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Journal articles on the topic 'Azimuthal anisotropy'

Author: Grafiati

Published: 4 June 2021

Last updated: 25 July 2025

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1

Al‐Dajani, Abdulfattah, and Tariq Alkhalifah. "Reflection moveout inversion for horizontal transverse isotropy: Accuracy, limitation, and acquisition." GEOPHYSICS 65, no. 1 (2000): 222–31. http://dx.doi.org/10.1190/1.1444713.

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Horizontal transverse isotropy (HTI) is the simplest azimuthally anisotropic model used to describe vertical fracturing in an isotropic matrix. Assuming that the subsurface is laterally homogeneous, and using the elliptical variation of P-wave NMO velocity with azimuth measured in at least three different source‐to‐receiver orientations, we can estimate three key parameters of HTI media: the vertical velocity, anisotropy, and the azimuth of the symmetry axis. Such parameter estimation is sensitive to the angular separation between the survey lines in 2-D acquisition or, equivalently, to source

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2

Kolesnikov, YuI, K. V. Fedin, and L. Ngomayezwe. "Compression waves reflection from the low-velocity azimuthally anisotropic medium: a physical model study." Geophysical Journal International 221, no. 2 (2020): 1320–26. http://dx.doi.org/10.1093/gji/ggaa031.

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SUMMARY Interest in azimuthal anisotropy of rocks is mainly associated with fractured reservoirs, which may contain hydrocarbon deposits. Cracks in such deposits in most cases have a subvertical orientation, which is caused by the predominance of vertical stresses in rocks over horizontal ones. To determine the azimuthal direction of fractures, one can use, in particular, the dependence of the reflection coefficients of elastic waves on the boundaries with such media on the azimuth. This paper presents the results of physical modelling, demonstrating this dependence. To conduct experiments, we

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3

Mallick, Subhashis, Kenneth L. Craft, Laurent J. Meister, and Ronald E. Chambers. "Determination of the principal directions of azimuthal anisotropy from P-wave seismic data." GEOPHYSICS 63, no. 2 (1998): 692–706. http://dx.doi.org/10.1190/1.1444369.

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In an azimuthally anisotropic medium, the principal directions of azimuthal anisotropy are the directions along which the quasi-P- and the quasi-S-waves propagate as pure P and S modes. When azimuthal anisotropy is induced by oriented vertical fractures imposed on an azimuthally isotropic background, two of these principal directions correspond to the directions parallel and perpendicular to the fractures. S-waves propagating through an azimuthally anisotropic medium are sensitive to the direction of their propagation with respect to the principal directions. As a result, primary or mode‐conve

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4

Gavin, Lisa J., and David Lumley. "The effects of azimuthal anisotropy on 3D and 4D seismic amplitude variation with offset responses." GEOPHYSICS 84, no. 6 (2019): C251—C267. http://dx.doi.org/10.1190/geo2018-0450.1.

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Seismic reflection amplitude variation with source-receiver offset (AVO) is an important tool in hydrocarbon exploration and reservoir monitoring, due to its sensitivity to elastic rock properties that are affected by changes in pore-fluid saturation and pressure. In most cases, 4D seismic feasibility studies and interpretation analyses assume that the earth is isotropic. This assumption can be problematic because it is becoming increasingly apparent that anisotropic rocks are quite common. Furthermore, the presence of even small amounts of anisotropy can have significant effects on AVO, and i

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5

Birdus, Sergey, Erika Angerer, and Iftikhar Abassi. "MAZ depth-velocity modelling and imaging with azimuthal anisotropy." APPEA Journal 50, no. 2 (2010): 723. http://dx.doi.org/10.1071/aj09087.

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Processing of multi and wide-azimuth seismic data faces some new challenges, and one of them is depth-velocity modelling and imaging with azimuthal velocity anisotropy. Analysis of multi-azimuth data very often reveals noticeable fluctuations in moveout between different acquisition directions. They can be caused by several factors: real azimuthal interval velocity anisotropy associated with quasi-vertical fractures or present day stress field within the sediments; short-wavelength velocity heterogeneities in the overburden; TTI (or VTI) anisotropy in the overburden; or, random distortions due

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6

Koren, Zvi, and Igor Ravve. "Fourth-order normal moveout velocity in elastic layered orthorhombic media — Part 2: Offset-azimuth domain." GEOPHYSICS 82, no. 3 (2017): C113—C132. http://dx.doi.org/10.1190/geo2016-0222.1.

