Western Onshore Basin, ONGC, Vadodara,

Email: anjankrbakshi@yahoo.co.in

10th Biennial International Conference & Exposition

P 407

Effective Surface wave attenuation in cross spread domain

– A case study from Cambay Basin

Anjan K. Bakshi*, Puneet Saxena

Summary

Surface wave noise generally obscure seismic signal during recording of data by single point sensor in land seismic reflection

exploration. Key problem is how to effectively attenuate surface waves and remnant surface waves during the noise attenuation

in processing. This work demonstrates a technique of attenuating surface waves in the three dimensions frequency-

wavenumber domain on cross spread based on a grid of modified Inline and Crossline without altering the actual shots and

receivers positions. Here the new grid we call it as pseudo grid. The method is applied to the raw 3D shot gather of seismic

data acquired in the Western Onshore Basin, Vadodara. For the remnant surface wave mute guided multichannel spectrum

editing technique is applied. Finally, comparing the time slices and gathers before and after using the strategy, it is observed

that the method, described here, attenuates surface waves and remnant surface waves effectively and improves the signal to

noise ratio without weakening the desired reflected signal.

Keywords: Cambay Basin, Surface Wave Attenuation

Introduction

Strategy of noise attenuation with respect to signal depends

upon the fact how the characteristics of noise differs from

signal in terms of a particular physical quantity in a

specific domain This work deals with surface noise

attenuation in cross-spread domain.

Due to several reasons it may not be possible to take shots

with regular orthogonal geometry (fig.1a). In such

situation layout of a particular cross-spread with respect to

a receiver line is not be an ideal cross

(fig.1b).Effectiveness of 3D Fk filter to attenuate the

Figure 1: Cross-Spread layout. a) All cross-spreads along a

receiver line 911. b) Single cross-spread along the same receiver

line with respect to shot line 1651.

surface noise seems to be not reaching to its optimum level.

On time slice surface waves appear as concentric circles

but due to irregular shot disposition it does not remain so

(fig.2a). In the pseudo grid of modified Inline and crossline

numbers corresponding to regular orthogonal geometry it

becomes concentric (fig.2b) 3D FK Filter becomes

Figure 2: Cross-Spread Time Slices at 646 ms. a) Actual grid. b)

Pseudo grid.

effective in the pseudo grid. As the positions of source and

receivers are not changed therefore, in subsequent stages

of processing integrity of data is maintained

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Theory

The data acquired with orthogonal geometry can be

considered as a collection of cross-spreads (Vermeer,

2002). Each intersection of a source line and a receiver line

forms the center of a cross-spread. The dense sampling of

the sources along the source line and of the receivers along

the receiver line creates a dense single-fold areal coverage.

The midpoints of traces with the same absolute offset are

located on a circle with diameter equal to that offset.

Therefore, the first arrivals of the ground roll are lying on

the surface of a circular cone. Hence, the ground roll in a

cross-spread behaves as a truly three-dimensional event

and can best be removed by a 3D FK filter. Karagül et al.

(2004) demonstrated that this 3D filter performs

considerably better than the cascaded application of two

2D FK filters. But due to irregular shot locations those

circles are not perfect circles. In order to make them perfect

for optimum performance of 3D FK filter, a new grid was

created that had its X-axis along the inline direction and its

Y-axis along the crossline direction. In that new system

sources were binned using their X-coordinates so as to

obtain new source line header that would have a number

falling on the ideal source line by calculating the deviation

of shots from its ideal shotline in terms of no. of crossline

depending upon the binning of geometry and then by

making correction in crossline. The similar procedure can

be applied in case of irregularity in receiver position.

However, in the present study correction is applied to the

crosslines only as the receiver lines are almost straight.

Procedure

Surface wave attenuation procedure was carried out on a

3D seismic volume which was taken from Western

Onshore Basin. Time slices of shot gather in both actual as

well as in pseudo grid has been shown in fig.3.

Figure 3: Cross-Spread Time Slices at 3600 ms. a) in original

grid. b) in pseudo grid.

