Attenuated high-frequency emission from a new design of air-gun

Coste, E; Gerez, David; Groenaas, Halvor; Larsen, Ola Pramm; Wolfstirn, Michel; Hopperstad, Jon-Fredrik; Laws, Robert; Norton, Jack; Padula, Matthew

doi:10.1190/segam2014-0445.1

Cited by 27 publications

(15 citation statements)

References 16 publications

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“…New types of air guns have been recently designed in order to decrease the acoustic output at non‐relevant frequencies without compromising the pulse shape within the seismic frequency range (Coste et al . ). A greater benefit would result from the deployment of marine seismic vibrators in place of impulsive sources.…”

Section: Benefits Of Dispersed Source Array Acquisitionsmentioning

confidence: 97%

“…Note that higher frequencies considerably contribute to the total emitted energy, which is often the main parameter taken into consideration by regulators. New types of air guns have been recently designed in order to decrease the acoustic output at non-relevant frequencies without compromising the pulse shape within the seismic frequency range (Coste et al 2014). A greater benefit would result from the deployment of marine seismic vibrators in place of impulsive sources.…”

Section: Marine Environmental Issuesmentioning

confidence: 99%

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Broadband imaging via direct inversion of blended dispersed source array data

Caporal

Blacquière

Davydenko

2018

Geophysical Prospecting

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Although seismic sources typically consist of identical broadband units alone, no physical constraint dictates the use of only one kind of device. We propose an acquisition method that involves the simultaneous exploitation of multiple types of sources during seismic surveys. It is suggested to replace (or support) traditional broadband sources with several devices individually transmitting diverse and reduced frequency bands and covering together the entire temporal and spatial bandwidth of interest. Together, these devices represent a so‐called dispersed source array. As a consequence, the use of simpler sources becomes a practical proposition for seismic acquisition. In fact, the devices dedicated to the generation of the higher frequencies may be smaller and less powerful than the conventional sources, providing the acquisition system with increased operational flexibility and decreasing its environmental impact. Offshore, we can think of more manageable boats carrying air guns of different volumes or marine vibrators generating sweeps with different frequency ranges. On land, vibrator trucks of different sizes, specifically designed for the emission of particular frequency bands, are preferred. From a manufacturing point of view, such source units guarantee a more efficient acoustic energy transmission than today's complex broadband alternatives, relaxing the low‐ versus high‐frequency compromise. Furthermore, specific attention can be addressed to choose shot densities that are optimum for different devices according to their emitted bandwidth. In fact, since the sampling requirements depend on the maximum transmitted frequencies, the appropriate number of sources dedicated to the lower frequencies is relatively small, provided the signal‐to‐noise ratio requirements are met. Additionally, the method allows to rethink the way to address the ghost problem in marine seismic acquisition, permitting to tow different sources at different depths based on the devices' individual central frequencies. As a consequence, the destructive interference of the ghost notches, including the one at 0 Hz, is largely mitigated. Furthermore, blended acquisition (also known as simultaneous source acquisition) is part of the dispersed source array concept, improving the operational flexibility, cost efficiency, and signal‐to‐noise ratio. Based on theoretical considerations and numerical data examples, the advantages of this approach and its feasibility are demonstrated.

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Section: Benefits Of Dispersed Source Array Acquisitionsmentioning

confidence: 97%

Section: Marine Environmental Issuesmentioning

confidence: 99%

Broadband imaging via direct inversion of blended dispersed source array data

Caporal

Blacquière

Davydenko

2018

Geophysical Prospecting

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“…The low frequencies (below ∼100 Hz) are geophysically useful; they coherently penetrate the subsurface and reflect from targets of interest. The higher frequencies, however, are attenuated faster, scattered more by heterogeneous overburden, unable to penetrate as deep (Ziolkowski et al, 2003) and are of limited benefit to imaging (Coste et al, 2014). Furthermore, in conventional seismic acquisition receivers typically sample at 2 ms meaning that any signal above the Nyquist frequency of 250 Hz is not recovered.…”

Section: Introductionmentioning

confidence: 99%

What controls the initial peak of an air-gun source signature?

2019

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Seismic air guns are broadband sources that generate acoustic waves at many frequencies. The low frequency waves can be used for imaging while the high frequency waves are attenuated and/or scattered before they can reflect from targets of interest in the subsurface. It is desirable to reduce the amplitude of the high frequency acoustic waves as they are thought to be disruptive, and potentially damaging, to marine life and are not useful for geophysical purposes. The high frequency acoustic waves are primarily associated with the initial expansion of the air gun bubble and associated peak in the acoustic pressure time series, which is commonly referred to as the source signature of the air gun. Here, we develop a quasi-one-dimensional model of a seismic air gun coupled to a spherical bubble that accounts for gas dynamics and spatially variable depressurization inside the firing chamber in order to investigate controls on the initial peak of the source signature. The model is validated against data collected during field tests in Lake Seneca, New York. Simulations and field data both show that the initial peak is primarily dependent on the operating pressure. A lower gun pressure results in a smaller peak amplitude and a slower rise time. The slope, the amplitude of the initial peak divided by the rise time, is used as a proxy for environmental impact and can decrease by as much as 50% when the air gun pressure is reduced from 2000 psi to 1000 psi. The low frequencies are controlled by the total discharged mass, which is dependent upon gun volume and pressure. Decreasing the operating pressure while simultaneously increasing the gun volume will reduce the high frequencies while maintaining the desirable low frequency signals.

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“…Coste et al (2014) present a new design of air guns that reduces amplitudes at high frequencies to mitigate the effect on marine mammals. In addition, major research efforts are carried out on marine vibrators.…”

Section: Introductionmentioning

confidence: 99%

Low-frequency acoustic signal created by rising air-gun bubble

Wehner

Landrø

2017

GEOPHYSICS

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In the seismic industry, there is increasing interest in generating and recording low frequencies, which leads to better data quality and can be important for full-waveform inversion. The air gun is a seismic source with a signal that consists of the (1) main impulse, (2) oscillating bubble, and (3) rising of this air bubble. However, there has been little investigation of the third characteristic. We have studied a low-frequency signal that could be created by the rising air bubble and find the contribution to the low-frequency content in seismic acquisition. We use a simple theory and modeling of rising spheres in water and compute the acoustic signal created by this effect. We conduct tank and field experiments with a submerged buoy that is released from different depths and record the acoustic signal with hydrophones along the rising path. The experiments simulate the signal from the rising bubble separated from the other two effects (1 and 2). Furthermore, we use data recorded below a single air gun fired at different depths to investigate if we can observe the proposed signal. We find that the rising bubble creates a low-frequency signal. Compared with the main impulse and the oscillating bubble effect of an air-gun signal, the contribution of the rising bubble is weak, on the order of 1/900 depending on the bubble size. By using large air-gun arrays tuned to create one big bubble, the contribution of the signal can be increased. The enhanced signal can be important for deep targets or basin exploration because the low-frequency signal is less attenuated.

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Attenuated high-frequency emission from a new design of air-gun

Cited by 27 publications

References 16 publications

Broadband imaging via direct inversion of blended dispersed source array data

Broadband imaging via direct inversion of blended dispersed source array data

What controls the initial peak of an air-gun source signature?

Low-frequency acoustic signal created by rising air-gun bubble

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