Jeremy Beckman, Editor - Europe
Early this month, Norske Shell was due to take the helm at Ormen Lange in the Norwegian Sea. Hydro, however, has been the project’s driving force since discovering the deepwater gas-condensate giant in 1997.
This September, the NOK50 billion ($9.16 billion) development finally delivered first gas to the UK market via Langeled, the world’s longest subsea trunkline. The production scheme is also wholly subsea, and a future development phase could bring the first deployment of subsea compression on the Norwegian shelf.
Installation of one of the Ormen Lange subsea templates.
Ormen Lange is Norway’s second largest gas field behind Troll, but in much deeper waters – 850-1,100 m (2,788-3,609 ft), compared with 120 m (393 ft) for Troll in the North Sea. It is an elongated structure, around 40 km (24.85 mi) long and 8-10 km (4.97 – 6.21 mi) wide, extending across three production license areas (PLs 208, 209, and 250). The reservoir is around 2,800 m (9,186 ft) below the sea surface, with gas-bearing layers of sand around 50 m (164 ft) thick.
Circumstances forced Hydro to adopt numerous novel solutions for the development. The main issues were the water depths, which were beyond those of any previous development in northwest Europe; the precipitous and rocky Storegga Slide close to the field, which any pipeline would have to traverse; water temperatures of -1°C (30°F) above the reservoir, bringing the risk of hydrate plugs forming in the pipeline; and the need to transport the gas an unparalleled distance to the UK mainland.
Hydro opted to produce the field’s 397 bcm of gas and 182 MMbbl of condensate in phases via up to 24 subsea wells connected to four seabed templates. Produced gas, condensate, and water would be transported from the wells through two 114-km (70.84-mi), 30-in. (76-cm) multiphase pipeline to a purpose-built processing terminal at Nyhamna on the island of Gossen off the mid-Norwegian west coast.
From there, the processed gas would head south through the new 1,200-km (745.6-mi) Langeled pipeline, initially to Statoil’s Sleipner complex in the North Sea, then south-east to another new reception terminal at Easington on the English east coast.
Hydro contracted FKS for front-end engineering design of the subsea facilities, and subsequently also to supply the first-phase subsea production equipment, comprising eight subsea trees and control systems, and two eight-slot, 1,150-metric ton (1,268-ton) templates, the latter being subcontracted to Heerema in Toensberg, Norway. Heerema’s crane bargeThialf installed the templates in August 2005 at separate locations, allowing the drillship WestNavigator to start development drilling two months later. Although Shell assumed operatorship of the production phase, it was also responsible for drilling and subsurface engineering.
Reinertsen performed detailed design of the pipelines. Along the first 20 km (12.43 mi) of the route to Nyhamna, the multiphase lines have to cross the Storegga slide, where water depths plunge from 250 m to 850 m (820-2,788 ft). Saipem’s lay bargeS7000 installed this section of the lines via the J-lay method in summer 2006, with Allseas’ Solitaire handling the remaining 94-km (58.4-mi) portion to Nyhamna via more conventional S-lay. Van Oord then secured the lines by dumping over 3 million metric tons of rock along parts of the route.
TheAcergyFalcon installed the two 6-in. (15-cm) lines injecting MEG into the multiphase lines for flow assurance. Subsea 7’s SkandiNeptune installed the two Nexans-supplied, 125-km (77.67-mi), 4-in. (10-cm) umbilicals – Nexans also trenched these and the MEG lines using its Capject excavator.
Hydro contracted Snamprogetti for engineering of Langeled, with Europipe and Mitsui/Sumitomo supplying the linepipe, and Bredero Shaw the concrete coating. During 2005, Acergy’s lay bargeAcergy Piper and Solitaire laid Langeled’s 552-km (343-mi), 44-in. (111-cm) southern section between Sleipner and Easington. Acergy later installed much of the 626-km (389-mi) northern leg from Nyhmana, the remainder being taken up by Solitaire in 2006. Allseas also laid the landfall stretches at both ends of the route.
Vetco Aibel was responsible for the modification program at Sleipner, which included the installation of new risers in summer 2005. Acergy/Subsea 7 performed the various Langeled subsea tie-ins, with Halliburton conducting pre-commissioning of the pipeline, including de-watering and pressure testing.
This fall Hydro – now StatoilHydro – awarded further contracts for the project’s second phase, known as the Ormen Lange Southern Field Development. FMC will provide a further six subsea trees and a third, eight-slot 1,150-metric ton (1,268-ton) ‘C’ template, to be installed by Saipem in spring 2009. Around the same time, Allseas and Acergy will install two more flowlines and another umbilical and MEG line connecting the new template to the A template, in water depths of around 900 m (2,952 ft). AGR will cut trenches through the rugged seabed for the lines using its Claycutter X system.
As more wells come on stream, some form of offshore compression will eventually be needed to offset declining reservoir pressure. Rather than install a 25,000-metric ton (27,557-ton) compression platform, the partners are hoping to implement subsea compression, which could halve both future development and operating costs.
In March, the partners committed to a NOK2.5 billion ($458 million) pilot project for a subsea compressor station, with Aker Kvaerner Subsea (AKS) and FKS contracted for front-end engineering design. The plan is to test a full-size pilot plant at Nyhamna in 2009.
This will comprise four compressor trains, one to be placed in a water-filled reservoir measuring 30 m (98 ft) long, 20 m (65.6 ft) wide, and 12 m (39.4 ft) deep – this area was blasted out during development of the processing facility.
The partners will decide on a platform or the subsea option in 2011, probably followed by installation in 2015. The compressor station would be placed between two of the templates, covering a seabed area of 60 m x 40 m (197 ft x 131 ft). Each compressor module would likely weigh around 200 metric tons (220 tons), and the station’s 52 MW capacity would be supplied through a submarine cable laid directly from Nyhamna.