The slices show that the circles are more regular in pseudo

grid. Application of 3D FK filter was showing better result

when applied in new grid system in comparison to that

applied in original grid (fig.4). It is obvious that the surface

Figure 4: Application of 3D FK filter. a) in original grid. b) in

pseudo grid.

noise was not fully attenuated in both the grid system but

time slice in pseudo grid is comparatively less noisy. When

above time slices were compared with the input dataset, it

reveals the effectiveness of psudo grid(fig.5). All the data

set were shown in the same grid that is in the original grid

so that one can have the idea how much surface noise was

attenuated when the data was brought back into the original

grid. In order to attenuate remnant surface noise, frequency

dependent multi channel spectral editing was carried out in

original grid. Application was restricted to the surface

wave noise zone only by using an internal mute. Noise

band was kept below 14 Hz. Time slices in fig.6 shows the

comparison of remnant surface noise attenuation in both

Figure 5: Comparision of 3D FK Filtering. a) Input. b) in original

grid. c) in pseudo grid

Figure 6: Comparision of residual surface noise attenuation. a)

Input. b) 3D FK filtering c) 3D FK filtering and frequency

dependent multichannel editing.

the grids and then those were compared with the input data

set. Further, to validate the result a comparative study was

carried out in shot gather mode also (fig.7).

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Figure 7: Comparision of 3D FK filtering in Shot gather mode.

a) Input. b) in original grid c) in pseudo grid

Figure 8: Comparision of data set after surface noise

attenuation. a) Input. b) 3D FK filtering c) 3D FK filtering and

frequency dependent multi channel editing.

Input data in shot gather mode was also compared with the

data set after applying 3D FK filter followed by frequency

dependent multichannel editing (fig.8). Care was taken in

designing of filter so that no signal is lost. That has been

shown in fig.9 by taking differences between input and the

filtered data sets. The display gain of the difference section

(fig.9b) was slightly increased in comparison to ensure that

no signal should lost.

Figure 9: a) Input data set. b) difference with denoised data set

Conclusions

Surface wave attenuation in cross spread domain after

reorientation in pseudo grid can lead to better imaging of

final output in case of data acquired with orthogonal

geometry. Quality is further increased by applying mute

guided frequency dependent multi channel editing in

cascade with 3D FK filtering.

Acknowledgements

The authors are thankful to ONGC for providing

infrastructure to carry out this work. The authors are

thankful to Shri S.K.Das, ED-Basin Manager, WON Basin

Baroda for permission to publish this work. Thanks are due

to Shri U.S.D. Pandey, GGM ,Head Geophysical services,

Vadodara for his keen interest and providing support for

acquisition of the multicomponent data. The authors are

thankful to Shri G. Sarvesam, Ex ED-OSD, Project

Coordinator, 3D-3C and Shri B K Barve, GM (GP), 3D-

3C for their initiatives and valuable suggestions during the

project. Authors are also thankful to Shri M K Jain,

DGM(S) and Shri S S Singh, DGM(S) for the critical

analysis during study.

Last but not the least, thanks to all the members of 3D-3C

project who were directly or indirectly involved in the

analysis of the data.

References

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is missing? 3DSymSam – Geophysical Advice,

Oldemarkt, The Netherlands

Karagül, A., Crawford, R., Sinden, J., and Ali, S.,

2003,Recent advances in 3D land processing: Examples

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Liao Jianping, Wang Huazhong, Li Weibo, Ma Zaitian. 3D

Partial Differential Equation Filtering and Linear Noise

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Mustafa Al-Ali and Gerrit Blacquière.

Velocityindependent determination of 3D focusing

operators using cross-spreads. Expanded Abstracts of

75th SEG Mtg, 2005,1830~1834

Vermeer, G., O., J. [2008] Alternative strategies for

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WU Hua, LI Yan-feng, Ren Chao-fa, Removing Surface

Wave by Cross-Spread Technology and Application.

Exploration and Development Research Institute of

Daqing Oilfield Company Ltd., Daqing City,163712,

China

The views expressed in the paper are solely of the authors

and do not necessarily reflect the views of the organization

which they belong to.