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Based on the theory derived in part 1, in which we obtained the azimuthally dependent fourth-order normal-moveout (NMO) velocity functions for layered orthorhombic media in the slowness-azimuth/slowness and the slowness-azimuth/offset domains, in part 2, we extend the theory to the offset-azimuth/slowness and offset-azimuth/offset domains. We reemphasize that this paper does not suggest a new nonhyperbolic traveltime approximation; rather, it provides exact expressions of the NMO series coefficients, computed for normal-incidence rays, which can then be further used within known azimuthally de

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7

Xu, Song, Xiao-Ming Tang, Carlos Torres-Verdín, Zhen Li, and Yuanda Su. "Evaluation of 3D shear-wave anisotropy based on elastic-wave velocity variations around the borehole." GEOPHYSICS 86, no. 3 (2021): D103—D112. http://dx.doi.org/10.1190/geo2020-0523.1.

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Aligned fractures/cracks in rocks are a primary source of elastic anisotropy. In an azimuthally anisotropic formation surrounding a borehole, shear-waves (S-waves) split into fast and slow waves that propagate along the borehole and are recorded by a borehole logging tool. However, when the formation has conjugate fractures with orthogonal strike directions, the azimuthal anisotropy vanishes. Hence, azimuthal anisotropy measurements may not be adequate to detect orthogonal fracture sets. We have developed a method for obtaining azimuthal and radial S-wave anisotropy parameters simultaneously f

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8

Gavin, Lisa J., and David Lumley. "Stress-induced seismic azimuthal anisotropy, sand-shale content, and depth trends offshore North West Australia." GEOPHYSICS 82, no. 2 (2017): C77—C90. http://dx.doi.org/10.1190/geo2015-0709.1.

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Seismic azimuthal anisotropy is apparent when P-wave velocities vary with source-receiver azimuth and downward-propagating S-waves split into two quasi-S-waves, polarized in orthogonal directions. Not accounting for these effects can degrade seismic image quality and result in erroneous amplitude analysis and geologic interpretations. There are currently no physical models available to describe how azimuthal anisotropy induced by differential horizontal stress varies with sand-shale lithology and depth; we develop a model that does so, in unconsolidated sand-shale sequences offshore North West

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9

Zhang, Jing, Jie Qi, Yijin Zeng, Kurt Marfurt, and Roger Slatt. "Azimuthal anisotropy analysis applied to naturally fractured unconventional reservoirs: A Barnett Shale example." Interpretation 8, no. 4 (2020): SP13—SP29. http://dx.doi.org/10.1190/int-2019-0206.1.

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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 t

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10

Lynn, H. B., and L. A. Thomsen. "Reflection shear‐wave data collected near the principal axes of azimuthal anisotropy." GEOPHYSICS 55, no. 2 (1990): 147–56. http://dx.doi.org/10.1190/1.1442821.

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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. Fie

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11

Xu, Xiaoxia, Ilya Tsvankin, and Andrés Pech. "Geometrical spreading of P-waves in horizontally layered, azimuthally anisotropic media." GEOPHYSICS 70, no. 5 (2005): D43—D53. http://dx.doi.org/10.1190/1.2052467.

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For processing and inverting reflection data, it is convenient to represent geometrical spreading through the reflection traveltime measured at the earth's surface. Such expressions are particularly important for azimuthally anisotropic models in which variations of geometrical spreading with both offset and azimuth can significantly distort the results of wide-azimuth amplitude-variation-with-offset (AVO) analysis. Here, we present an equation for relative geometrical spreading in laterally homogeneous, arbitrarily anisotropic media as a simple function of the spatial derivatives of reflectio

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12

Xu, Xiaoxia, and Ilya Tsvankin. "Anisotropic geometrical-spreading correction for wide-azimuth P-wave reflections." GEOPHYSICS 71, no. 5 (2006): D161—D170. http://dx.doi.org/10.1190/1.2335615.

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Compensation for geometrical spreading along a raypath is one of the key steps in AVO (amplitude-variation-with-offset) analysis, in particular, for wide-azimuth surveys. Here, we propose an efficient methodology to correct long-spread, wide-azimuth reflection data for geometrical spreading in stratified azimuthally anisotropic media. The P-wave geometrical-spreading factor is expressed through the reflection traveltime described by a nonhyperbolic moveout equation that has the same form as in VTI (transversely isotropic with a vertical symmetry axis) media. The adapted VTI equation is paramet

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13

Burnett, William, and Sergey Fomel. "3D velocity-independent elliptically anisotropic moveout correction." GEOPHYSICS 74, no. 5 (2009): WB129—WB136. http://dx.doi.org/10.1190/1.3184804.

