Nexans innovative Spider dredging system, levels the seabed at depths of 1,000 m before laying cables
Nexans innovative Spider dredging system, levels
the seabed at depths of 1,000 m before laying cables
Nexans has developed a new steep terrain dredger/ sub-sea intervention vehicle for the demanding seafloor terrain of the Ormen Lange gas field on the Norwegian continental shelf.
The Ormen Lange is a pioneering project, with Hydro as operator. The field lies in an area of the Norwegian Sea with rough seafloor and climatic and oceanographic conditions that render it one of the world's most demanding gas development projects.
OTC Houston, May 2, 2005 - Nexans, the worldwide leader in the cable industry, has developed an innovative terrain dredger/sub-sea intervention system, called the Spider. The Spider is the only technology capable of levelling the seabed in steep areas. It combines powered tracks, with an articulated walking leg system, enabling it to function in very uneven sub-sea terrain with up to 35 degrees slope. The Spider is derived from the well proven Capjet trenching vehicle design and benefits from more than 15 years of experience in sub-sea vehicle design and operation.
A combination of advanced technologies
The Spider incorporates an advanced control system and is built to work in water depths of approximately 1,000 m. The Spider's movements are controlled by operators located aboard a support vessel, where they operate all movements via a specialized Launch & Recovery System or LARS. Power and signals between the vessel and Spider are supplied through an umbilical (designed and supplied by Nexans).
During operations, the operators follow the Spider's movements via underwater cameras. However, when material stirred up from the sea bed reduces visibility, an alternative is provided by a virtual three dimensional computer image. This virtual image of the seabed is prepared by the onboard survey operator and loaded into the Spider's data system. Once the operation has started, new terrain surveys are performed as required to confirm the seabed profiles.
The new Capjet development
Standard Capjet trenchers trench cables and pipelines into the seabed and cover them as they travel along the cables and pipelines. Specialized swords with water jets break up the soil thus creating the trench.
The Spider has a different task, which is to level or flatten out the seabed in one particular area using a combination of water jetting and suction to remove large volumes of soil. This is done by using a dredging head on an extendable arm to cover the operational area. The telescopic tool arm can also be equipped with purpose designed dredging heads, cutting tools and other intervention tooling.
Many major design elements are derived from the Capjet technology, while the Spider wheels/legs, telescopic arm and slewing are further developments of an advanced forest harvester system (Menzimuck). Nexans has purchased all offshore rights for sub-sea use of this system.
The Spider - specially developed for the Ormen Lange project
In order to find the appropriate solution for a very demanding seafloor terrain, Hydro, the operator of the Ormen Lange Field, contacted Nexans in 2002 to discuss possible means of leveling the steep and uneven seabed of the pipeline and flowline routes. Several different possible modifications of the existing Capjet design were discussed, and Nexans came up with a radical new proposal leading to the development of the Spider technology.
The principle design of the Spider unit was developed by Nexans' engineers in Norway, with support from several specialized vendors and suppliers. It also required close cooperation with a Norwegian company, GTO, which has developed subsea ejector based dredging technology. This technology has been incorporated into the Spider design. Finally, the machines were constructed at the Nexans Halden plant in Norway, before it was mobilized to the vessel.
The first Spider was constructed and tested in the Ormen Lange field in 2004. After a period of testing in the Kristiansund area in Norway, operations have now started for the Ormen Lange project and will continue throughout the summer season this year. Since inception the Spider has been continuously improved. A new, more powerful, version is now operational. Currently, both Spiders are mobilised on the same vessel to increase dredging capacity.
In addition to levelling operations, the Spider dredgers can also be used as general sub-sea vehicles for a variety of sub-sea intervention tasks, and Nexans is developing new markets in these niche areas.
Moreover, since the Spider is based on Capjet technology and equipment, it is possible to convert it to a normal Capjet trenching unit to strengthen Nexans' future capacity in the trenching market.