Valhall Flank Water Injection Platform, Norwegian North Sea, Norway

The Valhall field was discovered in 1969 and came onstream in 1982. It is operated by BP (28.09%) on behalf of Amerada Hess (28.09%), Enterprise (28.09%) and Total E&P Norge AS (15.72%). The field lies at 70m water depth.

At project sanction it had 247 million stock tank barrels of oil (mmboe) located in the Chalk reservoir and has been upgraded to 1,272mmboe. The field is due to become operational in 2010. Operator BP is building a new field centre at Valhall due to subsidence and the need to operate more efficiently.

The new centre will consist of an integrated processing and housing platform and will receive power form shore via a 292km-long cable from Lista.

In June 2007, the plan for development and operation (PDO) of the Valhall field was approved. All major contracts except the offshore hock up support and start up preparation contracts have been approved and by February 2009, approximately 40% of the project was remaining for completion.

The Valhall complex consists of five separate steel platforms, all bridge-connected.

Built in 1979, the quarters platform (QP) was put to use in July 1981 with accommodation for 208 people.

Built to process 168,000bbls of oil and 350mcf of gas per day, the production platform (PCP) is situated at a height of 65m and weighs 21,000t.The 2/4-J pipeline at Ekofisk Centre transports the oil produced to Teesside, in England, while direct transportation of the gas is to Emden, Germany, through the Norpipe pipeline. Oil and gas coming from Hod are also processed at the platform.

In April 1996, the wellhead platform (WP) was installed and oil was first produced in June. WP has 19 well slots. It incurred a total cost of NKr1.5bn, including the costs to drill the wells. Drilling of the last few slots was planned to be completed by summer 2002.

Two new projects have been commissioned as part of the field redevelopment: the Valhall flank platforms and the water injection platform.

Valhall flank platforms

Valhall flank platforms (VFP) include two unmanned wellhead platforms (WHP) with 16 drilling slots each. The wellstreams will be processed at these platforms, located 6km from the existing Valhall facilities. They are located at a water depth of 66.7m (South WHP) and 69.4m (North WHP).

Each platform drills about eight wells, one waste injector and seven producers. West Epsilon drilled wells from October 2002 to August 2003 on the South Flank. Production on the South Flank started in May 2003 and the North Flank came onstream in January 2004. Each of these platforms has provision for water injection. The platforms would be powered from Valhall. Operations will be monitored through a fibre-optic cable connected to the existing facilities at Valhall.

Pipelaying for the north and south WHPs was performed as a continual operation during a peak weather window in 2002. Heerema Tonsberg was principal contractor for the WHPs, however jackets were sub-contracted to Heerema in Vlissingen, Netherlands. The pipeline laid is duplex, rating 310barg design pressure.

The 13% super chrome pipeline units specified were welded together by the pipeline contractor Coflexip Stena Offshore at its fabrication site in Orkanger, Norway before being reeled on to a vessel for offshore installation. Tie-in modification work to the Valhall production platform was carried out by Aker.

Water injection platform

Water injection platform is located at a water depth of 73m with an injection capacity of 180,000 barrels of water per day (bwpd). The platform was aimed to improve the oil recovery factor from 31% to 38%. This yields roughly 29,000,000m³ in additional oil. The total investment for the project was NKr7.2bn, including NKr1bn in piling work.

Installed in 2003, the water injection project involved linking a fixed steel platform to the existing Valhall wellhead platform. The integrated topside has water injection facilities, seawater and produced water treatment facilities, and power generation. There is also a platform-based drilling rig, which can skid on beams from the wellhead platform to the wellhead injection platform, including a mud mixing module.

Drilling and maintenance of wells on the new platform (24 wells in total) as well as on the existing WP platform is possible by the configuration of this injection platform. The 4,000t platform was due to be installed by the heavy lift vessel Saipem S7000, however the company had difficulty driving some of the piles securing the jacket to the seabed. Once the piling is finished, the 9,500t topside will be installed.

New field centre

Operator BP is building a new field centre at Valhall due to subsidence and the need to operate more efficiently. The plan for development and operation (PDO) was approved in June 2007. An integrated processing and hotel platform is being developed under the project. A 292km-long cable running from Lista will supply power from shore to the new field centre. All key contracts related to the new field project, pending the one for supporting offshore hock up and start up preparation have been awarded.

The new centre has an oil production capacity of 120mbopd, and can handle gas volume of 143mmscf/day, and has a total liquid capacity of 200mbpd (oil and produced water).

60% of the development activity was completed by February 2009.