Statfjord C project kicks off

The biggest change was that the C platform was dimensioned to produce 210 000 barrels per day (b/d), compared with 180 000 on Statfjord B.

   The most visible change was the helideck, which was elevated to avoid the wind forces and turbulence created by the drilling module on Statfjord B. Because the helideck on the latter was below the level of other structures, helicopter traffic to and from the platform had faced problems.

   When the wind was in a certain direction and stronger than a stiff breeze, flights could neither land nor take off. So the Statfjord C helideck rose high and free above the rest of the topside, as if on stilts.

   The size of the living quarters was also increased, from 200 berths on the B platform to 272. This was achieved by placing an extra storey of cabins on top, and moving the stairwells to the sides. An additional storey for ventilation equipment was installed above that again.

   This meant that the net weight to be borne by and on the steel module support frame (MSF) was increased by 1 000 tonnes. The latter accordingly had to be reinforced.

   In addition, a good deal of equipment proved redundant as long as oil production was to be exported by shuttle tanker rather than pipeline. It was resolved in 1980 that the loading buoys and tankers would serve as the permanent transport solution for the field’s whole producing life.

   Seabed conditions at the northern end of the field, where Statfjord C was to be installed, were firmer than further south. This meant that the bottom of its gravity base structure (GBS) did not have to be as large as it was on B – 14 000 square metres compared with 18 000. The design of the steel skirts under the base was also amended.

   Since the plans called for a larger production capacity, the diameter of a number of pipes had to be increased. At the same time, the tanks for separating gas from oil were provided with new internal equipment to boost their efficiency and extended by 0.5 metres.

   Another type of gas dewatering facility was also specified. This involved a contractor pump to remove water from the gas with triethylene glycol, instead of injecting glycol into a heat exchanger. A large separator was installed to remove droplets from the gas for flaring off.

   The bulk of the gas was to be piped to the A platform through a 20-inch flowline with the necessary compressor and other systems. Additional equipment made it possible to increase water injection rates to 296 000 b/d – and actually as high as 350 000 b/d if necessary – compared with 272 000 b/d on Statfjord B. In addition, ballast pump capacity was expanded. But the main structure and most of the equipment were indeed copied from the B platform.

   The official approval given for Statfjord B also applied to the C platform, and the concept for the latter was approved in a letter to operator Mobil on 24 December 1980.

   To learn more, see: Building Statfjord C