To: “Reflection shear‐wave data collected near the principal axes of azimuthal anisotropy” by H. B. Lynn and L. A. Thomsen (GEOPHYSICS, 55, 147–156, February 1990)

Geophysics ◽  
1990 ◽  
Vol 55 (7) ◽  
pp. 948-948
Keyword(s):  
Shear Wave ◽  
Azimuthal Anisotropy ◽  
Wave Data ◽  
Principal Axes

Figure 12 in our paper is not complete. Unfortunately, the top part was cut off and all the words do not appear. The entire illustration is shown here with caption.

Layer‐stripping of azimuthal anisotropy from reflection shear‐wave data

1995 ◽  
Author(s):  
Leon Thomsen ◽  
Ilya Tsvankin ◽  
Michael C. Mueller
Keyword(s):  
Shear Wave ◽  
Azimuthal Anisotropy ◽  
Wave Data

Reflection shear‐wave data collected near the principal axes of azimuthal anisotropy

Geophysics ◽  
1990 ◽  
Vol 55 (2) ◽  
pp. 147-156 ◽  
Author(s):  
H. B. Lynn ◽  
L. A. Thomsen
Keyword(s):  
Reflection Coefficient ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Azimuthal Anisotropy ◽  
Display Time ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Reflection Amplitude ◽  
Principal Axes

The presence of vertically oriented fractures and/or unequal horizontal stresses has created an azimuthally anisotropic earth, in which shear‐wave (SH) data collected along the principal axes of the anisotropy display time and reflection amplitude anomalies. Amoco shot two crossing shear‐wave (SH) lines that were approximately parallel to the orthogonal principal axes of the azimuthal anisotropy. At the tie point, these crossing SH lines display a time‐variant mis‐tie. The tie point also displays reflection‐coefficient anomalies, attributable to azimuthally dependent shear‐wave velocities. Field mapping documented a set of fractures striking N69E which are approximately parallel to the line that exhibited greater traveltimes. Time‐variant mis‐ties and reflection coefficient anomalies are two of the seismic responses theoretically expected of an azimuthally anisotropic earth, i.e., one in which the shear‐wave velocity depends upon the polarization azimuth of the shear wave.

Evaluation of 3C microelectromechanical system data on a 2D line: Direct comparison with conventional vertical-component geophone arrays and PS-wave analysis

Geophysics ◽  
2011 ◽  
Vol 76 (3) ◽  
pp. B79-B87 ◽  
Author(s):  
Christian Stotter ◽  
Erika Angerer
Keyword(s):  
Shear Wave ◽  
Random Noise ◽  
Vertical Component ◽  
Azimuthal Anisotropy ◽  
P Wave ◽  
High Porosity ◽  
Vienna Basin ◽  
Data Set ◽  
Microelectromechanical System ◽  
Wave Data

A 2D vibroseis line was acquired in the Vienna Basin (Austria) for the purpose of comparing the data of digital multicomponent single sensors based on microelectromechanical system (MEMS) sensors alongside conventional vertical-component geophone arrays. For efficient removal of coherent noise during processing, all source points were recorded in single-sweep mode, i.e., no vertical stacking was performed in the field. On this densely sampled data set, several noise-reduction techniques, such as digital array forming, frequency-wavenumber (f-k) filtering in shot and receiver domains, and polarization filters, proved to be valuable in reducing source-generated noise. The results showed that, with the use of single-sweep recording and polarization filter techniques, it is possible to produce seismic sections for a single-receiver three-component (3C) MEMS line that are comparable to a conventional geophone array line in signal-to-noise ratio. However, the higher number of single geophones and hence the stronger attenuation of random noise in the conventional array resulted in an advantage for the analog geophone data set. The second goal for this survey was to evaluate additional information contained in the horizontal components of the MEMS data. The multicomponent data allowed for the processing of mode-converted shear-wave data, performed for the first time in the Vienna Basin. Azimuthal anisotropy related to horizontal stresses was observed in the Neogene section of the shear-wave data set. A PP-PS event correlation allowed the identification of major shallow horizons. Interpretation of the final sections confirmed that the PS data are useful to distinguish between gas reservoirs and high-porosity water sands, which can cause similar P-wave amplitude variation with offset (AVO) effects.

