Improving the Low-frequency Content of Borehole Seismic Data Acquired Using an Air-gun Source

The lack of the low-frequency information in field data prohibits the time- or frequency-domain waveform inversions from recovering large-scale background velocity models. On the other hand, Laplace-domain waveform inversion is less sensitive to the lack of the low frequencies than conventional inversions. In theory, frequency filtering of the seismic signal in the time domain is equivalent to a constant multiplication of the wavefield in the Laplace domain. Because the constant can be retrieved using the source estimation process, the frequency content of the seismic data does not affect the gradient direction of the Laplace-domain waveform inversion. We obtained inversion results of the frequency-filtered field data acquired in the Gulf of Mexico and two synthetic data sets obtained using a first-derivative Gaussian source wavelet and a single-frequency causal sine function. They demonstrated that Laplace-domain inversion yielded consistent results regardless of the frequency content within the seismic data.

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Broadband seismic over/under sources and their designature-deghosting

Geophysics ◽

10.1190/geo2016-0512.1 ◽

2017 ◽

Vol 82 (5) ◽

pp. P61-P73 ◽

Cited By ~ 3

Author(s):

Lasse Amundsen ◽

Ørjan Pedersen ◽

Are Osen ◽

Johan O. A. Robertsson ◽

Martin Landrø

Keyword(s):

Seismic Data ◽

High Frequency ◽

Low Frequency ◽

Point Sources ◽

High Frequency Side ◽

Frequency Content ◽

Source Depth ◽

Deep Sources ◽

The Cost ◽

High Frequency Content

The source depth influences the frequency band of seismic data. Due to the source ghost effect, it is advantageous to deploy sources deep to enhance the low-frequency content of seismic data. But, for a given source volume, the bubble period decreases with the source depth, thereby degrading the low-frequency content. At the same time, deep sources reduce the seismic bandwidth. Deploying sources at shallower depths has the opposite effects. A shallow source provides improved high-frequency content at the cost of degraded low-frequency content due to the ghosting effect, whereas the bubble period increases with a lesser source depth, thereby slightly improving the low-frequency content. A solution to the challenge of extending the bandwidth on the low- and high-frequency side is to deploy over/under sources, in which sources are towed at two depths. We have developed a mathematical ghost model for over/under point sources fired in sequential and simultaneous modes, and we have found an inverse model, which on common receiver gathers can jointly perform designature and deghosting of the over/under source measurements. We relate the model for simultaneous mode shooting to recent work on general multidepth level array sources, with previous known solutions. Two numerical examples related to over/under sequential shooting develop the main principles and the viability of the method.

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Accuracy of wavelets, seismic inversion, and thin-bed resolution

Interpretation ◽

10.1190/int-2017-0023.1 ◽

2017 ◽

Vol 5 (4) ◽

pp. T523-T530

Author(s):

Ehsan Zabihi Naeini ◽

Mark Sams

Keyword(s):

Seismic Data ◽

Reservoir Characterization ◽

Low Frequency ◽

Seismic Inversion ◽

Inversion Method ◽

Frequency Content ◽

Frequency Model ◽

North West ◽

The North ◽

Well Data

Broadband reprocessed seismic data from the North West Shelf of Australia were inverted using wavelets estimated with a conventional approach. The inversion method applied was a facies-based inversion, in which the low-frequency model is a product of the inversion process itself, constrained by facies-dependent input trends, the resultant facies distribution, and the match to the seismic. The results identified the presence of a gas reservoir that had recently been confirmed through drilling. The reservoir is thin, with up to 15 ms of maximum thickness. The bandwidth of the seismic data is approximately 5–70 Hz, and the well data used to extract the wavelet used in the inversion are only 400 ms long. As such, there was little control on the lowest frequencies of the wavelet. Different wavelets were subsequently estimated using a variety of new techniques that attempt to address the limitations of short well-log segments and low-frequency seismic. The revised inversion showed greater gas-sand continuity and an extension of the reservoir at one flank. Noise-free synthetic examples indicate that thin-bed delineation can depend on the accuracy of the low-frequency content of the wavelets used for inversion. Underestimation of the low-frequency contents can result in missing thin beds, whereas underestimation of high frequencies can introduce false thin beds. Therefore, it is very important to correctly capture the full frequency content of the seismic data in terms of the amplitude and phase spectra of the estimated wavelets, which subsequently leads to a more accurate thin-bed reservoir characterization through inversion.

