EAGE Glasgow 2000

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EAGE Glasgow 2000
Towards the Silent Seismic Source Reducing
Airborne Noise from Airguns
Mark Harper Mecon Limited, Cambridge, UK. Ian
Jack BP Amoco, Sunbury-on-Thames, UK Gerritt
Smeets Schlumberger, Gatwick Airport, UK
Mecon Ltd
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EAGE Glasgow 2000

• Why bother to reduce airgun noise?
• In environmentally sensitive areas, noise may
  disturb wildlife or residents
• 4D surveys can make things worse

Mecon Ltd
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EAGE Glasgow 2000
Proposed 4D survey in Poole Harbour, Dorset
(English South Coast)
Mecon Ltd
4
EAGE Glasgow 2000
Advantages and Disadvantages of the Airgun as a
Transition Zone Source

• High Energy Output in the Seismic Band
• Instantaneous Signal (convenient on a moving
  ship)..but..
• High Peak-Level Acoustic Noise

Mecon Ltd
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EAGE Glasgow 2000
How do Airguns Generate Acoustic Noise?
Possible Paths
1
4
Airgun Barge
3
2
Mecon Ltd
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EAGE Glasgow 2000
Field Measurements of Possible Paths GECO-Prakla
Gun Barge
Mecon Ltd
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EAGE Glasgow 2000
Field Measurements of Possible Paths Measurement
Positions Single Gun, 0.6L capacity
1
4
3
2
Airgun Barge
Hydrophone
Microphone
Accelerometer
Mecon Ltd
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EAGE Glasgow 2000
Measurements Near Gun
Pa
Pa
Microphone
Hydrophone
Sec
Sec
Mecon Ltd
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EAGE Glasgow 2000
Measurements On Barge
Pa
m/s2
Accelerometer
Microphone
Sec
Sec
Mecon Ltd
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EAGE Glasgow 2000
Measurements on Water 100m from Barge
Pa
Pa
Microphone
Hydrophone
Sec
Sec
Mecon Ltd
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EAGE Glasgow 2000
Measurements on Land 100m from Barge
Pa
m/s2
Accelerometer
Microphone
Sec
Sec
Mecon Ltd
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EAGE Glasgow 2000
Effect of Gun Depth Pressure on Acoustic Signal
at Various Distances
Mecon Ltd
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EAGE Glasgow 2000
Conclusions

• Acoustic signal from gun is not coupled to water
  wave or ground roll
• Propagation is omnidirectional (amplitude
  inversely proportional to distance)
• Sound is produced either by rigid-body scattering
  from the raft or by nonlinear effects near the
  gun

Mecon Ltd
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EAGE Glasgow 2000
Airgun Pop
Mecon Ltd
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EAGE Glasgow 2000
What now?

• A proof experiment is needed to decide whether
  noise is caused by scattering or by nonlinearity
• If by scattering, the cure is to stand the guns
  off from the barge
• If by nonlinearity, further investigation will be
  needed to decide the best method for noise
  reduction

Mecon Ltd