Diamond wire cutter enables slicing the legs off oil rigs below the seabed for relocation

Brussels, 29 Jun 2004

The SBC diamond wire cutter makes it possible to slice free underwater structures – such as oilrigs and wellheads – below the seabed, using a novel minimal-disturbance technique. This avoids contamination and damage to the seabed, and rigs can be re-used.

Much of the marine hardware used for oil prospecting and extraction is now redundant and is being decommissioned. Over the next 20 years, it is estimated that some 4 400 structures will have to be removed worldwide. This presents an urgent need for technology that does not damage the seabed and avoids contamination from oil residues.

Band saw function

Conventional approaches used to cut through the legs of structures below the seabed – such as oxy-arc cutting or explosives – need significant amounts of material to be dredged away to gain access. Italian engineering SME Tecnospamec came up with the idea of using a hydraulically activated diamond wire cutter, operating in the manner of a band saw. Functions can be controlled and monitored from the surface or remotely operated vehicle (ROV).

"The sub bottom cutter is a pair of tubes, separated by about 5 ft (1.5 m), with drilling heads at the end. In between the pipes are placed pulleys on which runs the diamond wire cutting string," explains Eddie Grant, managing director of UK company Cutting Underwater Technologies.

"When the drilling heads at the end of the pipes bore into the seabed, suction within the pipes removes the debris into hoses, which deposit it into containers or onto the seabed some distance away. The diamond wire rotates on the pulleys and cuts right through the seabed with minimal disturbance. When it reaches the target material (i.e. the leg of the seabed structure), it goes right through that as well."

The technique was developed in an EU-funded project within the FP5 Growth Programme. Led by Tecnospamec as the design principal, the SBC project had participants from Greece, Italy, Norway and the UK. The Universities of Genoa and Athens were concerned with developing the robotics, and Monyana Engineering Services (UK) produced the drilling and suction dredging components. Hydrakraft in Norway developed suction anchors to hold the work platform in place on the seabed.

Cutting Underwater Technologies is responsible for marketing and operating the technology worldwide.

Recycling on a grand scale

More efficient and clean cutting is possible with the cutter, allowing complete re-use of the structures removed, avoiding the cost of scrapping and disposal. Apart from protecting the seabed and its flora and fauna from damage, the technique also minimises interference with the human activities of fisheries, seismic protection, cable trenching and underwater exploration, by not leaving pieces protruding from the seabed.

The project's environmental advantages match those of its engineering; recognised by a second place in the 2003 Award for Innovation & Excellence in SMEs from the UK Institution of Chemical Engineering.

Innovative aspects of the SBC technique that are already or in the process of being patented cover both the diamond wire cutter and the combined drilling/dredging system, together with the remotely operated, heavy-duty work platform. The drilling and dredging system cleans itself so that the dredged material does not interfere with the pulleys and the wire.

Eddie Grant explains the significance of these features. "Oil companies can in some cases apply for a dispensation from the Offshore Petroleum Activities Regulations so that they can cut subsea structures at or just below the mudline, and they can do this by conventional methods. Where there is no dispensation and they have to cut one to five metres below the seabed, they could cut from the inside of the structure with high pressure water abrasives, or they could use explosives.

"However, there is no guarantee that the structure is cut through, and also there is much damage to the seabed. So if the structure had to be cut below the seabed by conventional methods, dredging would be inevitable. Using the sub bottom cutter reduces the material moved by dredging from 1 000 or 1 500 to 10 or 15 cubic metres."

Developing a competitive edge

The project ran between March 2001 and June 2003. At the end of that time, SBC had a working prototype that was tested in sea trials off Norway, sponsored by four major oil companies: BP, Shell, Total Fina Elf and Amerada Hess.

"It's chicken-and-egg: to build one of our cutters costs about £2 million (€3 million), so as SMEs, we are not in a position to build them to leave on the shelf," says Eddie. "In the last two years we have marketed and exhibited all over the world, but we can't build until we are sure we have a customer. We hope that the oil companies which have backed our work so far are interested in using it."

Eddie believes that each partner has gained a competitive edge by participating in the project, and has also gained in prestige for developing such a strong environmental advance. The working prototype now available needs some refinements to build on the experience gained in the sea trials, particularly to increase the maximum width it could cut. A healthy market looks assured.

DG Research
http://europa.eu.int/comm/dgs/research/i ndex_en.html
Item source: http://europa.eu.int/comm/research/indus trial_technologies/articles/article_1169 _en.html