Only two platforms were envisaged on Valhall in the original plans (see separate article). But long discussions with the government led to a decision to build three structures – for drilling, quarters and process/compression respectively.
The steel jacket for the PCP had a rather unusual history, and was originally built for use on a small field in the Gulf of Mexico which subsequently turned out to be non-commercial. As a result, the structure was mothballed at the McDermott yard in Morgan City, Louisiana, until Hamilton Brothers bought it for installation on a UK offshore field. But that project also foundered, and the jacket acquired yet another owner – the Ekofisk licence in the Norwegian sector, which intended to use it South-East Tor. This development once again proved unprofitable, so the structure was sold on to Amoco on behalf of the Valhall licence for its own field. The structure was not ideal for the intended production solution, and Amoco was ready to sell it on after the South-East Tor project had been cancelled. But Noco insisted that it be used for Valhall, although it could only carry enough equipment to support a level of production below the final outcome. Amoco maintained that the field should be developed gradually over time, and that so much capacity was not required initially. The “surplus” jacket could accordingly be used. However, it had to be reinforced for use in the Norwegian North Sea. The additional work this required meant that the structure probably ended up costing as much as a new one.[REMOVE]Fotnote: Asbjørn Tansø in conversation with Kristin Øye Gjerde, 16 June 2014.
The jacket was towed from the USA to the Stord Verft yard south of Bergen during August-September 1980 – and this operation proved highly dramatic. A powerful depression had developed over Newfoundland on 16 September, moved east across the Atlantic – roughly along the 50th parallel – and lay west of Ireland on 18 September.[REMOVE]Fotnote: Jostein Mamen, Norwegian Meteorological Institute. This powerful storm parted the towropes. But things went well in the end. The jacket was saved and reached the yard for final adjustments before being placed on the field in April 1981. The platform was ready for final testing by August 1982. Although the conversion probably cost as much as building a new jacket, as noted above, the advantage was that it took less time.[REMOVE]Fotnote: Ministry of Petroleum and Energy, Facts , 1981, 15; Kostnadsanalysen norsk kontinentalsokkel , volume II, 275–277.
McDermott Norge had the main contract for the whole platform, and was responsible for negotiations with sub-contractors. A Norwegian consortium won the job of designing the topside in September 1977. This Valhall Engineering Joint Venture (VEJV) comprised AIS Akers Mek Verksted (41.7 per cent), Brownaker Offshore A/S (25 per cent), Fred Olsen & Co and Kværner Brug A/S (33.3 per cent). Its head office was at Aker Engineering’s Oslo premises, but design work also took place at Kvaerner Engineering in Billingstad outside Oslo and at Brown & Root in London.[REMOVE]Fotnote: Kostnadsanalysen norsk kontinentalsokkel , volume II, 270.
Necessary documentation in the form of calculations, drawings and specifications needed by Amoco for government approval and for its own assessments were to be provided by McDermott Norge. That also applied to the documents needed to prepare bid packages covering the equipment to be used as well as construction and installation of the platform. The packages were intended to provide the basis for fixed-price contracts, with VEJV responsible for assessing the tenders, awarding jobs and receiving deliveries as Amoco’s agent. Furthermore, the joint venture acted as the operator’s consultant during the fabrication phase and carried out assessments on an ad hoc basis.
Oceanic in Brussels, a subsidiary of McDermott Hudson Inc, was chosen as contractor for construction, assembly and installation of the PCP’s module support frame (MSF) and modules. Fabrication work was sub-contracted to three Norwegian yards – Stord Verft (MSF), Vigor in Orkanger near Trondheim (generator module) and Kværner Brug in Eigersund (three compressor modules).
It appeared for a time that France’s UIE would secure the MSF contract, but the Norwegian authorities put pressure on the Valhall licensees to choose domestic suppliers. The companies were called to the Ministry of Petroleum and Energy, where minister Bjartmar Gjerde explained how difficult the employment position was at Stord. No direct order was given to place the contract with this yard, but it nevertheless won the job – to great jubilation at the company, which thereby avoided layoffs.[REMOVE]Fotnote: Aftenposten , 16 November 1979, “500 mill i Valhall-oppdrag”; Bergens Tidende, 16 November 1979, “Stord Verft sikret arbeid i hele 1980”. The MSF and modules were installed on the jacket in November and December 1981, with Oceanic itself handling this job and the subsequent hook-up of the components.
Although the platform was ready on 1 June 1982, its first wells were not completed until 1 October. Oil and gas from Hod began to flow to the PCP on 30 September 1990.[REMOVE]Fotnote: Norwegian Petroleum Directorate, Facts , 2013, 80. Part of the gas was returned to the smaller field for gas lift.[REMOVE]Fotnote: The North Sea Platform Guide, 1985, 690.
Some 650 million barrels of oil (105 million standard cubic metres), 20 billion scm of gas and more than three million tonnes of condensate were produced from Valhall to 31 December 2012. In addition, Hod contributed nearly 60 million barrels (10 million scm) of oil and 1.5 billion scm of gas up to the same date.[REMOVE]Fotnote: Norwegian Petroleum Directorate, Facts , 2013, 80.
The eight-leg steel jacket is 90 metres tall and weighs 5 700 tonnes, including the piles which hold it in position. Including modules, the topsides weighs 9 900 tonnes without liquids on the tanks. Its main dimensions are roughly 61 x 30 metres, with a height of 16.5 metres. In addition comes a 100-metre flare boom, which protrudes from the PCP’s south-east corner at an angle of 45 degrees.
The most important platform components are the following.
For oil processing :
- test separator
- two one-stage separators
- two two-stage separators
- export pumps
For gas processing :
- first-stage compressor
- second- and third-stage compressors (in same housing)
- expansion recompressor
- final-stage compressor
An export compressor was also installed after 2000 to achieve a sufficiently high gas pressure for transport through the pipeline. The process is described in a separate article.