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Azimuthal anisotropy or lateral velocity variations cause azimuthal variations in moveout velocity, which can degrade seismic images if handled improperly. In cases in which apparent azimuthally anisotropic moveout is present, a single picked velocity is inadequate to flatten an event on a 3D CMP gather. Conventional velocity-analysis techniques require a significant amount of time and effort, especially in areas where apparent anisotropy is observed. We propose a velocity-independent imaging approach to perform an elliptically anisotropic moveout correction in three dimensions. The velocity-i

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14

Corchete, Víctor. "Azimuthal Variation in the Surface Wave Velocity of the Philippine Sea Plate." Journal of Marine Science and Engineering 13, no. 3 (2025): 606. https://doi.org/10.3390/jmse13030606.

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A study of the azimuthal variation in the surface wave fundamental-mode phase velocity is performed for the Philippine Sea Plate (PSP). This azimuthal variation has been anisotropically inverted for the PSP to determine the isotropic and anisotropic structure of this plate from 0 to 260 km. This azimuthal variation is due to anisotropy in the upper mantle. The crust is found in an isotropic structure, but the lithosphere and asthenosphere exhibit anisotropic structures. For the lithosphere, the main cause of anisotropy is the alignment of anisotropic crystals approximately parallel to the dire

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15

Cheng, Jiubing, Tengfei Wang, Chenlong Wang, and Jianhua Geng. "Azimuth-preserved local angle-domain prestack time migration in isotropic, vertical transversely isotropic and azimuthally anisotropic media." GEOPHYSICS 77, no. 2 (2012): S51—S64. http://dx.doi.org/10.1190/geo2011-0295.1.

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Conventional prestack migration does not preserve local directional information of the seismic waves at the image points. New attempts such as sectored migration of azimuth-limited or common-offset-vector data only concern source-receiver azimuth and offset on the surface, which can be poor representation of subsurface wavepath direction. Moreover, they could result in inaccurate imaging because they do not account for the energy propagation between azimuths or offset-vectors. In the past decade, local angle-domain seismic imaging has been highly advocated to avoid migration artifacts and to i

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16

Rüger, Andreas. "Variation of P-wave reflectivity with offset and azimuth in anisotropic media." GEOPHYSICS 63, no. 3 (1998): 935–47. http://dx.doi.org/10.1190/1.1444405.

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P-wave amplitudes may be sensitive even to relatively weak anisotropy of rock mass. Recent results on symmetry‐plane P-wave reflection coefficients in azimuthally anisotropic media are extended to observations at arbitrary azimuth, large incidence angles, and lower symmetry systems. The approximate P-wave reflection coefficient in transversely isotropic media with a horizontal axis of symmetry (HTI) (typical for a system of parallel vertical cracks embedded in an isotropic matrix) shows that the amplitude versus offset (AVO) gradient varies as a function of the squared cosine of the azimuthal

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17

Cyz, Marta, and Michał Malinowski. "Seismic azimuthal anisotropy study of the Lower Paleozoic shale play in northern Poland." Interpretation 6, no. 3 (2018): SH1—SH12. http://dx.doi.org/10.1190/int-2017-0200.1.

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We have developed a case study of amplitude variation with azimuth (AVAZ) analysis applied to quantify the amount of the azimuthal anisotropy present in the Lower Paleozoic shales of the Baltic Basin (northern Poland). The challenges encountered here are related to thin (up to 25 m) deeply buried (approximately 3 km) targets, characterized by a weak average azimuthal anisotropy (1%–2% from cross-dipole sonic data). Synthetic AVAZ modeling confirms the applicability of the method. We used data after full-azimuth angle-domain prestack depth migration (PSDM) processed by a contractor and in-house

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18

Lynn, Heloise B., David Campagna, K. Michele Simon, and Wallace E. Beckham. "Relationship of P-wave seismic attributes, azimuthal anisotropy, and commercial gas pay in 3-D P-wave multiazimuth data, Rulison Field, Piceance Basin, Colorado." GEOPHYSICS 64, no. 4 (1999): 1293–311. http://dx.doi.org/10.1190/1.1444635.

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This case history is one of three field projects funded by the US Department of Energy as part of its ongoing research effort aimed to expand current levels of drilling and production efficiency in naturally‐fractured tight‐gas reservoirs. The original stated goal for the 3-D P-wave seismic survey was to evaluate and map fracture azimuth and relative fracture density throughout a naturally‐fractured gas reservoir interval. At Rulison field, this interval is the Cretaceous Mesaverde, approximately 2500 ft (760 m) of lenticular sands, silts, and shales. Three‐dimensional full‐azimuth P-wave data

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19

Koren, Zvi, and Igor Ravve. "Azimuthally dependent anisotropic velocity model update." GEOPHYSICS 79, no. 2 (2014): C27—C53. http://dx.doi.org/10.1190/geo2013-0178.1.

