Analysis of converted refractions for shear statics and near-surface characterisation

Meulenbroek, Alan; Hearn, Steve

doi:10.1071/eg10031

Cited by 7 publications

(5 citation statements)

References 12 publications

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“…The concepts introduced here provide the basis for a practical evaluation of converted-wave refraction, which is presented in a companion paper (Meulenbroek and Hearn, 2011).…”

Section: Discussionmentioning

confidence: 99%

“…In practice, however, the PPP estimate is preferred, because dip has less influence, and because the PPP arrivals are generally of higher quality (e.g. Meulenbroek and Hearn, 2011).…”

Section: Slope-intercept Interpretation For Pps Refractionmentioning

confidence: 99%

“…That is, the reduced refraction time derived from single-sided refraction data can be directly compared to the time-depth derived from reversed data. This approach of integrating time-depth and delay-time results is demonstrated in Meulenbroek and Hearn (2011).…”

Section: Relationship Between Time-depth and Delay-timementioning

confidence: 99%

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Ray-path concepts for converted-wave seismic refraction

Hearn

Meulenbroek

2011

Exploration Geophysics

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P-wave reflection-statics solutions typically incorporate P-wave refraction data, derived from the first breaks of the production data. Similarly, converted-wave refractions, taken from inline-component recordings, can be exploited to yield S-wave receiver statics, required in the processing of converted-wave reflection data. This methodology requires extensions to well known P-wave refraction analysis methods. This paper outlines extensions of the slope-intercept method and the reciprocal method, required to analyse converted-wave refractions. We discuss the computation of S-wave time-depths and describe how the observed ratio of S-wave to P-wave time-depths can provide a useful estimate of the near-surface V P /V S ratio, which is of interest in the analysis of engineering rock strengths.We also include discussion of several related practical issues, with particular reference to dynamite sources. When the source is buried in the refractor, the required reciprocal times cannot be directly measured from the raw travel-time data. They can, however, be easily derived via correction using measured intercept times. Often converted-wave refractions are of poorer quality than conventional P-wave refractions, such that reversed refractions may not be available over some parts of the spread. In this situation, the preferred time-depth quantity cannot be computed. However, delay-times derived from singleended data can be substituted, particularly if lateral variations in refractor velocity are allowed for.The concepts outlined here are used in a companion paper to correct S-wave receiver statics in a coal-scale dataset from the Bowen Basin in central Queensland.

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“…The concepts introduced here provide the basis for a practical evaluation of converted-wave refraction, which is presented in a companion paper (Meulenbroek and Hearn, 2011).…”

Section: Discussionmentioning

confidence: 99%

“…In practice, however, the PPP estimate is preferred, because dip has less influence, and because the PPP arrivals are generally of higher quality (e.g. Meulenbroek and Hearn, 2011).…”

Section: Slope-intercept Interpretation For Pps Refractionmentioning

confidence: 99%

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Ray-path concepts for converted-wave seismic refraction

Hearn

Meulenbroek

2011

Exploration Geophysics

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“…Note, however, that PS wave near-surface solutions are more complicated (e.g. Meulenbroek and Hearn, 2007) and therefore the PS results have more potential to vary from the constant weathering case. Finally, it is noted that the influence of the weathering layer might extend beyond static errors, as demonstrated here for the PS data.…”

Section: Ps Fresnel Radiusmentioning

confidence: 99%

“…For PS data the corresponding concept is to pick the PPS refraction (e.g. Hearn and Meulenbroek, 2011;Meulenbroek and Hearn, 2011). This event is generated by conversion of the critically refracting P wave to an upward travelling S headwave ( Figure 5.1).…”

Section: Pps Refraction Staticsmentioning

confidence: 99%

Resolution enhancement in shallow 3D-PS seismic reflection

Strong¹

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This thesis aims to advance methodology for acquiring and processing 3D multicomponent seismic data for shallow (< 300 m) exploration targets. The primary focus is to improve seismic resolution, and hence geological interpretation, for coal-scale targets.The coal industry is a significant contributor to the energy security and economy of Australia and the world. Conventional P-wave seismic methods are widely used in this industry, providing economic, safety and environmental benefits. There is potential for expanding these benefits by including multicomponent procedures. In this thesis, the primary focus is on converted-wave (PS) reflection, which is a logical extension to the standard approach. This has theoretical potential to provide extra geological information. It has also been proposed that there may be resolution advantages for shallower targets such as coal.A valuable starting point for understanding resolution in shallow P and PS reflection is via visco-elastic finite-difference simulation. This provides a useful indication of the reflection response of different targets, and can include the influence of different processing flows. For typical coal-scale environments, modelling with reasonable anelasticity assumptions suggests that PS resolution is unlikely to be superior to P resolution, even with idealised acquisition and processing. In real-world situations, achieving good PS resolution may be even more challenging. There are a number of factors across the acquisition and processing flow which incrementally influence resolution.Survey design is intrinsically more complex for PS surveys than for P, primarily because of ray-path asymmetry. In addition, phase and amplitude effects require careful analysis, and finite-difference modelling provides a useful tool. Such modelling suggests that for shallow surveys in particular, it may be possible to incorporate longer relative offsets, compared to the petroleum scale. An examination of bin fold, and offset/azimuth distribution, suggests that the natural bin size of a PS survey is mostly dependent on the receiver spacing, and is generally larger than for P waves. This favours the use of higher receiver densities for multicomponent surveys. These observations can be more important at the shallow scale, again because of greater ray-path asymmetry and potentially higher V P /V S value.One of the most critical steps in the shallow PS processing sequence is correcting for the S-wave receiver statics. Three relatively conventional approaches have been evaluated. A surface-consistent inversion approach has been shown to fail for shallow targets, or in the presence of strong noise. For our 3D data set, PPS refraction analysis provided the preferred solution. In other cases where PPS refractions are poorly defined, our robust statistical approach may be useful for determining short-wavelength statics, although additional long-wavelength control would then be needed.ii In exploration seismology, surface waves are commonly considered to be noise. However, the d...

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