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Behaviors of Converted Wave in an Azimuthally Isotropic Medium - A Physical Model Study

Received: 7 August 2019     Accepted: 4 September 2019     Published: 20 September 2019
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Abstract

The existence of subsurface fractures provides not only space for the residence of petroleum but also paths of migration. Therefore, subsurface fractures are of great interest to exploration geophysicists. In reflection seismology, a reservoir of vertically aligned fractures is often considered to possess azimuthal anisotropy, or Horizontal Transverse Isotropy (HTI), in terms of seismic anisotropy. The characteristics and information of this specific type of reservoir are widely obtained using seismic attributes, including the azimuthal variation in the P -wave amplitude and velocity, and the fractional difference of split S-waves. Essentially, a converted (C-) wave is initiated by a downward traveling P-wave, which is converted on reflection to upcoming S-waves. Hence, it combines the behaviors of P- and S-waves in theory. Using a forward model study, this study demonstrates the behaviors of a C-waves in a HTI medium, instead of the behaviors of P- or S-waves. Reflections are facilitated on the horizontal symmetry-axis plane of a scaled HTI model along seven different azimuths using end-on shooting arrangement. Using a P-type transducer as a source and an S-type transducer as a receiver, the behaviors of C-waves in a HTI medium are observed. In the acquired profiles, reflections of P-, PS1- (C1 -), and a mixture of PS2- ( C2-) and S1-waves were detected. The phenomenon of C-wave splitting is also observed because of the behavior of an S-wave in a Transversely Isotropic Medium (TIM), and it could be easily identified in the azimuths near the fracture plane. The reflectivity strengths obtained using a Hilbert transform show that the azimuthal variation in the Amplitude Versus Offset (AVO) for both P- and C1-waves are consistent, but the C1-wave amplitude variation depends more significantly on the azimuth than that of the P-wave. Furthermore, the percentage anisotropy of the C-wave computed from acquired data falls right between those of P- and S-waves. By incorporating C-wave splitting and azimuthal AVO variation into traditional signature analyses, our results show that the fracture orientation is more pronounced when the potential reservoir has vertically aligned fractures.

Published in Earth Sciences (Volume 8, Issue 4)
DOI 10.11648/j.earth.20190804.12
Page(s) 228-234
Creative Commons

This is an Open Access article, distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution and reproduction in any medium or format, provided the original work is properly cited.

Copyright

Copyright © The Author(s), 2019. Published by Science Publishing Group

Keywords

Anisotropy, Converted Wave, Splitting, Amplitude Versus Offset

References
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[18] Gaiser, J. E. and R. Van Dok (2005). Multicomponent processing and fracture characterization analysis of 3-D PS-wave onshore seismic surveys. Society of Petroleum Engineers. https://doi.org/10.2118/93740-MS
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  • APA Style

    Chih-Hsiung Chang, Young-Fo Chang, Hsiu-Chi Tsao. (2019). Behaviors of Converted Wave in an Azimuthally Isotropic Medium - A Physical Model Study. Earth Sciences, 8(4), 228-234. https://doi.org/10.11648/j.earth.20190804.12

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    ACS Style

    Chih-Hsiung Chang; Young-Fo Chang; Hsiu-Chi Tsao. Behaviors of Converted Wave in an Azimuthally Isotropic Medium - A Physical Model Study. Earth Sci. 2019, 8(4), 228-234. doi: 10.11648/j.earth.20190804.12

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    AMA Style

    Chih-Hsiung Chang, Young-Fo Chang, Hsiu-Chi Tsao. Behaviors of Converted Wave in an Azimuthally Isotropic Medium - A Physical Model Study. Earth Sci. 2019;8(4):228-234. doi: 10.11648/j.earth.20190804.12