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We consider a case where a 3D depth migration has been performed in the local angle domain (LAD) using rich-azimuth seismic data (e.g., conventional land surveys). The subsurface geologic model is characterized by considerable azimuthally anisotropic velocity variations. The background velocity field used for the migration can consist of azimuthally independent, e.g., vertical transverse isotropy, and/or azimuthally dependent (e.g., orthorhombic), velocity layers. The resulting 3D full-azimuth reflection angle gathers generated by the LAD migration represent in situ high-resolution amplitude p

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20

Atmaodi, Berith, and Wahyudi W. Parnadi. "Development of azimuthal resistivity survey data processing program with graphical user interface for anisotropic coefficient quantification." Journal of Physics: Conference Series 2243, no. 1 (2022): 012028. http://dx.doi.org/10.1088/1742-6596/2243/1/012028.

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Abstract The physical properties of underground material are anisotropic. This applies to all physical properties including resistivity. Anisotropic property is quantified by the anisotropic coefficient. The anisotropy of physical properties can be shown by 2D and or 3D modeling, but it is not always economically efficient for small-scale studies, while 1D modeling is not capable of showing the anisotropy effect. One of the many geophysical methods developed to learn about anisotropic properties under the earth is the azimuthal resistivity survey (ARS) which is the improvement of the vertical

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21

Grimm, Robert E., Heloise B. Lynn, C. R. Bates, D. R. Phillips, K. M. Simon, and Wallace E. Beckham. "Detection and analysis of naturally fractured gas reservoirs: Multiazimuth seismic surveys in the Wind River basin, Wyoming." GEOPHYSICS 64, no. 4 (1999): 1277–92. http://dx.doi.org/10.1190/1.1444634.

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Multiazimuth binning of 3-D P-wave reflection data is a relatively simple but robust way of characterizing the spatial distribution of gas‐producing natural fractures. In our survey, data were divided into two volumes by ray azimuth (approximately perpendicular and parallel (±45° to the dominant fracture strike) and separately processed. Azimuthal differences or ratios of attributes provided a rough measure of anisotropy. Improved imaging was also attained in the more coherent fracture‐parallel volume. A neural network using azimuthally dependent velocity, reflectivity, and frequency attribute

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22

Pech, Andrés, and Ilya Tsvankin. "Quartic moveout coefficient for a dipping azimuthally anisotropic layer." GEOPHYSICS 69, no. 3 (2004): 699–707. http://dx.doi.org/10.1190/1.1759456.

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Interpretation and inversion of azimuthally varying nonhyperbolic reflection moveout requires accounting for both velocity anisotropy and subsurface structure. Here, our previously derived exact expression for the quartic moveout coefficient A4 is applied to P‐wave reflections from a dipping interface overlaid by a medium of orthorhombic symmetry. The weak‐anisotropy approximaton for the coefficient A4 in a homogeneous orthorhombic layer is controlled by the anellipticity parameters η(1), η(2), and η(3), which are responsible for time processing of P‐wave data. If the dip plane of the reflecto

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23

Yaskevich, Sergey V., Petr A. Dergach, Gleb S. Chernyshov, Viktor I. Karpukhin, and Anton A. Duchkov. "STUDY OF NEAR-SURFACE ANISOTROPY FOR THE KLUCHI CITE BY REFRACTED WAVES SUTVEYING." Interexpo GEO-Siberia 2, no. 3 (2021): 90–97. http://dx.doi.org/10.33764/2618-981x-2021-2-3-90-97.

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Refracted waves are often used in neat-surface exploration. A limited observation system in the form of unidirectional profiles is often used. In our work, we selected an object with a known anisotropic upper part of the cross-section. The results of refracted waves processing show the anisotropy of one of the layers of the medium, the azimuthal anisotropy of which led to the observation that the refraction on its top ceases from the first arrivals, for the direction of the profile aligned with the axis of symmetry of the azimuthally anisotropic layer.

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24

Tanaka, Satoru. "The Use of Azimuthal Variation in ScS–S Differential Travel Times to Investigate Possible Anisotropy in the Lowermost Mantle Beneath the Philippines." Geosciences 15, no. 2 (2025): 64. https://doi.org/10.3390/geosciences15020064.

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We collected approximately 500 ScS–S differential travel times passing beneath the Philippines with various azimuths to discuss whether there were azimuthal variations in the ScS–S time residuals. By correcting for mantle heterogeneity using a three-dimensional (3D) mantle velocity model, we found a large variance reduction in the ScS–S residuals. In addition, the strong negative correlation between the S and ScS–S time residuals was greatly reduced, while the positive correlation between the ScS and ScS–S time residuals moderately improved, indicating that the corrected ScS–S residuals are ma

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25

Shragge, Jeffrey, and David Lumley. "Elliptical dip moveout for 3D seismic imaging in the presence of azimuthal anisotropy." GEOPHYSICS 77, no. 1 (2012): C1—C12. http://dx.doi.org/10.1190/geo2011-0044.1.

