SEISMIC SIGNATURES OF LARGE AIR GUNS

Geophysics ◽  
1971 ◽  
Vol 36 (6) ◽  
pp. 1162-1173 ◽  
Author(s):  
W. Harry Mayne ◽  
Roy G. Quay
Keyword(s):  
Energy Levels ◽  
Low Frequency ◽  
Experimental Tests ◽  
Frequency Spectra ◽  
Seismic Surveys ◽  
Air Gun ◽  
Absolute Energy ◽  
Overall Performance ◽  
Marine Seismic ◽  
Effective Source

Large chamber air guns are a reliable and effective source of energy for marine seismic surveys. Air guns with chamber volumes of 300 and 1000 cubic inches demonstrate desirable low‐frequency responses and high absolute energy levels. Overall performance has been compromised, however, by the bubble effect. Previous attempts at minimizing the bubble response have resulted in loss of reliability, reduced power, or incomplete bubble suppression, or a combination thereof. In this paper, we present the results of experimental tests on air guns with 300 and 1000 cubic inch chambers and describe a divided‐chamber gun which greatly attenuates the bubble effect. Significant improvements in the width and flatness of the frequency spectra are demonstrated by analysis of the actual signatures obtained in deep water and with record sections comparing the results obtained with the standard and improved guns along an identical traverse. The bubble‐attenuating air gun simultaneously provides improved resolution, high absolute‐energy levels, and excellent reliability.

scholarly journals Deep learning for low-frequency extrapolation from multioffset seismic data

Geophysics ◽  
2019 ◽  
Vol 84 (6) ◽  
pp. R989-R1001 ◽  
Author(s):  
Oleg Ovcharenko ◽  
Vladimir Kazei ◽  
Mahesh Kalita ◽  
Daniel Peter ◽  
Tariq Alkhalifah
Keyword(s):  
Deep Learning ◽  
Seismic Data ◽  
Signal To Noise Ratio ◽  
Waveform Inversion ◽  
Low Frequency ◽  
Low Frequencies ◽  
Seismic Surveys ◽  
Full Waveform ◽  
Frequency Components ◽  
Marine Seismic

Low-frequency seismic data are crucial for convergence of full-waveform inversion (FWI) to reliable subsurface properties. However, it is challenging to acquire field data with an appropriate signal-to-noise ratio in the low-frequency part of the spectrum. We have extrapolated low-frequency data from the respective higher frequency components of the seismic wavefield by using deep learning. Through wavenumber analysis, we find that extrapolation per shot gather has broader applicability than per-trace extrapolation. We numerically simulate marine seismic surveys for random subsurface models and train a deep convolutional neural network to derive a mapping between high and low frequencies. The trained network is then tested on sections from the BP and SEAM Phase I benchmark models. Our results indicate that we are able to recover 0.25 Hz data from the 2 to 4.5 Hz frequencies. We also determine that the extrapolated data are accurate enough for FWI application.

scholarly journals Streamer depth versus vessel and seismic interference noise

Geophysics ◽  
2017 ◽  
Vol 82 (4) ◽  
pp. P41-P51
Author(s):  
Toan Dao ◽  
Martin Landrø
Keyword(s):  
Noise Level ◽  
Cutoff Frequency ◽  
Normal Modes ◽  
Low Frequency ◽  
Data Set ◽  
The North ◽  
Interference Noise ◽  
Air Gun ◽  
Seismic Surveying ◽  
Marine Seismic

For marine seismic surveying, it is commonly assumed that the noise level decreases with depth. In addition, recent advances in broadband seismic have shown that a greater receiver depth is beneficial in preserving low-frequency data. However, in a heavily trafficked ocean, noise from other ships, including seismic interference, is a counteractive process in which the noise actually varies with depth. Normal modes can be used to explain and predict the ship noise and seismic interference noise level. We find that weather noise is dominant below the first mode’s cutoff frequency (approximately 6 Hz), ship noise is dominant from that frequency to the upper end of the useful seismic frequency band (80 Hz). We have used a data set in which the streamer was towed at 8, 45, and 60 m depths in three passes over the same area in the North Sea. The water depth is 135 m on average. We observe that the noise level at 45 and 60 m depth is approximately 1.6 times stronger than that at 8 m. We find that the air-gun energy is up to 46 dB stronger than the noise from the seismic vessel. However, the total noise from all the ships within several hundred kilometers radius can reduce the data quality.

