ROV industry getting down to the challenge of deepwater

Published March 27th, 2001 - 02:00 GMT

Now that the price of oil has reached what passes for normality, a new surge of innovation seems to be gripping the ROV (Remotely Operated Vehicle) industry.  

 

Lessons learned from the days of the US$10 bbl have been absorbed by ROV manufacturers who are now looking at ways of providing a more competitive service.  

 

The industry’s move into deep water has also prompted some notable examples of lateral thinking from ROV manufacturers recently.  

 

Because anything below 300 meters lies beyond the reach of divers the prospect of working at 2,500 meters places an even greater emphasis on the capabilities of the ROV and the very major costs involved.  

 

While the oil industry was in the doldrums, the most profitable ROV business was picked-up from the submarine cable-laying business which is still going through an Internet feeding frenzy.  

 

Needing ROVs for survey, installation, and maintenance tasks, the industry has stimulated a respectable level of innovation aimed at meeting the need to bury cables beneath the seabed in deeper waters.  

 

With the fishing industry also moving into deep water, the risk of cable damage from trawls now exists at depths previously considered safe. It is, however, more difficult for conventional cable ploughs to perform well in deep water due to the energy needed to pull both the plough and its heavy tow line.  

 

Being self-propelled, ROVs can largely overcome this problem. Using water jets that blast trenches to considerable depths, manufacturers have been investing in innovation and new product development.  

 

SMD has, for example, recently introduced its powerful new Marcas III “superclass” ROV. Rated to 2,500 meters, the vehicle is capable of cable burial up to three meters deep and is unique in that it uses SMD’s new TrencheROV balancing capability.  

 

This is a patented system that moves the position of the ROV’s thrusters and buoyancy to compensate for the counter-thrust created by the jetting tool and is said to need up to 50% less power than a conventional ROV.  

 

Presumably with less happening on the oil side of its business, Sonsub had the resources and motivation to develop the Centaur.  

 

This is a hybrid consisting of a massive tracked skid equipped with a water jet trenching tool. For the skid to function, an Innovator work class ROV docks with it on the seabed to provide the power and control needed to operate it as a self-propelled seabed tractor.  

 

This is considered more efficient than having much of the available power used by the ROV’s thrusters rather than the jetting tool.  

 

Sonsub claims the system provides the additional benefit of keeping an ROV available for conventional deployment by itself if needed.  

 

It recently occurred to Oceaneering that much is to be said for having a ROV handy – particularly if the working unit needs back-up. Oceaneering consequently launched the Hydra Minimum ROV system last year.  

 

This mini electric-powered observation-class vehicle was developed for use in conjunction with the Hydra Magnum work-class vehicle.  

 

Measuring just 14-inches high and 60-inches long, it is operated from its own cage Tether Management System (TMS) which is attached to the bottom of a standard Magnum TMS cage.  

 

It has a 1,000-ft TMS umbilical that gives it the freedom to investigate any problem with the Magnum or provide additional flexibility for tasks requiring the presence of two ROVs.  

 

Electric vs hydraulic thrusters:  

Despite these innovations in ROV design, the question of electric versus hydraulic thrusters persists as a major topic of debate.  

 

The question becomes more acute as manufacturers gear their products for deepwater operations where conventional ROV umbilicals – perhaps 50mm in diameter - can be a big liability. When coiled on a winch, two km of such umbilical creates a formidable load demanding a big and expensive support vessel.  

 

Hydraulic-powered ROVs are now starting to look a lot less attractive for use in deep water when compared with the latest electric work-class vehicles.  

 

A new generation of brushless DC electric motors has made them very reliable, and they also use a much thinner umbilical – typically just 27 or 28 mm, providing a dramatic reduction in the cable-handling requirements on the support vessel with corresponding cost savings. 

 

Oceaneering has long acknowledged that the fundamental requirement of all ROV operations is to be able to keep the vehicle in the water for as long as possible and this means that vehicle reliability must be given priority.  