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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 presen

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Grechka, Vladimir, and Sergey Yaskevich. "Azimuthal anisotropy in microseismic monitoring: A Bakken case study." GEOPHYSICS 79, no. 1 (2014): KS1—KS12. http://dx.doi.org/10.1190/geo2013-0211.1.

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Hydraulic fracturing, routinely applied for enhancing the permeability of unconventional oil and gas reservoirs, is one of the possible causes for azimuthal anisotropy of the treated formations. Accounting for both naturally occurring and completion induced azimuthal anisotropy leads to marked improvements in the results of microseismic data processing. As illustrated on a data set acquired in the Bakken Field, North Dakota, USA, those improvements include the possibility of modeling the observed shear-wave splitting, reduction of misfit between the picked and modeled traveltimes of microseism

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Linde, Niklas, and Laust B. Pedersen. "Evidence of electrical anisotropy in limestone formations using the RMT technique." GEOPHYSICS 69, no. 4 (2004): 909–16. http://dx.doi.org/10.1190/1.1778234.

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Azimuthal resistivity surveys are often applied to complement hydrological information or to improve the location of observation boreholes in pump tests. Symmetric electrode configurations cannot distinguish anisotropy from lateral changes or dipping layers, but asymmetric arrays (e.g., the offset Wenner array) can. Tensor radiomagnetotellurics (RMT) is presented as an alternative method in studies of electrical anisotropy in the shallow subsurface. The electromagnetic and geomagnetic transfer functions provide information about the dimensionality of the data. These transfer functions can also

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Tsvankin,, Ilya, and Heloise B. Lynn,. "Special section on azimuthal dependence of P-wave seismic signatures—Introduction." GEOPHYSICS 64, no. 4 (1999): 1139–42. http://dx.doi.org/10.1190/1.1444620.

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This special issue is based on papers presented at the post‐convention SEG workshop on azimuthal dependence of P-wave signatures held in Dallas in 1997. The main motivation for analyzing the azimuthal variation of seismic traveltimes, amplitudes, attenuation, etc. is to obtain reliable information about azimuthal anisotropy in the subsurface. Another potential application of multiazimuth techniques is in finding and mapping desirable lateral heterogeneities that could “masquerade” as azimuthal anisotropy. The last topic has not yet been fully discussed (and is not addressed in the special issu

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Landrø, Martin, and Ilya Tsvankin. "Seismic critical-angle reflectometry: A method to characterize azimuthal anisotropy?" GEOPHYSICS 72, no. 3 (2007): D41—D50. http://dx.doi.org/10.1190/1.2437145.

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Existing anisotropic parameter-estimation algorithms that operate with long-offset data are based on the inversion of either nonhyperbolic moveout or wide-angle amplitude-variation-with-offset (AVO) response. We show that valuable information about anisotropic reservoirs can also be obtained from the critical angle of reflected waves. To explain the behavior of the critical angle, we develop weak-anisotropy approximations for vertical transverse isotropy and then use Tsvankin’s notation to extend them to azimuthally anisotropic models of orthorhombic symmetry. The P-wave critical-angle reflect

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Oh, Ju-Won, and Tariq Alkhalifah. "Optimal full-waveform inversion strategy for marine data in azimuthally rotated elastic orthorhombic media." GEOPHYSICS 83, no. 4 (2018): R307—R320. http://dx.doi.org/10.1190/geo2017-0762.1.

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The orthorhombic (ORT) anisotropic description of earth layers can allow the capture of much of the earth’s anisotropic complexity. The inversion for high-resolution azimuthal variation of anisotropy is important for reservoir characterization, among other applications. A high-resolution description of the azimuth of fractures can help us to predict flow preferences. To verify the feasibility of multiparameter full-waveform inversion (FWI) for marine data assuming azimuthally rotated elastic ORT media, we have analyzed the radiation patterns and gradient directions of ORT parameters to the ref

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Skopintseva, Lyubov, and Tariq Alkhalifah. "An analysis of AVO inversion for postcritical offsets in HTI media." GEOPHYSICS 78, no. 3 (2013): N11—N20. http://dx.doi.org/10.1190/geo2011-0288.1.

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Azimuthal variations of wavefield characteristics, such as traveltime or reflection amplitude, play an important role in the identification of fractured media. A transversely isotropic medium with a horizontal symmetry axis (HTI medium) is the simplest azimuthally anisotropic model typically used to describe one set of vertical fractures. There exist many techniques in industry to recover anisotropic parameters based on moveout equations and linearized reflection coefficients using such a model. However, most of the methods have limitations in defining properties of the fractures due to linear

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Kremor, Joseph, Randall Taylor, and Khalid Amrouch. "Polynomial amplitude versus azimuth inversion in horizontally transverse isotropic media, as tested on fractured coal seams in the Surat Basin." APPEA Journal 57, no. 2 (2017): 776. http://dx.doi.org/10.1071/aj16239.