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The Wolfspar experience with low-frequency seismic source field data: Motivation, processing, and implications

The Leading Edge ◽

10.1190/tle41010010.1 ◽

2022 ◽

Vol 41 (1) ◽

pp. 9-18

Author(s):

Andrew Brenders ◽

Joe Dellinger ◽

Imtiaz Ahmed ◽

Esteban Díaz ◽

Mariana Gherasim ◽

...

Keyword(s):

Gulf Of Mexico ◽

Seismic Data ◽

Field Data ◽

Model Building ◽

Low Frequency ◽

Seismic Source ◽

Velocity Model ◽

Seismic Sources ◽

Velocity Model Building ◽

Air Gun

The promise of fully automatic full-waveform inversion (FWI) — a (seismic) data-driven velocity model building process — has proven elusive in complex geologic settings, with impactful examples using field data unavailable until recently. In 2015, success with FWI at the Atlantis Field in the U.S. Gulf of Mexico demonstrated that semiautomatic velocity model building is possible, but it also raised the question of what more might be possible if seismic data tailor-made for FWI were available (e.g., with increased source-receiver offsets and bespoke low-frequency seismic sources). Motivated by the initial value case for FWI in settings such as the Gulf of Mexico, beginning in 2007 and continuing into 2021 BP designed, built, and field tested Wolfspar, an ultralow-frequency seismic source designed to produce seismic data tailor-made for FWI. A 3D field trial of Wolfspar was conducted over the Mad Dog Field in the Gulf of Mexico in 2017–2018. Low-frequency source (LFS) data were shot on a sparse grid (280 m inline, 2 to 4 km crossline) and recorded into ocean-bottom nodes simultaneously with air gun sources shooting on a conventional dense grid (50 m inline, 50 m crossline). Using the LFS data with FWI to improve the velocity model for imaging produced only incremental uplift in the subsalt image of the reservoir, albeit with image improvements at depths greater than 25,000 ft (approximately 7620 m). To better understand this, reprocessing and further analyses were conducted. We found that (1) the LFS achieved its design signal-to-noise ratio (S/N) goals over its frequency range; (2) the wave-extrapolation and imaging operators built into FWI and migration are very effective at suppressing low-frequency noise, so that densely sampled air gun data with a low S/N can still produce useable model updates with low frequencies; and (3) data density becomes less important at wider offsets. These results may have significant implications for future acquisition designs with low-frequency seismic sources going forward.

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Multi‐Level airgun array: A simple and effective way to enhance the low frequency content of marine seismic data

10.1190/1.3255140 ◽

2009 ◽

Cited By ~ 6

Author(s):

Guillaume Cambois ◽

Andrew Long ◽

Gregg Parkes ◽

Terje Lundsten ◽

Anders Mattsson ◽

...

Keyword(s):

Seismic Data ◽

Low Frequency ◽

Frequency Content ◽

Multi Level ◽

Marine Seismic

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Borehole seismic‐source radiation pattern in transversely isotropic media

Geophysics ◽

10.1190/1.1443759 ◽

1995 ◽

Vol 60 (1) ◽

pp. 29-42 ◽

Cited By ~ 7

Author(s):

Wenjie Dong ◽

M. Nafi Toksöz

Keyword(s):

Radiation Effects ◽

Low Frequency ◽

Transversely Isotropic ◽

Seismic Source ◽

Wave Pattern ◽

Radiation Patterns ◽

S Wave ◽

Source Radiation ◽

Air Gun ◽

Borehole Seismic

We extend previous discussions on crosswell tomography in anisotropic formations by deriving the radiation patterns of three typical downhole seismic sources (impulsive air gun or dynamite, wall‐clamped vertical vibrators, and cylindrical bender) inside a fluid‐filled borehole embedded in a transversely isotropic (TI) formation. The method of steepest descents, in conjuncture with the low‐frequency and far‐field assumptions, is applied to the exact displacement integrals of these sources to obtain their radiation patterns asymptotically. In spite of complications caused by quasi‐P‐ and quasi‐SV‐wave coupling and wavefront triplication in homogeneous TI media, the final results can still be expressed in slowness components determined by a ray direction, which is desired when source radiation effects are to be accounted for by ray‐based tomography techniques. Tests with the radiation patterns show that while the effect of anisotropy on P‐waves is moderate, its effect on the S‐wave pattern is significant even for slightly anisotropic formations. One can predict the S‐wave pattern from the sign of the Thomsen’s measure δ*.

