Subsea Intervention & Survey

Electromagnetic Geoservices ASA (EMGS), specialists in Controlled-Source Electromagnetic Surveying (CSEM), is using 6G technologies from Sonardyne International Ltd. to provide redundancy and improved precision in EM source positioning. The technology will also be used to position and retrieve EM seabed receivers to the surface for data recovery.

Sonardyne 6G technology is used to position EMGS ASA’s EM source as it flies above seabed receivers. It is then used to relocate the receivers and issues a command to release them to the surface.

Pioneers of applying electromagnetic energy to oil and gas reservoir surveying, EMGS' method involves towing a long horizontal dipole behind a towfish flying about 30 meters above the seafloor. Seabed receivers already deployed measure the energy propagated through the sea and subsurface to measure the resistivity in the subsurface. CSEM relies on the difference in electrical resistivity between oil and water-bearing sediments; if the results show high resistivity, it's a good indication of the presence of hydrocarbons.

A Ranger 2 USBL system has been installed on the EM Leader survey vessel with DPT 6 mini transponders mounted on the EM source and the dipole at regular intervals along its length. The Ranger 2 system then tracks the position of the DPT 6s – and therefore, the EM source – as it flies above the seabed receivers. Once the data acquisition phase is complete, Ranger 2 is then used to relocate the seabed receivers (each fitted with its own acoustic transponder) and issues a command to release the receiver which then floats to the surface for recovery and data retrieval.

"We have considerable experience with Sonardyne technology, having used it for many years," commented Jonathan Fletcher, Supervisor Navigation Support at EMGS. "We wanted a system we could rely on to accurately and precisely position both the EM source and the seabed receivers and that could work alongside the other USBL system we also have onboard. Using Sonardyne 6G, we know that all our requirements will be fulfilled."

For more information about Ranger 2, click here.