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A new technique of amplitude versus azimuth (AVAZ) seismic inversion in horizontally transverse isotropic (HTI) media is presented. AVAZ is an effective method of characterising anisotropic variation within individual reflectors as well as characterising fractures. The compressional wave reflectivity equation in HTI media has been reformulated into a parabolic form that allows for fast and efficient inversion. The isotropic component of the azimuthal reflectivity has been separated precisely from the anisotropic component and the anisotropic component has been decoupled exactly into its consti

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Chenin, Bert, and Bob Joyce. "Formation azimuthal anisotropy." Leading Edge 18, no. 2 (1999): 216–20. http://dx.doi.org/10.1190/1.1438256.

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Martins, Jorge L. "Elastic impedance in weakly anisotropic media." GEOPHYSICS 71, no. 3 (2006): D73—D83. http://dx.doi.org/10.1190/1.2195448.

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The original formulation for the P-wave elastic impedance (EI) equation ignores seismic anisotropy. Incorporation of anisotropy effects into the EI formula requires a suitable approximation for reflection coefficients. In order to derive an anisotropic EI equation, this paper uses an approximation for PP-wave reflection [Formula: see text] coefficients which holds for weak-contrast interfaces separating weakly anisotropic media of arbitrary symmetry. Inserting the chosen [Formula: see text] coefficient approximation into the original formalism provides an anisotropic EI formula, which is writt

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Al‐Dajani, AbdulFattah, and Ilya Tsvankin. "Nonhyperbolic reflection moveout for horizontal transverse isotropy." GEOPHYSICS 63, no. 5 (1998): 1738–53. http://dx.doi.org/10.1190/1.1444469.

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The transversely isotropic model with a horizontal axis of symmetry (HTI) has been used extensively in studies of shear‐wave splitting to describe fractured formations with a single system of parallel vertical penny‐shaped cracks. Here, we present an analytic description of longspread reflection moveout in horizontally layered HTI media with arbitrary strength of anisotropy. The hyperbolic moveout equation parameterized by the exact normal‐moveout (NMO) velocity is sufficiently accurate for P-waves on conventional‐length spreads (close to the reflector depth), although the NMO velocity is not,

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Yuan, Sanyi, Jinghan Wang, Tao Liu, Tao Xie, and Shangxu Wang. "6D phase-difference attributes for wide-azimuth seismic data interpretation." GEOPHYSICS 85, no. 6 (2020): IM37—IM49. http://dx.doi.org/10.1190/geo2019-0431.1.

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Phase information of seismic signals is sensitive to subsurface discontinuities. However, 1D phase attributes are not robust when dealing with noisy data. In addition, variations of seismic phase attributes with azimuth are seldom explored. To address these issues, we have developed 6D phase-difference attributes (PDAs) derived from azimuthal phase-frequency spectra. For the seismic volume of a certain azimuth and frequency, we first construct stacked phase traces at each common-depth point along a certain decomposed trending direction. Then, the 6D PDA is extracted by calculating the complex-

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Thomsen, Leon. "Reflection seismology over azimuthally anisotropic media." GEOPHYSICS 53, no. 3 (1988): 304–13. http://dx.doi.org/10.1190/1.1442464.

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Recent surveys have shown that azimuthal anisotropy (due most plausibly to aligned fractures) has an important effect on seismic shear waves. Previous work had discussed these effects on VSP data; the same effects are seen in surface recording of reflections at small to moderate angles of incidence. The anisotropic effects on different polarization components of vertically traveling shear waves permit the recognition and estimation of very small degrees of azimuthal anisotropy (of order ⩾1 percent), as in an interferometer. Anisotropic effects on traveltime yield estimates of anisotropy which

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Sharma, Hema S., Subhashis Mallick, Sumit Verma, and Erin Campbell. "Azimuthal anisotropy analysis of multiazimuth P-wave seismic data — An example from the Rock Springs Uplift, Wyoming, USA." Interpretation 6, no. 3 (2018): T649—T666. http://dx.doi.org/10.1190/int-2017-0230.1.

