Technology from Europe: United Kingdom
Reliable deepwater positioning reduces vessel time and acoustic interference
Industry’s move to deeper field development creates new demand for acoustic controls.
Gordon Johnston, Nautronix
Over the last 10 years Nautronix has been developing its ADS2 technology, and over the last five years it has developed NASNet. The company has a number of commercial projects using the system in the field and is developing the offshore subsea wireless controls market. Research and development began this year on the NASBOP and NASCoM acoustic control products. Investment has also been directed to the company’s support infrastructure.
The NASNet system is very similar in concept to GPS, as it permits unlimited users to obtain precise navigational data. However, unlike GPS, it provides this coverage at the sea surface and through the water column to the sea floor, regardless of working depth, Fig. 1. During November and December 2006, the company announced completion of a second deployment in the Mediterranean Sea. Reliable positioning, reduced vessel time and resistance to acoustic interference from other vessels give the system an advantage and save cost.
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Fig. 1. NASNet transmits and receives positioning data through the water column.
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The company won a three-year contract from the UK Ministry of Defence to supply a portable underwater acoustic range with a minimum of one deployment per year. The company manages the supply and installation of the range including vessel charter, ROV operations, fitting-out of receivers onboard multiple submarines, vessel manning, deploying and calibrating 31 NASNet stations in up to 1,500 m water depth, Fig. 2.
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Fig. 2. Thirty-one NASNet stations were deployed in up to 1,500-m water depths over 1,000 km2 in a recent trial.
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During this latest trial, the company covered 1,000 km2 with an acoustic array, enabling subsurface and surface positioning of multiple vessels. The company believes this is the first time an acoustic array of this size has ever been deployed. During the trial, the customer used data and text telemetry to communicate between submarines and surface vessels at more than a 20-mi separation.
The system also was deployed successfully in deep West African waters using NASNet Mini Stations. During the deployment, changing circumstances risked delays. To prevent this, the company used contingency backup components—construction receivers—to position the ROVs. The company successfully deployed the system within the specified time with no downtime. The company has a number of projects in Brazil and West Africa, including a 14-unit, sled-based system being deployed in West Africa later this year.
Looking forward, the company sees opportunities for development of underwater wireless controls for the offshore industry and is working with a number of projects to develop this capability. This comes on the back of Shell’s adoption, use and continuing investment in NASBOP technology. This technology is for the acoustic control and monitoring of subsea isolation devices for surface BOP drilling.
The next generation of subsea acoustic wireless control and monitoring systems, NASCoM, is now being developed for broader applicability. The work will extend the existing control capabilities while retaining the proven ADS2 signalling technology.
This technology will be used on an ultra-deepwater, semisubmersible drilling rig being built by Keppel FELS Ltd for Ensco International Inc. The vessel will use dual NASDrill RS925 multi-hydrophone, long baseline/short baseline, acoustic positioning systems. The recent drilling industry upturn has also renewed interest in and purchase of the company’s pig tracking and diver communications equipment.
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