Variable source depth acquisition for improved marine broadband seismic data

Haavik, Kjetil Eik; Landrø, Martin

doi:10.1190/geo2014-0437.1

Cited by 17 publications

(4 citation statements)

References 23 publications

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“…The source depth might be limited by practical issues when towing sources that shallow. An investigation on the source ghost effect for different source depths is demonstrated by Haavik & Landrø (2015), however the shallowest source depths in this study is 3 m. Due to high noise levels at these frequencies caused by ocean swell, 4C ocean-bottom receivers are preferable to recognize this effect as they have a better signal-to-noise ratio at these low frequencies Halliday et al 2015). For the modelled results from experiment B, the same deghosting method as for experiment A is performed which leads to a big change of the estimated ratio (Fig.…”

Section: Discussionmentioning

confidence: 99%

Frequency-depth-dependent spherical reflection response from the sea surface — a transmission experiment

Wehner¹,

Landrø²,

Amundsen

et al. 2018

Geophysical Journal International

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In academia and the industry, there is an increasing interest in generating and recording low seismic frequencies, which lead to better data quality, deeper signal penetration and can be important for full-waveform inversion. The common marine seismic source in acquisition is the air gun which is towed behind a vessel. The frequency content of the signal produced by the air gun mainly depends on its source depth as there are two effects that are presumed to counteract each other. First, there is the oscillating air bubble generated by the air gun that leads to more low frequencies for shallow source depths. Second, there is the interference of the downgoing wave with the first reflection from the sea surface, referred to as the ghost, which leads to more low frequencies for deeper source depths. It is still under debate whether it is beneficial to place the source shallow or deep to generate the strongest signal for frequencies below 5 Hz. Therefore, the ghost effect is studied in more detail by measuring the transmission at the water-air interface. We conduct experiments in a water tank where a small-volume seismic source is fired at different depths below the water surface to investigate how the ghost varies with frequency and depth. The signal from the seismic source is recorded with hydrophones inside water and air during the test to estimate the transmitted signal through the interface. In a second test, we perform experiments with an acoustic source located in air that is fired at different elevations above the water surface. The source in air is a starter gun and the signals are again recorded in water and air. The measured data indicate an increasing transmission of the signal through the water-air interface when the source is closer to the water surface which leads to a decreasing reflection for sources close to the surface. The measured results are compared with modelled data and the existing theory. The observed increase in transmission for shallow source depths could be explained by the theory of a spherical wave front striking the interface instead of assuming a plane wave front. The difference can be important for frequencies below 1 Hz. The results suggest that deploying a few sources very shallow during marine seismic acquisition could be beneficial for these very low frequencies. In addition, the effect of a spherical wave front might be considered for modelling far-field signatures of seismic sources for frequencies below 1 Hz.

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Section: Discussionmentioning

confidence: 99%

Frequency-depth-dependent spherical reflection response from the sea surface — a transmission experiment

Wehner¹,

Landrø²,

Amundsen

et al. 2018

Geophysical Journal International

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“…Firing source arrays at different depths with a time delay to create a constructive downgoing wavefield is beneficial for low frequencies (Cambois et al, 2009). Shooting the air guns at variable depths is another approach to improve the frequency content of the signal (Haavik and Landrø, 2015). These methods are still under investigation, and the more complicated the shooting pattern, the more demanding is the processing of the data.…”

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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“…So their solutions may become unstable or non-unique. Although there has been enormous development in seismic acquisition technology to achieve the acquisition of broadband seismic signals (Day et al 2013;Kroode et al 2013;Haavik and Landrø 2015), the signal-to-noise ratio (SNR) of low-and high-frequency components is also controversial topics, specifically for frequencies lower than 2-5 Hz and higher than 100 Hz. However, low frequencies play an important role in seismic exploration, especially for resolution enhancement, better imaging quality, effective inversion processes and direct fluid identification.…”

Section: Introductionmentioning

confidence: 99%

Bayesian seismic multi-scale inversion in complex Laplace mixed domains

Yin

Zong

2017

Pet. Sci.

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Seismic inversion performed in the time or frequency domain cannot always recover the long-wavelength background of subsurface parameters due to the lack of low-frequency seismic records. Since the low-frequency response becomes much richer in the Laplace mixed domains, one novel Bayesian impedance inversion approach in the complex Laplace mixed domains is established in this study to solve the model dependency problem. The derivation of a Laplace mixed-domain formula of the Robinson convolution is the first step in our work. With this formula, the Laplace seismic spectrum, the wavelet spectrum and time-domain reflectivity are joined together. Next, to improve inversion stability, the object inversion function accompanied by the initial constraint of the linear increment model is launched under a Bayesian framework. The likelihood function and prior probability distribution can be combined together by Bayesian formula to calculate the posterior probability distribution of subsurface parameters. By achieving the optimal solution corresponding to maximum posterior probability distribution, the low-frequency background of subsurface parameters can be obtained successfully. Then, with the regularization constraint of estimated low frequency in the Laplace mixed domains, multi-scale Bayesian inversion in the pure frequency domain is exploited to obtain the absolute model parameters. The effectiveness, anti-noise capability and lateral continuity of Laplace mixed-domain inversion are illustrated by synthetic tests. Furthermore, one field case in the east of China is discussed carefully with different input frequency components and different inversion algorithms. This provides adequate proof to illustrate the reliability improvement in low-frequency estimation and resolution enhancement of subsurface parameters, in comparison with conventional Bayesian inversion in the frequency domain.

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Variable source depth acquisition for improved marine broadband seismic data

Cited by 17 publications

References 23 publications

Frequency-depth-dependent spherical reflection response from the sea surface — a transmission experiment

Frequency-depth-dependent spherical reflection response from the sea surface — a transmission experiment

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

Bayesian seismic multi-scale inversion in complex Laplace mixed domains

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