Some notes on air-gun development as a marine seismic source

Ben F. Giles

doi:10.1190/1.3259610

Design of Near-orthogonal Air-gun Sequences for Marine Seismic Source Encoding

78th EAGE Conference and Exhibition 2016 ◽

10.3997/2214-4609.201600948 ◽

2016 ◽

Author(s):

M.B. Mueller ◽

D.F. Halliday ◽

D.J. van Manen ◽

J.O.A. Robertsson

Keyword(s):

Seismic Source ◽

Air Gun ◽

Marine Seismic ◽

Source Encoding

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Source signature encoding of a vertical source array to separate the emitted direct wave from its ghost

Geophysics ◽

10.1190/geo2017-0593.1 ◽

2018 ◽

Vol 83 (4) ◽

pp. P9-P18

Author(s):

Moritz B. Mueller ◽

David F. Halliday ◽

Dirk-Jan van Manen ◽

Johan O. A. Robertsson

Keyword(s):

Seismic Source ◽

Opposite Polarity ◽

Direct Wave ◽

Air Gun ◽

Short Period ◽

Separate Source ◽

Marine Seismic ◽

Separation Feature ◽

Marine Air ◽

Simultaneous Source

Marine air-gun sources can be sequence-encoded by firing their individual elements independently over a short period of time. Using near-orthogonal firing sequences, whose crosscorrelation is minimal, as encoding sequences for multiple sets of air-gun sources, enables us to exploit their orthogonality as a separation feature. We find that, by distributing air guns over depths from 5 to 30 m, firing sequences can be designed whose direct, down-going wavefield is close to orthogonal to its source-ghost wavefield. The fundamentally new aspect of this approach is that the source-ghost signal is no longer just a time-delayed, opposite-polarity version of the down-going wavefield, but due to the different air-gun depths results in a different source sequence. This enables the consideration of the ghost wavefield as a separate source. We generate a set of such firing sequences by minimizing the crosscorrelation of these wavefields and optimizing their respective autocorrelations to achieve sharp peaks. The obtained, optimized firing sequences are then used for marine seismic source encoding. By adapting a multifrequency algorithm originally developed for simultaneous source separation, we determine that the ghost-source wavefield can be separated as a separate source from the direct, down-going wavefield.

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Implementation of marine seismic source wavefields in finite-difference methods using wavefield injection

Geophysics ◽

10.1190/geo2016-0026.1 ◽

2016 ◽

Vol 81 (5) ◽

pp. T211-T219 ◽

Cited By ~ 2

Author(s):

Kjetil E. Haavik ◽

Espen Birger Raknes ◽

Martin Landrø

Keyword(s):

Finite Difference ◽

Finite Difference Methods ◽

Waveform Inversion ◽

Seismic Source ◽

Injection Technique ◽

Surface Reflection ◽

Air Gun ◽

True Source ◽

Grid Points ◽

Marine Seismic

We have developed a method for implementing source wavefields in finite-difference (FD) schemes for marine seismic modeling, migration, and inversion. By using the wavefield injection technique, it is possible to inject arbitrary source wavefields into an FD grid. We have assumed that the notional source signatures from each gun in an air-gun array and their positions are known. The source wavefield is extrapolated to a specified surface below the true source positions using analytical Green’s functions. On this surface, the pressure and its vertical derivative are inserted into the FD grid. The wavefield propagating from this surface will then propagate downward and appear as if it came from the true source position. The source positions do not need to coincide with the FD grid points, and the free-surface reflection coefficient for the source ghost can be specified; i.e., it can deviate from [Formula: see text], and it can be frequency dependent. These features are possible because of the analytical extrapolation step. The presented method allows modeling of any kind of marine seismic source as long as the notional source signature and radiation pattern from each individual source element is known. A simple full-waveform inversion example shows that it is important to honor the source geometry in forward modeling of seismic data.

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On low frequencies emitted by air guns at very shallow depths — An experimental study

Geophysics ◽

10.1190/geo2018-0687.1 ◽

2019 ◽

Vol 84 (5) ◽

pp. P61-P71 ◽

Cited By ~ 1

Author(s):

Daniel Wehner ◽

Martin Landrø ◽

Lasse Amundsen

Keyword(s):

Large Volume ◽

Field Experiments ◽

Field Measurements ◽

Seismic Source ◽

Sea Surface ◽

Frequency Signal ◽

Low Frequencies ◽

Air Gun ◽

Seismic Acquisition ◽

Marine Seismic

In marine seismic acquisition, the enhancement of frequency amplitudes below 5 Hz is of special interest because it improves imaging of the subsurface. The frequency content of the air gun, the most commonly used marine seismic source, is mainly controlled by its depth and the volume. Although the depth dependency on frequencies greater than 5 Hz has been thoroughly investigated, for frequencies less than 5 Hz it is less understood. However, recent results suggest that sources fired very close to the sea surface might enhance these very low frequencies. Therefore, we conduct dedicated tank experiments to investigate the changes of the source signal for very shallow sources in more detail. A small-volume air gun is fired at different distances from the water-air interface, including depths for which the air bubble bursts directly into the surrounding air. The variations of the oscillating bubble and surface disturbances, which can cause changes of the reflected signal from the sea surface, are explored to determine whether an increased frequency signal below 5 Hz can be achieved from very shallow air guns. The results are compared with field measurements of a large-volume air gun fired close to the sea surface. The results reveal an increased signal for frequencies below 5 Hz of up to 10 and 20 dB for the tank and field experiments, respectively, for the source depth at which the air gun bubble bursts directly into the surrounding air. For large-volume air guns, an increased low-frequency signal might also be achieved for sources that are slightly deeper than this bursting depth. From these observations, new design considerations in the geometry of air-gun arrays in marine seismic acquisition are suggested.

