Dynamic behavior of prototype risers, umbilicals, and mooring systems for deepwater use is normally analyzed on computers or on scaled-down models in test basins. These trials can never provide a true picture, however, as no facility is equipped to simulate actual winds, waves, and currents simultaneously. The same applies to deepwater lifting and acoustics systems. Positioning behavior is not truly replicable in shallow-water conditions.
Three closely linked companies in the Marseille/Toulon region are proposing an alternative solution – a locally-based, full-scale offshore test site. Authors from AUV specialist Cybernetix, diving group Comex, and oceanographic research center Ifremer outlined their proposals last November at the Deep Offshore Technology Conference.
Benign conditions
Within a few miles of the Marseille-Toulon coast, water depths dip sharply to 2,500 m. The climate in this part of the Mediterranean normally allows over 300 days of easy sea operations per year, interrupted occasionally by a stiff wind blowing from the north known locally as the "Mistral." Marseille and Toulon both have giant industrial harbors. Ifremer, based just west of Toulon, operates a fleet of deepwater semisubmersibles, ROVs, and AUVs, while the French Navy also maintains three underwater research centers in the area.
Additionally, there are two existing deep-water test sites in the region, although neither has yet been used for offshore developments. Antares, an "underwater telescope" project, is based 10 km south of an island offshore Toulon, in 2,400-m water depth. Facilities available here include a 40-km subsea power/communications umbilical connected to a control station in La Seyne, a subsea power module with connectors that can be mated by ROV, and a permanent long baseline array offering positioning accuracy to within 2 m over a range of 5 km.
The other site is in Villefranche, west of Nice, where the Navy operates three permanent acoustic bases in water depths from 300-2,400 m.
On land, complimentary facilities for offshore testing include Comex's hyperbaric center in Marseille, the BGO First wave test pool in La Seyne, and acoustic laboratories in Marseille, Nice, and inland in Aubagne.
Based on a two-year survey among potential customers of the Deep Offshore trial center (offshore operators, subsea equipment manufacturers and underwater engineering contractors), the three companies driving the project compiled specifications for the future complex. These included:
- Water depths ranging from 500-2,500 m
- Provision of 25 KW of power on the seabed
- High-speed seabed communications
- Video, positioning, and acoustic noise facilities.
Marine support
Aside from subsea construction vessels, associated marine support would include a 3,000-m depth-rated ROV, 100 sq m free deck space, 10-tonne lifting facility, and DP capability in sea state 4.
The range of trials that might be conducted includes functional tests for valves and sensors; performance tests for underwater vehicles and associated tooling; endurance for wet connectors and actuators; robustness for acoustic modems; qualification programs for subsea process equipment; and pipe connection/repair procedures.
The trial center trio also considered erecting a mobile test site for re-deployment in different locations in order to match the required water depth. This would comprise a surface buoy (including high frequency communications shore link), DGPS positioning, USBL system, power generation (diesel generating set), and a mooring system for use in depths from 500-3,000 m, equipped to transmit power and communication to the seabed.
Water depths at the location of the proposed deepwater trial center dip to 2,000 m 25 mi from shore. Onshore, there is a wide range of subsea engineering expertise to tap into.
null
The anchoring system would incorporate wet connectors for the same application, and for monitoring equipment such as video, hydrophones, temperature and salinity sensors.
Logistics and DP support vessels would be sourced locally from bases in Marseille and Toulon. ROV interventions without support vessels could be conducted in time with the Swimmer underwater vehicle, currently under development by Cybernetix and Ifremer.
Equipment would be completed by a shore-based station, providing data storage and processing (collected through the HF link), remote operation of the buoy, and maintenance of the various components.
While most of the components described above are currently operational, the mobile test site is still in its design phase, and regional funding is being sought for its manufacture and establishment.
