Approximating subsurface structure in areas of severe subsea erosion—A nonprocessing technique

Geophysics ◽  
1989 ◽  
Vol 54 (11) ◽  
pp. 1397-1409
Author(s):  
Fred W. Lishman ◽  
Michael N. Christos
Keyword(s):  
Seismic Data ◽  
Seismic Reflection ◽  
Velocity Model ◽  
Subsurface Structure ◽  
Submarine Canyons ◽  
Arrival Times ◽  
Sea Floor ◽  
Static Corrections ◽  
Map Migration ◽  
Made In

Severe subsea erosion distorts seismic reflection times and velocity analyses and makes determining subsurface structure difficult. Although data reprocessing is the logical solution for removing these distortions, reprocessing can be expensive. We present a case history describing a nonprocessing depth‐conversion technique using a geologic erosional model. A grid of common‐midpoint seismic data located in and around several submarine canyons was used for this study. Establishing a geologic erosional model requires an accurate representation of the sea floor, which we obtain by map migration of the sea‐floor reflection. A velocity model was developed using only those analyses not adversely affected by sea‐floor erosion. To remove the effects of erosion from the arrival times of a mapped horizon, static corrections (velocity replacement and compaction) were developed. We replaced the water velocity in the eroded section with depth‐equivalent rock velocities from the velocity model. The compaction correction, which was derived empirically, is based on the assumption that porosity restoration occurred in the sediments beneath the canyons when erosion reduced the overlying pressure. Compaction correction in conjunction with velocity replacement produced structure maps (time and depth) that exhibit only minor effects of erosion. These results were further improved by applying dynamic corrections obtained by ray tracing a subsurface model to determine the traveltime through the water for the reflection from the mapped horizon. Our final structure maps demonstrate that a geologically reasonable structural interpretation in depth can be made in areas of severe subsea erosion without reprocessing the data.

On: “Approximating subsurface structure in areas of severe subsea erosion — A nonprocessing technique” by F. W. Lishman, and M. N. Christos (GEOPHYSICS, 54, 1397–1409, November 1989).

Geophysics ◽  
1990 ◽  
Vol 55 (11) ◽  
pp. 1512-1513
Author(s):  
C. J. Blyth
Keyword(s):  
Data Processing ◽  
Seismic Data ◽  
Seismic Velocities ◽  
Subsurface Structure ◽  
Reasonable Accuracy ◽  
Processing Methods ◽  
Sea Floor ◽  
Accurate Model ◽  
Mapping Structures ◽  
Data Processing Methods

Two important questions were addressed in this paper. Firstly, how to construct an accurate model of a sea floor canyon — its topography and associated seismic velocities. Secondly, how the effects of such canyons can be accounted for in obtaining depths to subcanyon reflections using conventionally processed seismic data. An answer to the first question is required not only for deriving depths from conventional data but is equally required of the various canyon‐solving data processing methods listed in the paper (p. 1397). The second question is important, as the authors say, to provide a quick and inexpensive reconnaissance method of mapping structures in depth with reasonable accuracy.

Deep‐water peg legs and multiples: Emulation and suppression

Geophysics ◽  
1986 ◽  
Vol 51 (12) ◽  
pp. 2177-2184 ◽  
Author(s):  
J. R. Berryhill ◽  
Y. C. Kim
Keyword(s):  
Wave Equation ◽  
Seismic Data ◽  
Water Layer ◽  
Original Data ◽  
Equation Method ◽  
Multiple Reflections ◽  
Step Method ◽  
Arrival Times ◽  
Sea Floor ◽  
Water Bottom

This paper discusses a two‐step method for predicting and attenuating multiple and peg‐leg reflections in unstacked seismic data. In the first step, an (observed) seismic record is extrapolated through a round‐trip traversal of the water layer, thus creating an accurate prediction of all possible multiples. In the second step, the record containing the predicted multiples is compared with and subtracted from the original. The wave‐equation method employed to predict the multiples takes accurate account of sea‐floor topography and so requires a precise water‐bottom profile as part of the input. Information about the subsurface below the sea floor is not required. The arrival times of multiple reflections are reproduced precisely, although the amplitudes are not accurate, and the sea floor is treated as a perfect reflector. The comparison step detects the similarities between the computed multiples and the original data, and estimates a transfer function to equalize the amplitudes and account for any change in waveform caused by the sea‐floor reflector. This two‐step wave‐equation method is effective even for dipping sea floors and dipping subsurface reflectors. It does not depend upon any assumed periodicity in the data or upon any difference in stacking velocity between primaries and multiples. Thus it is complementary to the less specialized methods of multiple suppression.

