Estimation of layer parameters for linear P- and S-wave velocity functions

Geophysics ◽  
2007 ◽  
Vol 72 (3) ◽  
pp. U27-U30 ◽  
Author(s):  
Alexey Stovas ◽  
Bjørn Ursin
Keyword(s):  
Wave Velocity ◽  
Layered Medium ◽  
S Wave ◽  
Velocity Gradients ◽  
Zero Offset ◽  
Seismic Reflections

For a horizontally layered medium with isotropic layers with constant P- and S-wave velocity gradients, it is possible to estimate the velocity functions (gradient and velocity at the top of each layer) and thickness of each layer. From large-offset PP seismic reflections, one can estimate three traveltime parameters: the zero-offset two-way traveltime, the NMO velocity, and a heterogeneity coefficient responsible for the nonhyperbolicity of the traveltime curve, using the different traveltime approximations. From large-offset (offset/depth greater than two) PS seismic reflections, one can estimate two traveltime parameters: zero-offset two-way traveltime and NMO velocity. From the estimated traveltime parameters at the top and bottom of a layer, it is possible to compute the thickness and velocity functions of the layer.

Elastic-wavefield interferometry using P-wave source VSPs at the Wamsutter field, Wyoming

Geophysics ◽  
2012 ◽  
Vol 77 (2) ◽  
pp. Q27-Q36 ◽  
Author(s):  
James Gaiser ◽  
Ivan Vasconcelos ◽  
Rosemarie Geetan ◽  
John Faragher
Keyword(s):  
Stationary Phase ◽  
Wave Velocity ◽  
P Wave ◽  
Phase Point ◽  
S Wave ◽  
Wave Source ◽  
S Waves ◽  
Wave Splitting ◽  
Zero Offset ◽  
Tube Wave

In this study, elastic-wavefield interferometry was used to recover P- and S-waves from the 3D P-wave vibrator VSP data at Wamsutter field in Wyoming. S-wave velocity and birefringence is of particular interest for the geophysical objectives of lithology discrimination and fracture characterization in naturally fractured tight gas sand reservoirs. Because we rely on deconvolution interferometry for retrieving interreceiver P- and S-waves in the subsurface, the output fields are suitable for high-resolution, local reservoir characterization. In 1D media where the borehole is nearly vertical, data at the stationary-phase point is not conducive to conventional interferometry. Strong tube-wave noise generated by physical sources near the borehole interfere with S-wave splitting analyses. Also, converted P- to S-wave (PS-wave) polarity reversals occur at zero offset and cancel their recovery. We developed methods to eliminate tube-wave noise by removing physical sources at the stationary-phase point and perturbing the integration path in the integrand based on P-wave NMO velocity of the direct-arrival. This results in using nonphysical energy outside a Fresnel radius that could not have propagated between receivers. To limit the response near the stationary-phase point, we also applied a weighting condition to suppress energy from large offsets. For PS-waves, a derivative-like operator was applied to the physical sources at zero offset in the form of a polarity reversal. These methods resulted in effectively recovering P-wave dipole and PS-wave quadrupole pseudosource VSPs. The retrieved wavefields kinematically correspond to a vertical incidence representation of reflectivity/transmissivity and can be used for conventional P- and S-wave velocity analyses. Four-component PS-wave VSPs retrieve S-wave splitting in transmitted converted waves that provide calibration for PS-wave and P-wave azimuthal anisotropy measurements from surface-seismic data.

Some comments on common-asymptotic-conversion-point (CACP) sorting of converted-wave data in isotropic, laterally inhomogeneous media

Geophysics ◽  
2005 ◽  
Vol 70 (3) ◽  
pp. U29-U36 ◽  
Author(s):  
Mirko van der Baan
Keyword(s):  
Wave Velocity ◽  
Velocity Ratio ◽  
P Wave ◽  
Pure Mode ◽  
S Wave ◽  
Converted Wave ◽  
Wave Data ◽  
Conversion Point ◽  
Isotropic Media ◽  
Zero Offset

Common-midpoint (CMP) sorting of pure-mode data in arbitrarily complex isotropic or anisotropic media leads to moveout curves that are symmetric around zero offset. This greatly simplifies velocity determination of pure-mode data. Common-asymptotic-conversion-point (CACP) sorting of converted-wave data, on the other hand, only centers the apexes of all traveltimes around zero offset in arbitrarily complex but isotropic media with a constant P-wave/S-wave velocity ratio everywhere. A depth-varying CACP sorting may therefore be required to position all traveltimes properly around zero offset in structurally complex areas. Moreover, converted-wave moveout is nearly always asymmetric and nonhyperbolic. Thus, positive and negative offsets need to be processed independently in a 2D line, and 3D data volumes are to be divided in common azimuth gathers. All of these factors tend to complicate converted-wave velocity analysis significantly.

Geological variation in S-wave velocity structures in Northern Taiwan and implications for seismic hazards based on ambient noise analysis

2014 ◽  
Vol 96 ◽  
pp. 353-360
Author(s):  
Ya-Chuan Lai ◽  
Bor-Shouh Huang ◽  
Yu-Chih Huang ◽  
Huajian Yao ◽  
Ruey-Der Hwang ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Ambient Noise ◽  
Noise Analysis ◽  
Seismic Hazards ◽  
S Wave ◽  
Northern Taiwan

Structure of S-Wave Velocity in the Crust-Upper Mantle and Tectonic Setting of Strong Earthquakes Beneath Yunnan

2011 ◽  
Vol 54 (3) ◽  
pp. 286-298 ◽  
Author(s):  
Xiao-Man ZHANG ◽  
Jia-Fu HU ◽  
Yi-Li HU ◽  
Hai-Yan YANG ◽  
Jia CHEN ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Upper Mantle ◽  
Tectonic Setting ◽  
S Wave ◽  
Strong Earthquakes

The relation between seismic P‐ and S‐wave velocity dispersion in saturated rocks

Geophysics ◽  
1994 ◽  
Vol 59 (1) ◽  
pp. 87-92 ◽  
Author(s):  
Gary Mavko ◽  
Diane Jizba
Keyword(s):  
Wave Velocity ◽  
Large Scale ◽  
Velocity Dispersion ◽  
Seismic Velocity ◽  
Ultrasonic Velocities ◽  
S Wave ◽  
Local Flow ◽  
Wave Velocities ◽  
Shear Compliance

Seismic velocity dispersionin fluid-saturated rocks appears to be dominated by tow mecahnisms: the large scale mechanism modeled by Biot, and the local flow or squirt mecahnism. The tow mechanisms can be distuinguished by the ratio of P-to S-wave dispersions, or more conbeniently, by the ratio of dynamic bulk to shear compliance dispersions derived from the wave velocities. Our formulation suggests that when local flow denominates, the dispersion of the shear compliance will be approximately 4/15 the dispersion of the compressibility. When the Biot mechanism dominates, the constant of proportionality is much smaller. Our examination of ultrasonic velocities from 40 sandstones and granites shows that most, but not all, of the samples were dominated by local flow dispersion, particularly at effective pressures below 40 MPa.

A Method to Predict S-Wave Velocity from Wire-Line Logs for Organic- Rich Shales

2021 ◽  
Author(s):  
Z. Liu ◽  
J. Liu ◽  
Q. Bao ◽  
N. Dong ◽  
L. Shi ◽  
...  
Keyword(s):  
Wave Velocity ◽  
S Wave
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