Construction of the Statfjord A

by Trude Meland, Norwegian Petroleum Museum

Casting the gravity base structure (GBS) for the Statfjord A platform began in October 1974. From then until 1976, four of these massive concrete deepwater (Condeep) units were under construction in the Gands Fjord off Stavanger.

— Statfjord A's GBS floating in the dock. The spun wall, which has kept the water out of the dock during the first part of the bottom section's casting, is being removed to allow the platform to be towed into the Gandsfjord for further construction of the GBS. The platforms under construction in the fjord are Brent B (left) and Beryl A. Photo: Norsk Fly og Flyfoto A/S/Norwegian Petroleum Museum

Mobil’s Beryl A and Shell’s Brent B GBSs were moored in the autumn of 1974 out in the deep water of the fjord, while work was under way in the Hinnavågen dry dock on Shell’s Brent D as well as Statfjord A.

The Condeep was a Norwegian design developed by the construction company Høyer-Ellefsen. This company and fellow builder Ingeniør F Selmer A/S won a contract on 13 July 1973 for the very first of these structures. Placed by Britain’s Mobil North Sea Limited for the Beryl field, the assignment also covered mechanical outfitting by the Aker fabrication group.

Construction of the GBS proved very challenging, and the two construction companies joined force with a third – Ingeniør Thor Furuholmen A/S.[REMOVE]Fotnote: Steen, &., & Norwegian Contractors. (1993). På dypt vann : Norwegian Contractors 1973-1993. Oslo: [Norwegian Contractors]. The trio established a joint venture under the name Norwegian Contractors (NC) to handle the building job.

Before ordering the Beryl A Condeep, Mobil had obtained bids from seven different companies offering various steel and concrete solutions for delivery in 1975. The Beryl operator opted for the Condeep after a detailed study of all the bids.

It came out well in price terms, and the NC group had experience of offshore concrete work from building the Ekofisk tank a few years earlier. In addition, the Condeep offered a foundation solution which suited the seabed conditions on Beryl. These considerations offset the fact that the design involved a completely new application of technology. It was a pioneering project.[REMOVE]Fotnote: Steen, &., & Norwegian Contractors. (1993). På dypt vann : Norwegian Contractors 1973-1993. Oslo: [Norwegian Contractors]. Statfjord A utilised a Condeep primarily because Mobil had secured an option from NC for a second GBS, originally intended for Beryl B. When that proved unnecessary, the British arm of Mobil offered its option to Mobil Norway and the Statfjord licence.

Mobil appreciated at the time that Statfjord was to be developed as fast as possible, and the Beryl B option provided a chance to get started quickly. The licensees resolved to seize the opportunity, but were aware that the project was being launched while reservoir information was very limited.[REMOVE]Fotnote: Moe, J. (1980). Kostnadsanalysen norsk kontinentalsokkel : Rapport fra styringsgruppen oppnevnt ved kongelig resolusjon av 16. mars 1979 : Rapporten avgitt til Olje- og energidepartementet 29. april 1980 : 2 : Utbyggingsprosjektene på norsk sokkel (Vol. 2). Oslo: [Olje- og energidepartementet]

Significant changes from the Beryl A solution had to be expected. Those who took the decision also had limited experience with developing such a large and complex structure as Statfjord A, and undoubtedly failed to foresee the consequences of the limited preliminary design work.[REMOVE]Fotnote: Interview with Einar Jensen by Trude Meland, Norwegian Petroleum Museum.