Case Study: Improving the quality of the seismic reflection image for a Fujian mineral exploration data set with offset-domain common-image gathers

Geophysics ◽  
2021 ◽  
pp. 1-45
Author(s):  
Guofeng Liu ◽  
Xiaohong Meng ◽  
Johanes Gedo Sea
Keyword(s):  
Wave Equation ◽  
Image Quality ◽  
Seismic Data ◽  
Seismic Reflection ◽  
Mineral Exploration ◽  
Velocity Model ◽  
Image Point ◽  
Single Shot ◽  
Data Set ◽  
Depth Migration

Seismic reflection is a proven and effective method commonly used during the exploration of deep mineral deposits in Fujian, China. In seismic data processing, rugged depth migration based on wave-equation migration can play a key role in handling surface fluctuations and complex underground structures. Because wave-equation migration in the shot domain cannot output offset-domain common-image gathers in a straightforward way, the use of traditional tools for updating the velocity model and improving image quality can be quite challenging. To overcome this problem, we employed the attribute migration method. This worked by sorting the migrated stack results for every single-shot gather into the offset gathers. The value of the offset that corresponded to each image point was obtained from the ratio of the original migration results to the offset-modulated shot-data migration results. A Gaussian function was proposed to map every image point to a certain range of offsets. This helped improve the signal-to-noise ratio, which was especially important in handing low quality seismic data obtained during mineral exploration. Residual velocity analysis was applied to these gathers to update the velocity model and improve image quality. The offset-domain common-image gathers were also used directly for real mineral exploration seismic data with rugged depth migration. After several iterations of migration and updating the velocity, the proposed procedure achieved an image quality better than the one obtained with the initial velocity model. The results can help with the interpretation of thrust faults and deep deposit exploration.

ADVANCES IN 3-D SEISMIC DATA PROCESSING TECHNIQUES

1992 ◽  
Vol 32 (1) ◽  
pp. 276
Author(s):  
T.J. Allen ◽  
P. Whiting
Keyword(s):  
Data Processing ◽  
Seismic Data ◽  
Three Dimensional ◽  
Velocity Model ◽  
Migration Velocity ◽  
Seismic Data Processing ◽  
Data Set ◽  
Migration Velocity Analysis ◽  
Processing Techniques ◽  
Made In

Several recent advances made in 3-D seismic data processing are discussed in this paper.Development of a time-variant FK dip-moveout algorithm allows application of the correct three-dimensional operator. Coupled with a high-dip one-pass 3-D migration algorithm, this provides improved resolution and response at all azimuths. The use of dilation operators extends the capability of the process to include an economical and accurate (within well-defined limits) 3-D depth migration.Accuracy of the migration velocity model may be improved by the use of migration velocity analysis: of the two approaches considered, the data-subsetting technique gives more reliable and interpretable results.Conflicts in recording azimuth and bin dimensions of overlapping 3-D surveys may be resolved by the use of a 3-D interpolation algorithm applied post 3-D stack and which allows the combined surveys to be 3-D migrated as one data set.

Dynamic time corrections and their application to seismic data over sea floor canyons in the Gippsland Basin

1989 ◽  
Vol 20 (2) ◽  
pp. 237 ◽  
Author(s):  
C.I. Blyth ◽  
N.J. Fisher ◽  
A.M. Heath
Keyword(s):  
Seismic Data ◽  
Seismic Reflection ◽  
Lateral Velocity ◽  
Sea Floor ◽  
Velocity Anomaly ◽  
Depth Maps ◽  
Dynamic Time ◽  
Push Down ◽  
Complex Ray ◽  
Gippsland Basin

Seismic reflection events beneath marked lateral velocity variations are distorted by complex ray paths. This can result in a stacked section with events that show poor continuity and are affected by 'pull up' or 'push down'. Where the velocity anomaly is not near the surface, conventional statics often fail to produce an adequate result.A pre-stack solution based on ray tracing is presented, which applies dynamic time corrections that vary with offset and travel time. The method was applied to a grid of data in the Gippsland Basin, affected by deep erosional canyons on the sea floor. The resulting sections generally showed significant improvement to the continuity of events thus enabling depth maps of greater accuracy to be constructed. We conclude that the method is more suitable in the study area than other pre-stack techniques given the absence of steep dips beneath the canyons and the exploration objectives. Other applications of the method are also mentioned.

Compensation of marine seismic data for the effects of highly variable water depth using ray‐trace modeling—A case history

Geophysics ◽  
1983 ◽  
Vol 48 (7) ◽  
pp. 910-933 ◽  
Author(s):  
Brian Dent
Keyword(s):  
Water Depth ◽  
Case History ◽  
Seismic Data ◽  
The Philippines ◽  
Sea Floor ◽  
Timing Errors ◽  
Static Corrections ◽  
Ray Trace ◽  
Marine Seismic ◽  
Variable Water

