The worlds largest CONDEEP, Gullfaks C, will be installed in the North Sea this summer. During 3.5 years of design and construction work, there has been a number of developments with regard to construction and offshore technology. These improvements will be of significant importance for the development of the next generation of concrete offshore structures for water depths of 300 m and more, and for extreme environmental conditions as those present in the subarctic.
After a short introduction to the Gullfaks C platform, this paper gives a survey of four of the technical improvements achieved during the project, i.e.
Development of the concrete pumping technique for distribution of considerable concrete volumes over great length and height.
Application of a modified rock-anchor type prestressing tendon as a passive anchor.
Rationalization of ordinary reinforcement by application of T-headed bars as confinement in highly congested areas.
Further development of Tubular Bearings as Self adjusting load-transition elements between the deck and the concrete base structure.
The Gullfaks Field, Block 34/10 in the Norwegian sector of the North Sea, is located about 160 km west of the Sognefjord on the west coast of Norway and about 20 km south-east of the Statfjord Field.
The fields recoverable reserves have been estimated to 210 million tons of oil and 29 billion Sm3 of gas and have an expected production period of 20-30 years.
Licencees are Statoil with 85%, Norsk Hydro with 9% and Saga Petroleum with 6% share.
The Gullfaks C platform is the last CONDEEP in a series of three ordered by the operator Statoil for the Gullfaks Field, and by far the largest one ever built, see Fig. 1.
The platform is of the PDQ-type, containing Process and Drilling installations as well as living Quarters which can accommodate up to 300 people. The weight of the deck is at mating approximately 49000 tons and during production 55000 tons.
The Gullfaks C Gravity Base Structure is of the type CONDEEP 4/24T, which means that it consists of 24 cells with 4 shafts in a T-configuration, see Fig. 2.
The total height of the concrete structure, from tip of skirts to top of shafts, is more than 260 m, giving the platform a total height of about 370 m. The base area measures more than 16000 m and each of the 24 cells have an inner diameter of 28 m. The shafts rise more than 160 m above the caisson and are constructed with variable diameter and wall thickness.
The platform is to be placed on 216 m of water depth on very soft soils. Mudline horizontal force and moment due to environmental forces adds to more than 700 MN and 65000 MNm respectively.