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Our study area in Rock Sprigs Uplift, Wyoming, lies close to the carbon dioxide ([Formula: see text])-producing Jim Bridger power plant, and hence it is a good site for carbon sequestration. Two subsurface reservoirs within this area are being analyzed for their capability of long-term carbon storage. The presence and orientation of fractures within a reservoir and the associated seal govern the efficiency and long-term effectiveness of [Formula: see text] storage. The presence of natural fractures gives rise to seismic anisotropy that is related to the fracture orientation and density. This w

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Fang, S., A. Merchant, E. Hart, and A. Kirkwood. "Determination of Intrinsic Dip and Azimuth From LWD Azimuthal-Propagation Resistivity Measurements in Anisotropic Formations." SPE Reservoir Evaluation & Engineering 13, no. 04 (2010): 667–78. http://dx.doi.org/10.2118/116123-pa.

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Summary With the use of both azimuthal-propagation-resistivity (APR) and main- and cross-component data, the resistivity anisotropy and its dip and azimuth angles of a massive formation (anisotropic shale or laminated sand) can be determined. The accuracy of the determined parameters depends on the amount of available data. The minimum amount of data required is two frequency main components and real and quadrature cross components. The boundary effects will distort the solution eventually; however, the anisotropy-enhanced processing will minimize the effects to extend the algorithm to a certa

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Watson, Kathryn A., and Ron D. Barker. "Differentiating anisotropy and lateral effects using azimuthal resistivity offset Wenner soundings." GEOPHYSICS 64, no. 3 (1999): 739–45. http://dx.doi.org/10.1190/1.1444583.

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Azimuthal resistivity surveys increasingly are being used by hydrogeologists in the identification and characterization of fractured rocks. In these investigations, electrical resistivity is measured as a function of azimuth about a fixed central point. In most recent published examples, any observed change in apparent resistivity with azimuth is interpreted as being indicative of fracture anisotropy. However, interpretation of rotational sounding data is actually more complicated, as azimuthal variations in apparent resistivity are also produced by the presence of dipping stratigraphy and oth

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Yan, Jia, and Ilya Tsvankin. "AVO-sensitive semblance analysis for wide-azimuth data." GEOPHYSICS 73, no. 2 (2008): U1—U11. http://dx.doi.org/10.1190/1.2834115.

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Conventional semblance-based moveout analysis models prestack reflection data with events that have hyperbolic move-out and no amplitude variation with offset (AVO). Substantial amplitude variation and even phase change with offset do not significantly compromise the semblance operator. However, polarity reversal associated with a change in the sign of the reflection coefficient may cause conventional semblance to fail. An existing modification of the semblance operator that takes amplitude variations into account (so-called AK semblance) is limited to narrow-azimuth data and cannot handle non

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Shragge, Jeffrey. "Elliptical moveout operator for data regularization in azimuthally anisotropic media." GEOPHYSICS 78, no. 1 (2013): C1—C10. http://dx.doi.org/10.1190/geo2012-0227.1.

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Data regularization by azimuthal moveout (AMO) is an important seismic processing step applied to minimize the deleterious effects of irregular and incomplete acquisition in complex geology. Using isotropic AMO operators on data acquired over azimuthally anisotropic media, though, can lead to poor regularization results due to mixing of wavefield information from neighboring traces with azimuthally varying velocity profiles. An elliptical moveout operator (EMO), representing an extension of isotropic AMO to elliptical azimuthally anisotropic media, is sensitive to variations in the magnitude a

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Yao, Zhicheng. "Application of OVT Domain Processing Technology in 3D Seismic Exploration of Coalbed Methane in Heshun Hengling Block." International Journal of Natural Resources and Environmental Studies 3, no. 3 (2024): 55–67. http://dx.doi.org/10.62051/ijnres.v3n3.08.

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This study introduces the OVT (Offset Vector Tile) domain processing technology to improve the accuracy of small structure detection in 3D seismic exploration of coalbed methane in the Heshun-Hengling block in China. The OVT technology optimizes wide azimuth seismic data processing through steps such as facet division, five-dimensional regularization, pre-stack time migration, and azimuthal anisotropy correction. The results show that OVT processing retains azimuth information, enhancing the ability to reflect stratum changes with azimuth; azimuthal anisotropy correction improves the resolutio

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Van De Coevering, Norbert, Klaas Koster, and Rob Holt. "A skeptic's view of VVAz and AVAz." Leading Edge 39, no. 2 (2020): 128–34. http://dx.doi.org/10.1190/tle39020128.1.

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We have applied a modern amplitude- and azimuth-preserving seismic data processing workflow to the SEG Advanced Modeling Program (SEAM) Phase II Barrett classic data set — an orthorhombic synthetic seismic model that has extremely dense sampling of all azimuths and offsets. We analyze the resulting prestack depth-migrated offset vector tiles with a variety of methods and software. Note that we only analyze the P-P wave mode, which is the focus of our study. We demonstrate that observed azimuthal changes cannot be correlated with the model's reservoir properties. We have made the migrated data

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Lynn, Heloise. "Seismic field data displaying azimuthal anisotropy, 1986–2020." Interpretation 8, no. 4 (2020): SP135—SP156. http://dx.doi.org/10.1190/int-2020-0070.1.