scholarly journals Airgun blasts used in marine seismic surveys have limited effects on mortality, and no sublethal effects on behaviour or gene expression, in the copepod Calanus finmarchicus

2019 ◽  
Vol 76 (7) ◽  
pp. 2033-2044 ◽  
Author(s):  
David M Fields ◽  
Nils Olav Handegard ◽  
John Dalen ◽  
Christiane Eichner ◽  
Ketil Malde ◽  
...  
Keyword(s):  
Escape Response ◽  
Field Experiments ◽  
Sublethal Effects ◽  
Low Frequency ◽  
Calanus Finmarchicus ◽  
Sensory Threshold ◽  
Seismic Surveys ◽  
Commercially Important ◽  
Or Gene ◽  
Marine Seismic

Abstract Seismic surveys use airguns that emit low frequency high magnitude sound to detect subsea resources and to map seabed geology. The effect of seismic blasts on Calanus spp., a key food source for commercially important fish, was assessed in field experiments. Immediate mortality of copepods was significantly different from controls at distances of 5 m or less from the airguns. Mortality 1 week after the airgun blast was significantly higher—by 9% relative to controls—in the copepods placed 10 m from the airgun blast but was not significantly different from the controls at a distance of 20 m from the airgun blast. The increase in mortality—relative to controls—did not exceed 30% at any distance from the airgun blast. Only two genes changed in response to the airgun blast; however, their function is unknown. There were no sublethal effects of the seismic blasts on the escape performance or the sensory threshold needed to initiate an escape response at any of the distances from the airgun blast that were tested. Results from these experiments suggest that seismic blasts have limited effects on the mortality or escape response of Calanus sp. within 10 m of the blast and no measurable impact at greater distances.

Low-frequency spectra and change of state

1960 ◽  
Vol 255 (1280) ◽  
pp. 78-80
Keyword(s):  
Gas Phase ◽  
High Pressures ◽  
Energy Levels ◽  
Frictional Coefficient ◽  
Low Frequency ◽  
Ultra Violet ◽  
Rotational Relaxation ◽  
Frequency Spectra ◽  
Change Of State ◽  
Van Vleck

The majority of contributions to the Discussion have been concerned with the ultra-violet and infra-red spectral regions, but important considerations also arise at lower frequencies. These have been less fully studied because of experimental difficulties, but experiments show that changes in the spectrum consequent on* change of state may be quite large. In the gas phase, rotational energy levels are usually described in quantum- mechanical language in terms of the angular momentum. In the liquid phase the equivalent levels are not quantized and the motion can be treated on classical lines in terms of a frictional coefficient and a rotational relaxation time. Formally the Debye (1929) dielectric loss formula may be derived (Whiffen 1950 a ) as a special case of the Van Vleck & Weisskopf (1945) gas phase formula by allowing the transition frequencies all to tend to zero and the line width parameter, Δ v , to become 1/2πr. Measurements at high pressures, especially above the critical temperature, would be expected to show the properties of an intermediate case.

Delaying the source ghost to improve the ultralow-frequency response of a marine air-gun source

Geophysics ◽  
2020 ◽  
Vol 85 (5) ◽  
pp. P45-P51
Author(s):  
Honglei Shen ◽  
Thomas Elboth ◽  
Chunhui Tao ◽  
Gang Tian ◽  
Hanchuang Wang ◽  
...  
Keyword(s):  
Seismic Data ◽  
Waveform Inversion ◽  
Low Frequency ◽  
Ultralow Frequency ◽  
Full Waveform ◽  
Air Gun ◽  
Marine Source ◽  
Frequency Output ◽  
Marine Seismic ◽  
Marine Air

The competing effect between the fundamental bubble and its source-ghost response results in a strong attenuation of the lowest frequencies (below 7 Hz). This loss cannot be compensated easily by adjusting the source depth. Consequently, the low-frequency content in marine seismic data is not optimal, degrading the performance of low-frequency dependent processing approaches, such as full-waveform inversion. To overcome this, we have developed an additional source to counteract the ghost from the main source. In this situation, the fundamental bubble is characterized by the depth of the main source, whereas the ghost response is characterized by the summed depth of the main and additional sources. This source setup mitigates the competing effect and reduces the suppression of ultralow frequencies. Compared with a conventional horizontal source, our source design will reduce the mid- to high-frequency output, which may be beneficial in situations in which environmental constraints limit the maximum allowed output of a marine source.