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

Geophysics ◽

10.1190/geo2019-0680.1 ◽

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.

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

The Leading Edge ◽

10.1190/tle39040254.1 ◽

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.

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Combining Wireline and LWD Borehole Seismic Data for Drilling HPHT Well: A Novel Approach

10.2523/13083-ms ◽

2009 ◽

Author(s):

Teck Kean Lim ◽

Aqil Ahmed ◽

Muhammad Antonia Gibrata ◽

Gunawan Taslim

Keyword(s):

Seismic Data ◽

Novel Approach ◽

Borehole Seismic

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APPLICATION OF THE EMPIRICAL MODE DECOMPOSITION METHOD TO GROUND-ROLL NOISE ATTENUATION IN SEISMIC DATA

Brazilian Journal of Geophysics ◽

10.22564/rbgf.v31i4.342 ◽

2013 ◽

Vol 31 (4) ◽

pp. 619 ◽

Cited By ~ 1

Author(s):

Luiz Eduardo Soares Ferreira ◽

Milton José Porsani ◽

Michelângelo G. Da Silva ◽

Giovani Lopes Vasconcelos

Keyword(s):

Empirical Mode Decomposition ◽

Seismic Data ◽

Low Frequency ◽

High Amplitude ◽

Seismic Line ◽

Seismic Processing ◽

Mode Decomposition ◽

Ground Roll ◽

Fortran 90 ◽

Emd Method

ABSTRACT. Seismic processing aims to provide an adequate image of the subsurface geology. During seismic processing, the filtering of signals considered noise is of utmost importance. Among these signals is the surface rolling noise, better known as ground-roll. Ground-roll occurs mainly in land seismic data, masking reflections, and this roll has the following main features: high amplitude, low frequency and low speed. The attenuation of this noise is generally performed through so-called conventional methods using 1-D or 2-D frequency filters in the fk domain. This study uses the empirical mode decomposition (EMD) method for ground-roll attenuation. The EMD method was implemented in the programming language FORTRAN 90 and applied in the time and frequency domains. The application of this method to the processing of land seismic line 204-RL-247 in Tacutu Basin resulted in stacked seismic sections that were of similar or sometimes better quality compared with those obtained using the fk and high-pass filtering methods.Keywords: seismic processing, empirical mode decomposition, seismic data filtering, ground-roll. RESUMO. O processamento sísmico tem como principal objetivo fornecer uma imagem adequada da geologia da subsuperfície. Nas etapas do processamento sísmico a filtragem de sinais considerados como ruídos é de fundamental importância. Dentre esses ruídos encontramos o ruído de rolamento superficial, mais conhecido como ground-roll . O ground-roll ocorre principalmente em dados sísmicos terrestres, mascarando as reflexões e possui como principais características: alta amplitude, baixa frequência e baixa velocidade. A atenuação desse ruído é geralmente realizada através de métodos de filtragem ditos convencionais, que utilizam filtros de frequência 1D ou filtro 2D no domínio fk. Este trabalho utiliza o método de Decomposição em Modos Empíricos (DME) para a atenuação do ground-roll. O método DME foi implementado em linguagem de programação FORTRAN 90, e foi aplicado no domínio do tempo e da frequência. Sua aplicação no processamento da linha sísmica terrestre 204-RL-247 da Bacia do Tacutu gerou como resultados, seções sísmicas empilhadas de qualidade semelhante e por vezes melhor, quando comparadas as obtidas com os métodos de filtragem fk e passa-alta.Palavras-chave: processamento sísmico, decomposição em modos empíricos, filtragem dados sísmicos, atenuação do ground-roll.

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