Converted-wave moveout and conversion-point equations in layered VTI media: theory and applications

Li, Xiang‐Yang; Yuan, Jianxin

doi:10.1016/j.jappgeo.2003.02.001

Cited by 67 publications

(65 citation statements)

References 12 publications

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“…We have also shown that the VTI effects and the effects of the asymmetric raypath can be fully compensated for using the four-parameter theory of Li and Yuan (2003), which leads to an improvement in both imaging quality and event correlation between PP and PS converted-waves.…”

Section: Discussionmentioning

confidence: 91%

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Estimating anisotropic parameters from PS converted‐wave data: A case study

Wang

Dai

et al. 2006

SEG Technical Program Expanded Abstracts 2006

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Anisotropic parameters are estimated from PS converted-wave (C-wave) data. The data were acquired by digital MEMS (micro-electro-mechanical system) sensors over a volcanic gas reservoir in Northeast China with a mixed sand and shale sequence in the overburden. This gives rise to both shear-wave splitting and anisotropy moveout effects due to presence of vertical transverse isotropy (VTI). We use a four-parameter theory to evaluate the effects of non-hyperbolic moveout due to an asymmetric raypath and VTI. These four parameters include the PS converted wave stacking velocity (V C2 ), the vertical velocity ratio (γ 0 ), the effective velocity ratio (γ eff ), and the anisotropy parameter (χ eff ). This four-parameter theory leads to an improvement in imaging quality and correlation between the P-waves and converted-waves. After compensating for the VTI effects, we analyze the shear-wave splitting in the post stacked data. We find that the amount of splitting determined from the data can be correlated to the known gas reservoirs, and is also consistent with other amplitude and spectral anomalies associated with the gas reservoirs, revealing a potential for using shear-wave splitting to delineate gas reservoirs in volcanic rocks.

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Section: Discussionmentioning

confidence: 91%

“…According to Li and Yuan (2003), four parameters are required to perform converted-wave velocity analysis and moveout…”

Section: Estimating Anisotropic Parameters For Vtimentioning

confidence: 99%

Estimating anisotropic parameters from PS converted‐wave data: A case study

Wang

Dai

et al. 2006

SEG Technical Program Expanded Abstracts 2006

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“…For anisotropic media, the migration velocity model consists of PS converted wave velocity ( ps V ), vertical velocity ratio ( 0 γ ), effective velocity ratio ( eff γ ) and the anisotropic parameters ( χ ) (Li, et al, 2007;Li and Yuan 2003).…”

Section: Effects Of Travel-time Errors On Prestack Time Migrationmentioning

confidence: 99%

“…This phenomenon is useful for processing PS converted wave data because it is difficult and time-consuming to estimate the P-to-S velocity ratio accurately from real data. However, when anisotropy cannot be neglected, there are more parameters in the velocity model of PS converted waves (Li and Crampin, 1993;Li and Yuan 2003). We have to investigate the effects of errors in these parameters on the traveltime and imaging of PS converted waves.…”

Section: Introductionmentioning

confidence: 99%

Effect of errors in the migration velocity model of PS-converted waves on traveltime accuracy in prestack Kirchhoff time migration in weak anisotropic media

Dai

2008

GEOPHYSICS

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We investigate the effect of errors in the migration velocity model of PS converted waves on the travel-time calculated in prestack Kirchhoff time migration in weak anisotropic media.The prestack Kirchhoff time migration operator contains four parameters: PS converted wave velocity, vertical velocity ratio, effective velocity ratio, and anisotropic parameter. We derive four error factors corresponding to the four parameters, respectively. Theoretical and numerical analyses of the error factors show that all the error factors are inversely proportional to the velocity as well as to the travel-time. Errors in travel-time for shallow events are usually larger than those for deep events. The error in the PS converted wave velocity causes the largest error in the travel-time, and the error in the vertical velocity ratio causes the smallest error in the travel time. The error in effective velocity ratio has a larger effect on the travel-time than the error in anisotropic parameter when the ratio of horizontal distance to depth is small. However, the error in anisotropic parameter has a large effect on travel-time than the error in effective velocity ratio when the ratio of horizontal distance to depth is lager. The errors in the travel time caused by errors in effective velocity ratio and anisotropy parameter stem mainly from the converted S-wave raypath of the PS converted waves. For time processing, it is possible to estimate PS-wave velocity accurately without accurate information of vertical velocity ratio, effective velocity ratio and anisotropic parameter. This can save processing cost and time. These findings are useful both for our understanding of PS-wave behaviour and for PS-wave imaging in anisotropic media.Dai and Li: Error effect in PKTM for anisotropic media 2

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“…Therefore, for the target formation, the non-hyperbolic effects are relatively weak. According to Li and Yuan (2003), both the non-hyperbolic moveout and the positioning error due to the asymmetry raypath are small and may be neglected for offsetdepth ratio less than one. Therefore in this case, noise and statics are the main issue for processing the converted-wave data.…”

Section: Data Processingmentioning

confidence: 99%

PP and PS seismic response from fractured tight gas reservoirs: a case study

Jianming¹,

Zhang²,

Li³

2008

J. Geophys. Eng.

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In this paper, we present an example of using PP and PS converted-wave data recorded by digital MEMS (micro-eletro-mechanical-system) to evaluate a fractured tight gas reservoir from the Xinchang gas field in Sichuan China. For this, we analyze the variations in converted shear-wave splitting, Vp/Vs ratio and PP and PS impedance, as well as other attributes based on absorption and velocity dispersion. The reservoir formation is tight sandstone, buried at a depth of about 5000m, and the converted-wave data reveal significant shear-wave splitting over the reservoir formation. We utilize a rotation technique to extract the shear-wave polarization and time delay from the data, and a small-window correlation method to build time-delay spectra that allow the generation of a time-delay section. At the reservoir formation, the shear-wave time-delay is measured at 20ms, about 15% shear-wave anisotropy, correlating with the known gas reservoirs. Furthermore, the splitting anomalies are consistent with the characteristics of other attributes such as Vp/Vs ratio and P-and S-wave acoustic and elastic impedance. The P-wave shows consistent low impedance over the reservoir formation, whilst the S-wave impedance shows relatively high impedance. The calculated gas indicator based on absorption and velocity dispersion yields a high correlation with the gas bearing formations.This confirms the benefit of multicomponent seismic data from digital MEMS sensors.

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Converted-wave moveout and conversion-point equations in layered VTI media: theory and applications

Cited by 67 publications

References 12 publications

Estimating anisotropic parameters from PS converted‐wave data: A case study

Estimating anisotropic parameters from PS converted‐wave data: A case study

Effect of errors in the migration velocity model of PS-converted waves on traveltime accuracy in prestack Kirchhoff time migration in weak anisotropic media

PP and PS seismic response from fractured tight gas reservoirs: a case study

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