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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. 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


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


EAGE Glasgow 2000

Proposed 4D survey in Poole Harbour, Dorset (English South Coast)

Mecon Ltd


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


EAGE Glasgow 2000

How do Airguns Generate Acoustic Noise?

Possible Paths:

1

4

Airgun Barge

3

2

Mecon Ltd


EAGE Glasgow 2000

Field Measurements of Possible Paths:

GECO-Prakla Gun Barge

Mecon Ltd


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


EAGE Glasgow 2000

Measurements Near Gun

Pa

Pa

Microphone

Hydrophone

Sec

Sec

Mecon Ltd


EAGE Glasgow 2000

Measurements On Barge

Pa

m/s2

Accelerometer

Microphone

Sec

Sec

Mecon Ltd


EAGE Glasgow 2000

Measurements on Water 100m from Barge

Pa

Pa

Microphone

Hydrophone

Sec

Sec

Mecon Ltd


EAGE Glasgow 2000

Measurements on Land 100m from Barge

Pa

m/s2

Accelerometer

Microphone

Sec

Sec

Mecon Ltd


EAGE Glasgow 2000

Effect of Gun Depth & Pressure on Acoustic Signal at Various Distances

Mecon Ltd


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


EAGE Glasgow 2000

Airgun Pop

Mecon Ltd


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


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