Coarse‐layer stripping of vertically variable azimuthal anisotropy from shear‐wave data

Geophysics ◽  
1999 ◽  
Vol 64 (4) ◽  
pp. 1126-1138 ◽  
Author(s):  
Leon Thomsen ◽  
Ilya Tsvankin ◽  
Michael C. Mueller
Keyword(s):  
Shear Wave ◽  
Synthetic Data ◽  
Azimuthal Anisotropy ◽  
High Fracture ◽  
Restrictive Assumption ◽  
Data Set ◽  
Wave Data ◽  
Shear Modes ◽  
Vsp Data ◽  
Attenuation And Dispersion

Alford rotation analysis of 2C × 2C shear‐wave data (two source components, two receiver components) for azimuthal anisotropy is valid only when the orientation of that azimuthal anisotropy is invariant with depth. The Winterstein and Meadows method of layer stripping vertical seismic profiling (VSP) data relaxes this restriction for coarse‐layer variation of the orientation of the anisotropy. Here we present a tensor generalization of the conventional convolutional model of scalar wave propagation and use it to derive generalizations of Winterstein and Meadows layer stripping, valid for 2C × 2C data and for the restricted 2C-only case, in the VSP and reflection contexts. In the 2C × 2C VSP application, the result reduces to that of Winterstein and Meadows in the case where both fast and slow shear modes have the same attenuation and dispersion; otherwise, a balancing of mode spectra and amplitudes is required. The 2C × 2C reflection result differs from the 2C × 2C VSP result since two applications of the mode‐balancing and mode‐advance operations are required (since the waves travel up as well as down). Application to a synthetic data set confirms these results. The 2C × 2C reflection algorithm enables the exploration for sweet spots of high fracture intensity ahead of the bit without the restrictive assumption that the anisotropy orientation is depth invariant.

Direct shear-wave seismic survey in Sanhu area, Qaidam Basin, west China

2022 ◽  
Vol 41 (1) ◽  
pp. 47-53
Author(s):  
Zhiwen Deng ◽  
Rui Zhang ◽  
Liang Gou ◽  
Shaohua Zhang ◽  
Yuanyuan Yue ◽  
...  
Keyword(s):  
Shear Wave ◽  
Reservoir Characterization ◽  
Qaidam Basin ◽  
P Wave ◽  
Data Sets ◽  
Direct Shear ◽  
Subsurface Structure ◽  
S Wave ◽  
West China ◽  
Wave Data

The formation containing shallow gas clouds poses a major challenge for conventional P-wave seismic surveys in the Sanhu area, Qaidam Basin, west China, as it dramatically attenuates seismic P-waves, resulting in high uncertainty in the subsurface structure and complexity in reservoir characterization. To address this issue, we proposed a workflow of direct shear-wave seismic (S-S) surveys. This is because the shear wave is not significantly affected by the pore fluid. Our workflow includes acquisition, processing, and interpretation in calibration with conventional P-wave seismic data to obtain improved subsurface structure images and reservoir characterization. To procure a good S-wave seismic image, several key techniques were applied: (1) a newly developed S-wave vibrator, one of the most powerful such vibrators in the world, was used to send a strong S-wave into the subsurface; (2) the acquired 9C S-S data sets initially were rotated into SH-SH and SV-SV components and subsequently were rotated into fast and slow S-wave components; and (3) a surface-wave inversion technique was applied to obtain the near-surface shear-wave velocity, used for static correction. As expected, the S-wave data were not affected by the gas clouds. This allowed us to map the subsurface structures with stronger confidence than with the P-wave data. Such S-wave data materialize into similar frequency spectra as P-wave data with a better signal-to-noise ratio. Seismic attributes were also applied to the S-wave data sets. This resulted in clearly visible geologic features that were invisible in the P-wave data.

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