 

Oceaneering’s ambitions have been helped dramatically through a comprehensive operator training program that has reportedly reduced vehicle downtime to just .3 percent.  

 

The relative simplicity of electric propulsion compared with hydraulic thrusters is also likely to boost reliability, and Oceaneering has recently introduced an all-electric version of its Magnum work-class ROV.  

 

Several ROV manufacturers are offering electric vehicles including Sub-Atlantic, Argus Remote Systems, Shark Marine, and Hydro-vision. The British company Hydro-Lek also makes hydraulic tool skids so that electric-powered observation-class vehicles can be given working capability.  

 

The most talked-about innovation can, however, be found on the Alstom Schilling Robotics Quest ROV, which entered service with Canyon Offshore last year. The vehicle weighs an anorexic 1,700 kg and is powered by seven unique 7.5 kW electric ring thrusters.  

 

The electric ring motors are hardly bigger than the propellers themselves and combine compactness with low weight and reliability—said to enable the Quest to deliver the performance of a 150 hp hydraulic vehicle while being smaller, faster, lighter, and simpler to maintain.  

 

While electric ROVs bring the benefit of lower cost support vessels, the use of Autonomous Underwater Vehicles (AUVs) for seafloor surveys combine higher quality data with even greater savings.  

 

ROVs make slow and expensive survey vehicles, whereas AUVs dispense with umbilicals entirely and have a launch-and-forget capability that means they can be deployed from an even smaller vessel of opportunity.  

 

Equipped with a suite of survey sensors, they can follow a pre-programmed route and download their stored data on return. If necessary, several AUVs can be launched from the same boat to study different areas simultaneously and achieve previously unimaginable survey productivity. 

 

There are now some five or six contenders with AUVs available on the market or under development. Competition is getting fierce with C&C Technologies, for example, leading the field in the US Gulf of Mexico, where it has taken delivery of a Hugin AUV from Kongsberg Simrad.  

 

Maridan of Denmark has also conducted five commercial surveys with its own AUVs and recently sold one to De Beers Marine for diamond field surveys.  

 

Thales GeoSolutions (formerly Racal Survey) is also close behind and is expected to be offering survey services using the two Sea Oracle AUVs it has on order from Bluefin Robotics.  

 

Equipped with side scan sonar, sub-bottom profiler, and swathe bathymetry, the Sea Oracle will be able to work for up to 20 hours and in sea conditions that would make ROV operation impractical.  

 

The lack of real time communications means that so far nobody is talking about a work-class AUV. Nevertheless, Cybernetix of France is coming close with its Swimmer, which consists of a shuttle AUV that carries its own work-class ROV.  

 

The shuttle is launched from a platform, FPSO, or a vessel of opportunity from which it flies on battery power, guided by auto pilot and acoustic positioning, to a seabed installation. This may be in very deep water and a considerable distance away from the launch site.  

 

The destination could be a wellhead, manifold, or seabed processing module such as the acclaimed Alpha PRIME system for which the concept is particularly suitable.  

 

The shuttle automatically docks with the structure and connects to a power supply and communications linkage that, in the case of the AlphaPRIME, would already be present as an integral part of its design.  

 

Once docked, real-time control is assumed by a surface pilot,who is able to launch the ROV from the shuttle to which it remains connected by a conventional umbilical.  

 

The ROV is able to undertake a normal range of work tasks around the installation and remain on the seabed indefinitely, allowing the support vessel to depart.  

 

At the end of the mission, the ROV returns to the shuttle which, with its batteries fully recharged, unlocks from the seabed module and returns automatically to the surface.  

The first demonstration of the Swimmer is scheduled for April.  

 

If successful, the concept is likely to be seized by the offshore industry as the first practical escape from the tyranny of the umbilical.  

 

It will also become the first ROV system to be designed into the structure of a seabed installation and will mark a step change in the way the industry works with and thinks about one of its most important tools. 

By Paul Eastaugh, Berkshire, UK  

(oilandgasonline)  

© 2001 Mena Report (www.menareport.com)

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