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Montevideo, February 21st 2019 - 05:49 UTC
Environmentalists in New Zealand asked the government to halt an offshore oil exploration project being conducted for Brazilian oil giant Petrobras in the wake of the deaths of dozens of penguins, the press reported. Read full article
oil exploration in the sea and its consecuences www.diariopanorama.com/seccion/firmas_22/catastrofe-ecologica-en-malvinas-a-causa-de-la-explotacion-petrolera_a_89345
The Petrobras seismic surveys are, almost certainly, one or two air-gun arrays towed about 200 m behind the survey vessel, with cables, called streamers, containing a few thousand hydrophone sensors
Air-gun arrays typically involve 12-48 individual guns and an air-gun releases a volume of air under high pressure, creating a sound pressure wave.
The acoustic pressure output of an air-gun array is directly proportional to its operating pressure, 2,000psi, and the peak pressure levels emitted from commonly used seismic industry air-gun arrays are in the 5-300 Hz range.
Vertical output is maximized - while minimizing output in the
horizontal plane - through the use of focused arrays incorporating more small airguns rather than one or a few larger air-guns.
The maximum pressure level an animal could experience from an air-gun source in use today in the seismic industry will be 240 dB, vertically under the vessel array. Sound/pressure levels are minimal horizontally away from the array – ie, away from the vessel where penguins might be.
During a survey run, the array is towed at 5 knots and is fired every 10 seconds. A typical seismic operation involves a series of parallel passes by a vessel towing one or two air-gun arrays.
Thus, a seismic crew can get into and out of a specific area much more quickly than in times past because fewer tracks are required, given the wider coverage (swath) of the attenuated return signal per track.
When an oil field is up and running they sometimes use seismic time-lapse monitoring (4D) for reservoir management (repeating seismic surveys to monitor changes in a hydrocarbon reservoir and draw-down over the months and years of its productive life). This means that is more seismic activity over *producing* fields than was true in the past.
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