The music of marine seismic: A marine vibrator system based on folded surfaces

2020 ◽  
Vol 39 (4) ◽  
pp. 254-263
Author(s):  
Okwudili C. Orji ◽  
Mattias Oscarsson-Nagel ◽  
Walter Söllner ◽  
Endrias G. Asgedom ◽  
Øystein Trætten ◽  
...  
Keyword(s):  
Seismic Data ◽  
Frequency Tuning ◽  
Synthetic Data ◽  
Harmonic Distortion ◽  
Low Frequency ◽  
Source Control ◽  
Environmental Friendliness ◽  
Air Gun ◽  
Frequency Module ◽  
Marine Seismic

Marine vibrators have bespoke geophysical benefits that are yet to be harnessed because of robustness and efficiency issues. We have developed a new marine vibrator source technology that is efficient and stable. The source technology overcomes the historical problems of inefficiency and robustness by using folded surface technology and resonance frequency tuning. We show measured output examples that demonstrate that the folded surface concept combined with small displacements can provide the required output levels. Our source system consists of a low-frequency module covering 1–10 Hz and a high-frequency module covering 10–125 Hz. The source control system has shown high stability and precision and can handle harmonic distortion. With the aid of synthetic data examples, we demonstrate that seismic data acquired using marine vibrators in either intermittent or continuous mode can be processed. Finally, we demonstrate the environmental friendliness of the source in comparison to air gun-based sources.

scholarly journals Exposure to seismic air gun signals causes physiological harm and alters behavior in the scallop Pecten fumatus

2017 ◽  
Vol 114 (40) ◽  
pp. E8537-E8546 ◽  
Author(s):  
Ryan D. Day ◽  
Robert D. McCauley ◽  
Quinn P. Fitzgibbon ◽  
Klaas Hartmann ◽  
Jayson M. Semmens
Keyword(s):  
Blood Cell ◽  
Sublethal Effects ◽  
Low Frequency ◽  
Repeated Exposure ◽  
Seismic Signals ◽  
Seismic Surveys ◽  
Naturally Occurring ◽  
Air Gun ◽  
Behavioral Parameters ◽  
The Impact

Seismic surveys map the seabed using intense, low-frequency sound signals that penetrate kilometers into the Earth’s crust. Little is known regarding how invertebrates, including economically and ecologically important bivalves, are affected by exposure to seismic signals. In a series of field-based experiments, we investigate the impact of exposure to seismic surveys on scallops, using measurements of physiological and behavioral parameters to determine whether exposure may cause mass mortality or result in other sublethal effects. Exposure to seismic signals was found to significantly increase mortality, particularly over a chronic (months postexposure) time scale, though not beyond naturally occurring rates of mortality. Exposure did not elicit energetically expensive behaviors, but scallops showed significant changes in behavioral patterns during exposure, through a reduction in classic behaviors and demonstration of a nonclassic “flinch” response to air gun signals. Furthermore, scallops showed persistent alterations in recessing reflex behavior following exposure, with the rate of recessing increasing with repeated exposure. Hemolymph (blood analog) physiology showed a compromised capacity for homeostasis and potential immunodeficiency, as a range of hemolymph biochemistry parameters were altered and the density of circulating hemocytes (blood cell analog) was significantly reduced, with effects observed over acute (hours to days) and chronic (months) scales. The size of the air gun had no effect, but repeated exposure intensified responses. We postulate that the observed impacts resulted from high seabed ground accelerations driven by the air gun signal. Given the scope of physiological disruption, we conclude that seismic exposure can harm scallops.

“Single bubble” air‐gun array for deep exploration

Geophysics ◽  
1993 ◽  
Vol 58 (3) ◽  
pp. 366-382 ◽  
Author(s):  
F. Avedik ◽  
V. Renard ◽  
J. P. Allenou ◽  
B. Morvan
Keyword(s):  
Energy Content ◽  
Low Frequency ◽  
Pulse Generation ◽  
Acoustic Energy ◽  
Petroleum Exploration ◽  
Single Bubble ◽  
Seismic Exploration ◽  
Deep Penetration ◽  
Air Gun ◽  
Marine Seismic

Large tuned air‐gun arrays operated in off‐shore petroleum exploration are also used for deep penetration marine seismic reflection surveys conducted to define structures in the earth’s crust. Because of the attenuation of higher frequencies, the useful upper frequency limit of these records is usually about 50–60 Hz. The aim of this paper is to report on a method of seismic pulse generation that preferentially concentrates the air gun’s energy in the low range of the seismic frequency band by centering the output on the first “bubble pulse” instead of the initial (primary) pulse. Experimental results show that, due to the increased low‐frequency energy content of this “single bubble” pulse, air‐gun arrays considerably reduced both in size and volume can generate the necessary acoustic energy for deep seismic exploration.

