DP drilling platform
Like the other Valhall platforms, the drilling installation was built at a number of different yards. Aker Verdal was commissioned to fabricate the steel jacket, with the topsides originally due to come from Kværner Egersund. When the latter secured the contract to build part of the Statfjord B topsides, however, Amoco became concerned that this could affect progress for the Valhall project and the job of completing the DP topsides was shifted to Verdal. Egersund nevertheless prefabricated parts of the topsides and the bridge to the QP. The four-module topsides came from Stord Verft, while the three drilling modules were fabricated by Kristiansands Mek Verksted.
The platform was ready for drilling to start – with the North Sea’s first enclosed derrick – on 17 December 1981.
However, the initial wells did not proceed entirely as planned and it took almost 10 months to get the field on stream. The last well from the DP was drilled in 1996, in the same year that a new wellhead platform was installed. Removal of the derrick did not take place until June 2009.
The eight-leg steel jacket stands 90 metres high and weighs 7 900 tonnes, including the piles holding it in place. Put together from modules, the topsides weigh 7 300 tonnes in all, measure roughly 54 by 30 metres and are 23.5 metres high. In addition to the derrick come three drilling modules, and space is provided for 24 well slots. Six additional slots were installed between the original set in 1989. A large cranes is installed roughly midway on each long side. The DP is linked both to the PCP and the QP by two bridges, each 45 metres long.
The most important equipment components on the DP include:
- Storage tanks for drilling mud
- Mud treatment facilities
- Tanks for fluid to be pumped down under high pressure to fracture the reservoir rock
- Ventilation equipment
In addition to drilling wells, the DP is the point where the wellstream – containing both gas and water as well as oil – reaches the surface. This is transferred to the PCP through pipes attached to the bridge linking the two structures.