Variable water depth can cause severe degradation of marine seismic data. This paper presents a technique for correcting the effects of water depth variation and is a case history of applying the technique to a line of data from the Philippines offshore. The line crosses a deep submarine valley. It will be shown that when the water depth changes rapidly relative to the cable length, the timing variations introduced will not be static. They are dynamic, not static, because they differ for different event times of a single trace. To compensate for these dynamic timing variations, a two‐stage technique was used. A ray‐trace modeling program calculated the traveltimes to several depths, both for where the valley is present and where it is absent. A second program used the model results to shift the samples on all seismic traces to the time they would have if the valley were not present. The most difficult part of this project was finding a good model. The model is composed of two parts: the depth of the sea floor and the velocity‐depth relationships below the sea floor. The depth of the sea floor was estimated from the first arrivals on the near‐offset traces of the seismic data. This was difficult because of the shallowness of the normal sea floor (about 80 m) and the large offset between the shot and the first group (255 m). The first arrivals were head waves, not reflections, off the sea floor. The reflections from the valley had to be migrated to obtain accurate depths. The subsea velocity‐depth relations also had to be estimated from the seismic data. However, the results of applying the corrections calculated from this model to the data show a definite enhancement of reflector continuity; velocity semblance contour plots show the same enhancement. These results are contrasted with the results of applying purely static corrections. The static corrections also improve reflector continuity, but the dynamic corrections do a better job of it. Although the dynamic corrections improve a brute stack of the data, more importantly they allow additional processing to produce a much better final stack. Thus, the data were further processed to produce an optimal final stack. The dynamic corrections in particular allowed a much better choice of normal moveout (NMO) velocities near the valley. Also, a zone of near‐surface, high‐velocity material near the valley was detected by distortion of reflections on 100 percent shot records. Compensation for the zone was effected with a set of localized, static corrections. The data were also muted, band‐pass filtered, and dip filtered. Although the final stack is greatly improved, there is still a serious degradation of the data under the valley. This is because the valley not only introduces timing errors, but it also reduces the amplitude of the reflections returned from below it. The valley also introduces coherent noise in the form of scattering off its sides and enhanced multiples. These additional problems not only affect the final stack, but limit the accuracy with which the model can be built to correct the timing errors. Thus, corrections for the effects of highly variable water depth, preferably dynamic, are required in order to obtain the optimal stack of seismic data recorded over such a sea bottom. The difficulty in obtaining the corrections would be greatly reduced if accurate, closely spaced, fathometer measurements of water depth were made an integral part of marine seismic data recording.

Feasibility of CDP seismic reflection to image structures in a 220-m deep, 3-m thick coal zone near Palau, Coahuila, Mexico

Geophysics ◽  
1992 ◽  
Vol 57 (10) ◽  
pp. 1373-1380 ◽  
Author(s):  
Richard D. Miller ◽  
Victor Saenz ◽  
Robert J. Huggins
Keyword(s):  
Seismic Data ◽  
Seismic Reflection ◽  
Subsurface Structure ◽  
Reflection Method ◽  
Accurate Identification ◽  
Common Depth Point ◽  
Seismic Reflection Method ◽  
The Common ◽  
Zone Depth ◽  
Seismic Sections

The common‐depth‐point (CDP) seismic‐reflection method was used to delineate subsurface structure in a 3-m thick, 220-m deep coal zone in the Palau area of Coahuila, Mexico. An extensive series of walkaway‐noise tests was performed to optimize recording parameters and equipment. Reflection events can be interpreted from depths of approximately 100 to 300 m on CDP stacked seismic sections. The seismic data allow accurate identification of the horizontal location of the structure responsible for a drill‐discovered 3-m difference in coal‐zone depth between boreholes 150 m apart. The reflection method can discriminate folding with wavelengths in excess of 20 m and faulting with offset greater than 2 m at this site.

Accurate imaging of surface seismic data without a velocity model

2007 ◽  
Author(s):  
Sverre Brandsberg-Dahl ◽  
Brian E. Hornby ◽  
Xiang Xiao
Keyword(s):  
Seismic Data ◽  
Velocity Model ◽  
Accurate Imaging

scholarly journals Integrated magnetotelluric and seismic investigation of Cenozoic graben structure near Obrzycko, Poland

2021 ◽  
Author(s):  
Adam Cygal ◽  
Michał Stefaniuk ◽  
Anna Kret
Keyword(s):  
Seismic Data ◽  
Geophysical Methods ◽  
Geological Structure ◽  
Data Sets ◽  
Low Velocity ◽  
Shallow Subsurface ◽  
Geophysical Model ◽  
Novel Approach ◽  
Loose Deposits ◽  
Static Corrections

AbstractThis article presents the results of an integrated interpretation of measurements made using Audio-Magnetotellurics and Seismic Reflection geophysical methods. The obtained results were used to build an integrated geophysical model of shallow subsurface cover consisting of Cenozoic deposits, which then formed the basis for a detailed lithological and tectonic interpretation of deeper Mesozoic sediments. Such shallow covers, consisting mainly of glacial Pleistocene deposits, are typical for central and northern Poland. This investigation concentrated on delineating the accurate geometry of Obrzycko Cenozoic graben structure filled with loose deposits, as it was of great importance to the acquisition, processing and interpretation of seismic data that was to reveal the tectonic structure of the Cretaceous and Jurassic sediments which underly the study area. Previously, some problems with estimation of seismic static corrections over similar grabens filled with more recent, low-velocity deposits were encountered. Therefore, a novel approach to estimating the exact thickness of such shallow cover consisting of low-velocity deposits was applied in the presented investigation. The study shows that some alternative geophysical data sets (such as magnetotellurics) can be used to significantly improve the imaging of geological structure in areas where seismic data are very distorted or too noisy to be used alone

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