Azimuthal anisotropy of seismic velocity, attenuation andQ value in viscous EDA media

2000 ◽  
Vol 43 (1) ◽  
pp. 17-22 ◽  
Author(s):  
Zhongjie Zhang ◽  
Jiwen Teng ◽  
Zhenhua He
Keyword(s):  
Seismic Velocity ◽  
Azimuthal Anisotropy ◽  
Velocity Attenuation

scholarly journals Petrophysical constraints on the seismic properties of the Kaapvaal craton mantle root

2013 ◽  
Vol 5 (2) ◽  
pp. 963-1005 ◽  
Author(s):  
V. Baptiste ◽  
A. Tommasi
Keyword(s):  
Seismic Anisotropy ◽  
Seismic Velocity ◽  
Body Wave ◽  
Azimuthal Anisotropy ◽  
Mantle Xenoliths ◽  
P Wave ◽  
Kaapvaal Craton ◽  
Compositional Heterogeneity ◽  
P Waves ◽  
Seismic Properties

Abstract. We calculated the seismic properties of 47 mantle xenoliths from 9 kimberlitic pipes in the Kaapvaal craton based on their modal composition, the crystal preferred orientations (CPO) of olivine, ortho- and clinopyroxene, and garnet, the Fe content of olivine, and the pressures and temperatures at which the rocks were equilibrated. These data allow constraining the variation of seismic anisotropy and velocities with depth. The fastest P wave and fast split shear wave (S1) polarization direction is always close to olivine [100] maximum. Changes in olivine CPO symmetry result in minor variations in the seismic anisotropy patterns. Seismic anisotropy is higher for high olivine contents and stronger CPO. Maximum P waves azimuthal anisotropy (AVp) ranges between 2.5 and 10.2% and S waves polarization anisotropy (AVs) between 2.7 and 8%. Seismic properties averaged in 20 km thick intervals depth are, however, very homogeneous. Based on these data, we predict the anisotropy that would be measured by SKS, Rayleigh (SV) and Love (SH) waves for 5 end-member orientations of the foliation and lineation. Comparison to seismic anisotropy data in the Kaapvaal shows that the coherent fast directions, but low delay times imaged by SKS studies and the low azimuthal anisotropy and SH faster than SV measured using surface waves may only be consistently explained by dipping foliations and lineations. The strong compositional heterogeneity of the Kaapvaal peridotite xenoliths results in up to 3% variation in density and in up to 2.3% of variation Vp, Vs and the Vp/Vs ratio. Fe depletion by melt extraction increases Vp and Vs, but decreases the Vp/Vs ratio and density. Orthopyroxene enrichment decreases the density and Vp, but increases Vs, strongly reducing the Vp/Vs ratio. Garnet enrichment increases the density, and in a lesser manner Vp and the Vp/Vs ratio, but it has little to no effect on Vs. These compositionally-induced variations are slightly higher than the velocity perturbations imaged by body-wave tomography, but cannot explain the strong velocity anomalies reported by surface wave studies. Comparison of density and seismic velocity profiles calculated using the xenoliths' compositions and equilibrium conditions to seismological data in the Kaapvaal highlights that: (i) the thickness of the craton is underestimated in some seismic studies and reaches at least 180 km, (ii) the deep sheared peridotites represent very local modifications caused and oversampled by kimberlites, and (iii) seismological models probably underestimate the compositional heterogeneity in the Kaapvaal mantle root, which occurs at a scale much smaller than the one that may be sampled seismologically.

Azimuthal anisotropy analysis applied to naturally fractured unconventional reservoirs: A Barnett Shale example

2020 ◽  
Vol 8 (4) ◽  
pp. SP13-SP29
Author(s):  
Jing Zhang ◽  
Jie Qi ◽  
Yijin Zeng ◽  
Kurt Marfurt ◽  
Roger Slatt
Keyword(s):  
Stress Field ◽  
Reservoir Characterization ◽  
Seismic Velocity ◽  
Peak Frequency ◽  
Azimuthal Anisotropy ◽  
P Wave ◽  
Field Analysis ◽  
Velocity Variation ◽  
Barnett Shale ◽  
Natural Fractures

Studying the seismic responses of velocity and amplitude on wide-/full-azimuth seismic data is now common for unconventional reservoir characterization. Velocity variation with azimuth (VVAz) and amplitude variation with azimuth (AVAz) are two of the most popular tools to map not only the relative intensity and orientation of natural fractures but also the strength and orientation of the maximum horizontal stress SH. We prestack time migrated a wide-azimuth Barnett Shale survey in North Texas into eight azimuths and reduced noise on the gathers using prestack structure-oriented filtering. We then computed the envelope, spectral peak frequency, and prestack P-wave impedance attributes for each azimuthally limited seismic volume. We compensated the VVAz effects by flattening each sector along the Barnett Shale key horizons, thereby registering the gathers for subsequent AVAz analysis. The results indicate the intensity, orientation, and confidence of azimuthal anisotropy effects on seismic velocity and amplitude, which can be referred to smaller scale vertical cracks or natural fractures. Our analysis reveals four zones of high anisotropy intensity that can be tied to either the regional structures or paleo stress field. Analysis of production data indicate from the anisotropy interpretation results that vertical, sealed fractures are the dominant cause of anisotropy and those specific fractures inhibit production. This observation and results indicate that horizon-based azimuthal anisotropy analysis avoids the VVAz effect and can be applied to fractures and regional stress field prediction.