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Compact sleeve‐gun source arrays

Geophysics ◽

10.1190/1.1443058 ◽

1991 ◽

Vol 56 (3) ◽

pp. 402-407 ◽

Cited By ~ 5

Author(s):

P. M. Fontana ◽

T.‐A. Haugland

Keyword(s):

Small Volume ◽

Spectral Characteristics ◽

Seismic Source ◽

Pulse Amplitude ◽

Operational Efficiency ◽

Far Field ◽

Air Compressor ◽

Air Gun ◽

Marine Seismic

Data derived from far‐field signature measurements have inspired several guidelines for using clustered sleeve guns effectively in tuned marine seismic source arrays. Primarily, these data show that for a given volume the signature produced by a cluster of sleeve guns has a comparable bubble period, increased primary amplitude, and reduced bubble‐pulse amplitude compared to the signature of a single gun. These results agree with those reported for clusters of conventional air guns. However, when the data are analyzed in terms of acoustic and operational efficiency, we find that for array elements with volumes greater than [Formula: see text] two‐gun clusters are more desirable than equivalent volume clusters of several small volume guns. For array elements with volumes up to [Formula: see text], the data show no significant advantages for using clusters instead of single guns. These guidelines have led to the design of sleeve‐gun arrays that produce signatures with temporal and spectral characteristics equal to or exceeding those produced by conventional air‐gun arrays incorporating almost twice the total gun volume. Moreover, these new arrays operate with a total number of individual guns comparable to conventional arrays, thus improving the performance of source arrays on small survey vessels without having to increase air compressor capacity or ancillary source equipment.

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The shape of things to come — Development and testing of a new marine vibrator source

The Leading Edge ◽

10.1190/tle38090680.1 ◽

2019 ◽

Vol 38 (9) ◽

pp. 680-690 ◽

Cited By ~ 1

Author(s):

Benoît Teyssandier ◽

John J. Sallas

Keyword(s):

Seismic Source ◽

Test Facility ◽

Data Sets ◽

Far Field ◽

Ocean Bottom ◽

Air Gun ◽

Seismic Image ◽

Field Radiation ◽

Technical Issues ◽

To Come

Ten years ago, CGG launched a project to develop a new concept of marine vibrator (MV) technology. We present our work, concluding with the successful acquisition of a seismic image using an ocean-bottom-node 2D survey. The expectation for MV technology is that it could reduce ocean exposure to seismic source sound, enable new acquisition solutions, and improve seismic data quality. After consideration of our objectives in terms of imaging, productivity, acoustic efficiency, and operational risk, we developed two spectrally complementary prototypes to cover the seismic bandwidth. In practice, an array composed of several MV units is needed for images of comparable quality to those produced from air-gun data sets. Because coupling to the water is invariant, MV signals tend to be repeatable. Since far-field pressure is directly proportional to piston volumetric acceleration, the far-field radiation can be well controlled through accurate piston motion control. These features allow us to shape signals to match precisely a desired spectrum while observing equipment constraints. Over the last few years, an intensive validation process was conducted at our dedicated test facility. The MV units were exposed to 2000 hours of in-sea testing with only minor technical issues.

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Coherent noise in marine seismic data

Geophysics ◽

10.1190/1.1441516 ◽

1983 ◽

Vol 48 (7) ◽

pp. 854-886 ◽

Cited By ~ 65

Author(s):

Ken Larner ◽

Ron Chambers ◽

Mai Yang ◽

Walt Lynn ◽

Willon Wai

Keyword(s):

Seismic Data ◽

Noise Suppression ◽

Seismic Source ◽

Coherent Noise ◽

Critical Data ◽

Predictive Deconvolution ◽

Scattered Energy ◽

Marine Seismic ◽

The Many ◽

Water Bottom

Despite significant advances in marine streamer design, seismic data are often plagued by coherent noise having approximately linear moveout across stacked sections. With an understanding of the characteristics that distinguish such noise from signal, we can decide which noise‐suppression techniques to use and at what stages to apply them in acquisition and processing. Three general mechanisms that might produce such noise patterns on stacked sections are examined: direct and trapped waves that propagate outward from the seismic source, cable motion caused by the tugging action of the boat and tail buoy, and scattered energy from irregularities in the water bottom and sub‐bottom. Depending upon the mechanism, entirely different noise patterns can be observed on shot profiles and common‐midpoint (CMP) gathers; these patterns can be diagnostic of the dominant mechanism in a given set of data. Field data from Canada and Alaska suggest that the dominant noise is from waves scattered within the shallow sub‐buttom. This type of noise, while not obvious on the shot records, is actually enhanced by CMP stacking. Moreover, this noise is not confined to marine data; it can be as strong as surface wave noise on stacked land seismic data as well. Of the many processing tools available, moveout filtering is best for suppressing the noise while preserving signal. Since the scattered noise does not exhibit a linear moveout pattern on CMP‐sorted gathers, moveout filtering must be applied either to traces within shot records and common‐receiver gathers or to stacked traces. Our data example demonstrates that although it is more costly, moveout filtering of the unstacked data is particularly effective because it conditions the data for the critical data‐dependent processing steps of predictive deconvolution and velocity analysis.

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