“A Seismic Shift Towards Quieter Surveys”

Editor’s note: Marine Technology posted the above-titled article by Elaine Maslin.  The article reads as follows:

“Since the earliest days of offshore oil and gas exploration, the need to “shoot” seismic surveys has been helping companies to find the hydrocarbons they can then produce.

Seismic data helps geophysicists and geologists understand the rock formations in the earth, what might be happening in them and, crucially, if they might contain oil and gas. Similar to acquiring seismic data onshore, it means emitting sound energy (a source) then detecting its return and interpreting that information to image the subsurface.

While the industry moved away from use of dynamite as a source in the 1960s, the sound energy created, now mostly by air guns, can still impact marine life. As such, it’s use is highly regulated. Many countries use UK-based Joint Nature Conservation Committee guidance, which will see activity delayed if a marine mammal is detected within 500m. The Australian National Offshore Petroleum Safety and Environmental Management Authority has a 1-3km zone, while in Brazil and Ireland it’s 1km. There are also other bodies with their own guidance as well as country specific regulations. Most mean having onboard mammal observers and towed passive acoustic monitoring (with PAM onboard unmanned vessels also emerging). Some countries have even banned seismic exploration altogether (Italy has had a temporary ban in place pending new assessments).

But, there’s still pressure to protect marine life so there’s also work to rethink the source. Since 2011, a group comprising of Total, Shell and ExxonMobil has been working on alternatives, based on marine vibroseis technology, under a joint industry project managed by Texas A&M University. Marine vibroseis works by emitting a continuous lower level energy. “Instead of a clap, one instantaneous instance of noise with high peak to peak pressure ratio, we propose a quiet hum in the background, but is designed to have the same seismic energy as the clap,” says Andrew Feltham, Research Geophysicist – Acquisition, at Total. “We’re substituting high amplitude with a longer duration. The idea is to have a quieter instantaneous peak to peak pressure level and significantly reduce, if not eliminate, potential harm to the marine environment.”

The marine industry has been trying to use this technology this since the 1960s, by taking land vibroseis technologies offshore, but with “with limited success”. Because of this, the JIP was formed, contracting with three different companies. Some haven’t worked, but one has, says Feltham; Applied Physical Sciences (APS), part of General Dynamics, which has developed the Marine Vibrator – Integrated Projector Node (MV-IPN).”

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