Shot repetition: An alternative seismic blending code in marine acquisition

Geophysics ◽  
2018 ◽  
Vol 83 (6) ◽  
pp. P29-P37 ◽  
Author(s):  
Sixue Wu ◽  
Gerrit Blacquière ◽  
Gert-Jan Adriaan van Groenestijn
Keyword(s):  
Source Code ◽  
Seismic Exploration ◽  
Data Quality Control ◽  
Time Data ◽  
Alternative Source ◽  
Seismic Surveys ◽  
Air Gun ◽  
Seismic Acquisition ◽  
Marine Seismic ◽  
Source Encoding

In blended seismic acquisition, or simultaneous source seismic acquisition, source encoding is essential at the acquisition stage to allow for separation of the blended sources at the processing stage. In land seismic surveys, the vibroseis sources may be encoded with near-orthogonal sweeps for blending. In marine seismic surveys, the sweep type of source encoding is difficult because the main source type in marine seismic exploration is the air-gun array, which has an impulsive character. Another issue in marine streamer seismic data acquisition is that the spatial source sampling is generally coarse. This hinders the deblending performance of algorithms based on the random time delay blending code that inherently requires a dense source sampling because they exploit the signal coherency in the common-receiver domain. We have developed an alternative source code called shot repetition that exploits the impulsive character of the marine seismic source in blending. This source code consists of repeated spikes of ones and can be realized physically by activating a broadband impulsive source more than once at (nearly) the same location. Optimization of the shot-repetition type of blending code was done to improve the deblending performance. As a result of using shot repetition, the deblending process can be carried out in individual shot gathers. Therefore, our method has no need for a regular dense source sampling: It can cope with irregular sparse source sampling; it can help with real-time data quality control. In addition, the use of shot repetition is beneficial for reducing the background noise in the deblended data. We determine the feasibility of our method on numerical examples.

Identification of and Favorable Conditions for a New Long-Offset Seismic Phase from Offshore–Onshore Seismic Surveys

2021 ◽  
Author(s):  
Changrong Zhang ◽  
Shaohong Xia ◽  
Jinghe Cao ◽  
Kuiyuan Wan ◽  
Cheng Xiong
Keyword(s):  
Seismic Waves ◽  
River Estuary ◽  
Low Frequency ◽  
Seismic Survey ◽  
Apparent Velocity ◽  
Seismic Surveys ◽  
Practical Applications ◽  
Air Gun ◽  
Crustal Structures ◽  
Favorable Conditions

Abstract Offshore–onshore seismic survey is one of the main methods to study crustal structures in offshore–onshore transitional zones. At present, the seismic waves commonly used in imaging are the crustal refraction (Pg), the crustal reflection from the Moho (PmP), and the upper-mantle refraction (Pn) waves. The propagation distances of Pg and PmP are commonly less than 210 km, and Pn propagates with an apparent velocity of ∼8  km/s. In 2015, two offshore–onshore wide-angle seismic lines with a length of ∼350  km were acquired in the Pearl River Estuary. In addition to Pg, PmP, and Pn, a new seismic phase was observed, which has a long propagation distance (offset of ∼170–290  km), low apparent velocity (∼5.85  km/s), and low frequency (∼4–7  Hz). Similar seismic phases have been widely reported in previous offshore–onshore and reservoir seismic surveys, but the understanding of these phases is still limited. Herein, we used both raytracing and waveform modeling methods to identify the new seismic phase as the secondary Pg phase, which reflects from the surface (named Pg2Pg). We also discuss favorable conditions for Pg2Pg, including (1) a thin sedimentary layer with low velocity at the surface in which the reflection of Pg occurs, which can reduce the incidence angles and hence increase the energy of the reflected waves; (2) a sedimentary basement dipping toward the sea at the positions of the air gun shots, which focuses seismic waves; (3) relatively smooth interfaces of the medium, which can reduce the scattering of Pg2Pg; and (4) air guns that can excite low-frequency signals, which can reduce the attenuation of seismic waves. Checkerboard tests and practical applications show that Pg2Pg can significantly improve upper-crustal resolution, especially for onshore areas. Our research promotes the data mining of offshore–onshore seismic surveys, which is important for obtaining more detailed crustal structures.

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