells direct to shore. Option three is a total subsea completion tied back to shore with 16 wells. A fourth option is for 12 wells exporting to a concrete platform and the onshore gas terminal at Kollsnes, Norway.
Extensive seismic surveys have mapped the seabed, while core samples and geotechnical surveys also have been carried out to inform project plans.
The goal is to establish the stability of the Storegga area, identify mechanisms that can trigger mud slides and evaluate the risks of further slides. Surveyors also are assessing the possibility of reservoir subsidence during production.
Whichever scenario is chosen, Hydro aims to have Ormen Lange onstream by 2007, when Shell is due to take over as operator.

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