Elliptical dip moveout for 3D seismic imaging in the presence of azimuthal anisotropy

Geophysics ◽  
2012 ◽  
Vol 77 (1) ◽  
pp. C1-C12 ◽  
Author(s):  
Jeffrey Shragge ◽  
David Lumley
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Azimuthal Velocity ◽  
Azimuthal Anisotropy ◽  
Velocity Estimation ◽  
Velocity Anisotropy ◽  
Energy Formula ◽  
Geophysical Imaging ◽  
Processing Techniques

Seismic images of the earth’s interior can be significantly distorted by complex wave propagation effects arising from 3D structural velocity variations, combined with the presence of azimuthal velocity anisotropy within some of the rock layers. Most image-processing techniques attempt to separate and compensate for both of these phenomena sequentially; they rarely address both simultaneously. These approaches implicitly assume that the effects of 3D structural velocity and azimuthal anisotropy are separable, whereas in fact, both effects are coupled together in the seismic data. In the presence of strong azimuthal velocity anisotropy, this can lead to significant errors in seismic velocity estimation and degraded quality of subsurface images, especially for large source-receiver offsets, wide azimuths, and steep geologic dips. Such imaging errors can greatly increase the uncertainty associated with exploring, characterizing, developing and monitoring subsurface geologic features for hydrocarbons, geothermal energy, [Formula: see text] sequestration, and other important geophysical imaging applications. Our approach simultaneously addressed velocity structure and azimuthal anisotropy by development of an elliptic dip moveout (DMO) operator. We combined the structural-velocity insensitivity of isotropic DMO with elliptic moveout representative of azimuthal velocity anisotropy. Forward and adjoint elliptical DMO operators were then cascaded together to form a single elliptical moveout (EMO) operation, which had a skewed saddle-like impulse response that resembles an isotropic azimuthal moveout operator. The EMO operator can be used as a prestack data conditioner, to estimate azimuthal anisotropy in a domain that is relatively insensitive to 3D velocity structure, or to compensate and map the data back to its original prestack domain in its approximately equivalent isotropic wavefield form. We demonstrated that EMO can reduce structural dip image errors of 10°–20° or more for realistic azimuthal velocity anisotropy values at far offsets.

Seismic velocities of halite salt: Anisotropy, heterogeneity, dispersion, temperature, and pressure effects

Geophysics ◽  
2016 ◽  
Vol 81 (4) ◽  
pp. D293-D301 ◽  
Author(s):  
Fuyong Yan ◽  
De-hua Han ◽  
Qiuliang Yao ◽  
Xue-Lian Chen
Keyword(s):  
Model Building ◽  
Seismic Velocity ◽  
Azimuthal Anisotropy ◽  
Crystal Defects ◽  
Pressure Effects ◽  
P Wave ◽  
Seismic Exploration ◽  
Experimental Investigations ◽  
Stress Effect ◽  
Seismic Velocities

We have made various experimental investigations on rock-physics properties of the halite salt coming from a salt dome in the U.S. Gulf Coast Basin. The effect of crystal defects and intercrystal cracks on the P-wave velocity of the halite salt sample can be mitigated after high-pressure annealing. The temperature effect on seismic velocities of halite salt is dominant relative to the stress effect. Azimuthal anisotropy is not observed on the halite salt samples. We have observed that the velocity variations in different directions were mostly caused by the crystal-scale heterogeneity. For the salt structures primarily made of creep-deformed halite, the effect of seismic velocity anisotropy might be negligible for seismic exploration. No significant dispersion of seismic velocities was observed from the low-frequency measurement. Our measurements supply basic information for seismic velocity model building that may help to improve seismic imaging of salt structures.

Global imaging of the lithosphere-asthenosphere system

2020 ◽  
Author(s):  
Eric Debayle ◽  
Yanick Ricard ◽  
Stéphanie Durand ◽  
Thomas Bodin
Keyword(s):  
Large Scale ◽  
Seismic Velocity ◽  
3D Models ◽  
Azimuthal Anisotropy ◽  
Plate Motion ◽  
Effect Of Temperature ◽  
Mantle Flow ◽  
Simultaneous Interpretation ◽  
Velocity Models ◽  
Scale Properties

<p>Massive surface wave datasets constrain upper mantle seismic heterogeneities with horizontal wavelengths larger than 1000 km, allowing us to investigate the large-scale properties and alignment of olivine crystals in the lithosphere and asthenosphere. The azimuthal anisotropy projected onto the direction of present plate motion shows a very specific relation with the plate velocity. Plate-scale present-day deformation is remarkably well and uniformly recorded beneath plates moving faster than ∼4 cm/yr. Recent geodynamic models suggest that cold sinking instabilities tilted in the direction opposite to plate motion below fast plates could produce a pattern of large-scale azimuthal anisotropy consistent with our observations. Beneath slower plates, plate-motion aligned anisotropy is only observed locally, which suggests that the lithospheric motion does not control mantle flow below these plates.</p><p>Radial anisotropy extends deeper beneath continents than beneath oceans, but we find no such difference for azimuthal anisotropy, suggesting that beneath most continents, the alignment of olivine crystal is preferentially horizontal and azimuthally random at large scale. As most continents are located on slow moving plates, this supports the idea that azimuthal anisotropy aligns at large scale with the present plate motion only for plates moving faster than ∼4 cm/yr.</p><p>The same inversion also provides 3D models of seismic velocity and attenuation. The simultaneous interpretation of global 3D shear attenuation and velocity models has a great potential to decipher the effect of temperature, melt and composition on seismic observables. We will discuss our findings from the simultaneous interpretation of our latest models.</p>

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