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The azimuthal (az’l) processing of 3D full-azimuth full-offset P-P reflection seismic data can enable better imaging, thus yielding improved estimates of structure, lithology, porosity, pore fluids, in situ stress, and aligned porosity that flows fluids (macrofracture porosity). In the past 34 years, the oil and gas industry has significantly advanced in the use of seismic azimuthal anisotropy, in particular, to gain information concerning unequal horizontal stresses and/or vertically aligned fractures, and possibly more importantly, to improve the prestack imaging especially in complex struct

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Gosselin, Jeremy M., Pascal Audet, Andrew J. Schaeffer, Fiona A. Darbyshire, and Clément Estève. "Azimuthal anisotropy in Bayesian surface wave tomography: application to northern Cascadia and Haida Gwaii, British Columbia." Geophysical Journal International 224, no. 3 (2020): 1724–41. http://dx.doi.org/10.1093/gji/ggaa561.

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SUMMARY Surface wave tomography is a valuable tool for constraining azimuthal anisotropy at regional scales. However, sparse and uneven coverage of dispersion measurements make meaningful uncertainty estimation challenging, especially when applying subjective model regularization. This paper considers azimuthal anisotropy constrained by measurements of surface wave dispersion data within a Bayesian trans-dimensional (trans-d) tomographic inversion. A recently proposed alternative model parametrization for trans-d inversion is implemented in order to produce more realistic models than previous

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Leaney, W. Scott, Colin M. Sayers, and Douglas E. Miller. "Analysis of multiazimuthal VSP data for anisotropy and AVO." GEOPHYSICS 64, no. 4 (1999): 1172–80. http://dx.doi.org/10.1190/1.1444624.

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Multioffset vertical seismic profile (VSP) experiments, commonly referred to as walkaways, enable anisotropy to be measured reliably in the field. The results can be fed into modeling programs to study the impact of anisotropy on velocity analysis, migration, and amplitude versus offset (AVO). Properly designed multioffset VSPs can also provide the target AVO response measured under optimum conditions, since the wavelet is recorded just above the reflectors of interest with minimal reflection point dispersal. In this paper, the multioffset VSP technique is extended to include multioffset azimu

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Tang, Xiaoming, and Raghu K. Chunduru. "Simultaneous inversion of formation shear‐wave anisotropy parameters from cross‐dipole acoustic‐array waveform data." GEOPHYSICS 64, no. 5 (1999): 1502–11. http://dx.doi.org/10.1190/1.1444654.

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This study presents an effective technique for obtaining formation azimuthal shear‐wave anisotropy parameters from four‐component dipole acoustic array waveform data. The proposed technique utilizes the splitting of fast and slow principal flexural waves in an anisotropic formation. First, the principal waves are computed from the four‐component data using the dipole source orientation with respect to the fast shear‐wave polarization azimuth. Then, the fast and slow principal waves are compared for all possible receiver combinations in the receiver array to suppress noise effects. This constru

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Downton, Jonathan E., and Benjamin Roure. "Interpreting azimuthal Fourier coefficients for anisotropic and fracture parameters." Interpretation 3, no. 3 (2015): ST9—ST27. http://dx.doi.org/10.1190/int-2014-0235.1.

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Amplitude variation with offset and azimuth (AVOAz) analysis can be separated into two separate parts: amplitude variation with offset (AVO) analysis and amplitude variation with azimuth (AVAz) analysis. Useful information about fractures and anisotropy can be obtained just by examining the AVAz. The AVAz can be described as a sum of sinusoids of different periodicities, each characterized by its magnitude and phase. This sum is mathematically equivalent to a Fourier series, and hence the coefficients describing the AVAz response are azimuthal Fourier coefficients (FCs). This FC parameterizati

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Gajek, Wojciech, Michał Malinowski, and James P. Verdon. "Results of downhole microseismic monitoring at a pilot hydraulic fracturing site in Poland — Part 2: S-wave splitting analysis." Interpretation 6, no. 3 (2018): SH49—SH58. http://dx.doi.org/10.1190/int-2017-0207.1.

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Observations of azimuthal seismic anisotropy provide useful information, notably on stress orientation and the presence of preexisting natural fracture systems, during hydraulic fracturing operations. Seismic anisotropy can be observed through the measurement of S-wave splitting (SWS) on waveforms generated by microseismic events and recorded on downhole geophone arrays. We have developed measurements of azimuthal anisotropy from a Lower Paleozoic shale play in northern Poland. The observed orthorhombic anisotropic symmetry system is dominated by a vertically transverse isotropy (VTI) fabric,

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