Offshore seismic surveys
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Offshore seismic surveys
Why do we conduct seismic surveys?
Marine seismic surveys are a part of the first steps in oil and gas exploration, and a very important one since the images of the subsurface generated are used to identify possible oil and gas accumulations.
Seismic surveys are being used in practically all oil and gas exploration projects worldwide. Both on- and offshore.
Since the 1950s, dozens of seismic surveys have been carried out offshore Argentina.
How do they work?
A seismic survey is a type of geophysical exploration technique that produces images of the rocks beneath the surface of the Earth.
For marine surveys purpose-built vessels with specialized equipment are used. The seismic vessel travels at low speed, less than 5 knots, and tow a series of cables called streamers behind the vessel. The streamers contain sensors that capture seismic data from the subsurface. The streamer array can span up to two kilometres in width and ten kilometres in length.
To collect seismic data short bursts of compressed air are released from a sound source into the water towards the seafloor, every five to fifteen seconds. This creates low frequency sound waves that pass through the water, the sea floor and into the subsurface layers. Then the sound waves are reflected up to the sea surface where they are recorded by the sensors.
When the sound has been sent from the sound source, the sound level rapidly decreases. The accumulated time of sound output constitutes less than 5 percent of the total survey time.
Back on land the data acquired during the survey are processed and interpreted by geoscientists to identify areas where oil and gas may be present.
Safe seismic surveys
In Equinor we always make sure that international standards and best safety practices are applied to our seismic operations. We spend several months of careful planning to ensure operations are conducted safely and efficiently, with minimal impact to the environment and other marine activities in the area.
For safety reasons support vessels are used during operations to warn other marine users that a survey is taking place.
During our seismic operations offshore Argentina, we will have dedicated mammal observers onboard the seismic vessel to monitor and record marine life, such as whales, turtles and dolphins. Their task is to ensure that animals sensitive to low frequency sounds are not nearby prior to starting the sound source. Once the sound source is started, the sound output is increased slowly to give animals time to move away.
If animals are observed nearby during the seismic acquisition, the sound output will be paused until they are well outside the exclusion zone (1,000 metres) defined by the Argentinian authorities.
Equinor has conducted hundreds of surveys safely and successfully all over the world since the company was founded in 1972. Being one of the world’s largest offshore operators, safety is our number one priority, for both people and the environment.