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  • @article{10.11648/j.earth.20190804.12,
      author = {Chih-Hsiung Chang and Young-Fo Chang and Hsiu-Chi Tsao},
      title = {Behaviors of Converted Wave in an Azimuthally Isotropic Medium - A Physical Model Study},
      journal = {Earth Sciences},
      volume = {8},
      number = {4},
      pages = {228-234},
      doi = {10.11648/j.earth.20190804.12},
      url = {https://doi.org/10.11648/j.earth.20190804.12},
      eprint = {https://article.sciencepublishinggroup.com/pdf/10.11648.j.earth.20190804.12},
      abstract = {The existence of subsurface fractures provides not only space for the residence of petroleum but also paths of migration. Therefore, subsurface fractures are of great interest to exploration geophysicists. In reflection seismology, a reservoir of vertically aligned fractures is often considered to possess azimuthal anisotropy, or Horizontal Transverse Isotropy (HTI), in terms of seismic anisotropy. The characteristics and information of this specific type of reservoir are widely obtained using seismic attributes, including the azimuthal variation in the P -wave amplitude and velocity, and the fractional difference of split S-waves. Essentially, a converted (C-) wave is initiated by a downward traveling P-wave, which is converted on reflection to upcoming S-waves. Hence, it combines the behaviors of P- and S-waves in theory. Using a forward model study, this study demonstrates the behaviors of a C-waves in a HTI medium, instead of the behaviors of P- or S-waves. Reflections are facilitated on the horizontal symmetry-axis plane of a scaled HTI model along seven different azimuths using end-on shooting arrangement. Using a P-type transducer as a source and an S-type transducer as a receiver, the behaviors of C-waves in a HTI medium are observed. In the acquired profiles, reflections of P-, PS1- (C1 -), and a mixture of PS2- ( C2-) and S1-waves were detected. The phenomenon of C-wave splitting is also observed because of the behavior of an S-wave in a Transversely Isotropic Medium (TIM), and it could be easily identified in the azimuths near the fracture plane. The reflectivity strengths obtained using a Hilbert transform show that the azimuthal variation in the Amplitude Versus Offset (AVO) for both P- and C1-waves are consistent, but the C1-wave amplitude variation depends more significantly on the azimuth than that of the P-wave. Furthermore, the percentage anisotropy of the C-wave computed from acquired data falls right between those of P- and S-waves. By incorporating C-wave splitting and azimuthal AVO variation into traditional signature analyses, our results show that the fracture orientation is more pronounced when the potential reservoir has vertically aligned fractures.},
     year = {2019}
    }
    

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  • TY  - JOUR
    T1  - Behaviors of Converted Wave in an Azimuthally Isotropic Medium - A Physical Model Study
    AU  - Chih-Hsiung Chang
    AU  - Young-Fo Chang
    AU  - Hsiu-Chi Tsao
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    PY  - 2019
    N1  - https://doi.org/10.11648/j.earth.20190804.12
    DO  - 10.11648/j.earth.20190804.12
    T2  - Earth Sciences
    JF  - Earth Sciences
    JO  - Earth Sciences
    SP  - 228
    EP  - 234
    PB  - Science Publishing Group
    SN  - 2328-5982
    UR  - https://doi.org/10.11648/j.earth.20190804.12
    AB  - The existence of subsurface fractures provides not only space for the residence of petroleum but also paths of migration. Therefore, subsurface fractures are of great interest to exploration geophysicists. In reflection seismology, a reservoir of vertically aligned fractures is often considered to possess azimuthal anisotropy, or Horizontal Transverse Isotropy (HTI), in terms of seismic anisotropy. The characteristics and information of this specific type of reservoir are widely obtained using seismic attributes, including the azimuthal variation in the P -wave amplitude and velocity, and the fractional difference of split S-waves. Essentially, a converted (C-) wave is initiated by a downward traveling P-wave, which is converted on reflection to upcoming S-waves. Hence, it combines the behaviors of P- and S-waves in theory. Using a forward model study, this study demonstrates the behaviors of a C-waves in a HTI medium, instead of the behaviors of P- or S-waves. Reflections are facilitated on the horizontal symmetry-axis plane of a scaled HTI model along seven different azimuths using end-on shooting arrangement. Using a P-type transducer as a source and an S-type transducer as a receiver, the behaviors of C-waves in a HTI medium are observed. In the acquired profiles, reflections of P-, PS1- (C1 -), and a mixture of PS2- ( C2-) and S1-waves were detected. The phenomenon of C-wave splitting is also observed because of the behavior of an S-wave in a Transversely Isotropic Medium (TIM), and it could be easily identified in the azimuths near the fracture plane. The reflectivity strengths obtained using a Hilbert transform show that the azimuthal variation in the Amplitude Versus Offset (AVO) for both P- and C1-waves are consistent, but the C1-wave amplitude variation depends more significantly on the azimuth than that of the P-wave. Furthermore, the percentage anisotropy of the C-wave computed from acquired data falls right between those of P- and S-waves. By incorporating C-wave splitting and azimuthal AVO variation into traditional signature analyses, our results show that the fracture orientation is more pronounced when the potential reservoir has vertically aligned fractures.
    VL  - 8
    IS  - 4
    ER  - 

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Author Information
  • Department of Biomechatronic Engineering and Research Center for Automation, Chiayi, Taiwan, R. O. C.

  • Institute of Seismology, National Chung Cheng University, Chiayi, Taiwan, R. O. C.

  • Institute of Seismology, National Chung Cheng University, Chiayi, Taiwan, R. O. C.

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