Technology from Europe:
Norway/Sweden

Well intervention, service vessel concept based on proven semisubmersible structure

A well intervention and service vessel concept for benign environmental waters has been designed by GVA Consultants, based in Gothenburg, Sweden. Some of the benign areas targeted by this concept are the Gulf of Mexico, Brazilian waters, offshore West Africa and the South Pacific.

The GVA 3500 WISV is built on the firm’s familiar two-pontoon, four-column structure, plus a rigid upper deck box.

Dubbed the GVA 3500 WISV, this design is based on the well known, proven series of GVA semisubmersible units, including the characteristic structural configuration. There are two pontoons, four columns and a rigid upper deck box. Operational displacement is targeted to about 26,000 t.

Station-keeping is accomplished via a fully redundant, dynamic positioning (DP) system. This system will feature two 4.5-MW stern propulsion units, plus two 4.5-MW, retractable azimuth thrusters in the forward area. While in transit, the unit will have a speed of 12 kt.

The unit is configured to carry out well interventions and well services, including well completions and intra-field pipelaying in environmentally moderate regions. Payload and capacities (see table) are adjusted for operation during prolonged periods at sea, where supplies are not frequent. The large upper deck will feature well-arranged working areas and systems tailored to well intervention and servicing. 

Power generation systems are arranged to comply with the DP system’s requirements. Power will come from eight medium-speed, diesel-driven generators, each contributing about 3,500 kW. These generators will be housed in four separate engine rooms that are away from accommodations, to minimize noise.

Basis for design limits of the steel structure and equipment is 100-year Gulf of Mexico weather. This translates to maximum winds of 79.7 knots (91.7 mph or 41.0 m/sec), with a 10-min. mean at 10 m. Significant wave heights are 12.5 m (41 ft), and maximum wave heights are 23.8 m (78.1 ft).