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sep:research:theses:sep154 [2014/08/07 21:45]
myfusan created
sep:research:theses:sep154 [2015/05/27 02:06] (current)
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  * Appendix B: [[http://sepwww.stanford.edu/data/media/public/docs/sep154/append2.pdf|Rock physics modeling]]   * Appendix B: [[http://sepwww.stanford.edu/data/media/public/docs/sep154/append2.pdf|Rock physics modeling]]
  * Appendix C: [[http://sepwww.stanford.edu/data/media/public/docs/sep154/append3.pdf|RTM-based WEMVA for VTI models]]   * Appendix C: [[http://sepwww.stanford.edu/data/media/public/docs/sep154/append3.pdf|RTM-based WEMVA for VTI models]]
 +  * [[http://sepwww.stanford.edu/data/media/public/docs/sep154/bibli.pdf|Bibliography]]\\
 +
 +
**Abstract** **Abstract**
 +
Wave-equation migration velocity analysis (WEMVA) is a powerful technique for robust velocity model building when the subsurface is complex and the starting model is far from true. However, this traditional isotropic WEMVA technique cannot explain anisotropic wave phenomenon, which has significant effects when the reflectors are steeply dipping and/or the waves are traveling at large angles. Furthermore, errors in Wave-equation migration velocity analysis (WEMVA) is a powerful technique for robust velocity model building when the subsurface is complex and the starting model is far from true. However, this traditional isotropic WEMVA technique cannot explain anisotropic wave phenomenon, which has significant effects when the reflectors are steeply dipping and/or the waves are traveling at large angles. Furthermore, errors in
the anisotropic parameters cause similar defocusing as errors in isotropic velocity. Any defocusing caused by anisotropy may be translated to false updates in the isotropic velocity, which lead to further mispositioning and misinterpretations. However, simple extension of the isotropic WEMVA to the anisotropic medium cannot provide an unique and reliable solution due to the nonlinear and underdetermined nature of the anisotropic model building problem. Many anisotropic models with vastly different geological interpretations may explain the surface seismic data equally well. the anisotropic parameters cause similar defocusing as errors in isotropic velocity. Any defocusing caused by anisotropy may be translated to false updates in the isotropic velocity, which lead to further mispositioning and misinterpretations. However, simple extension of the isotropic WEMVA to the anisotropic medium cannot provide an unique and reliable solution due to the nonlinear and underdetermined nature of the anisotropic model building problem. Many anisotropic models with vastly different geological interpretations may explain the surface seismic data equally well.
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2-D examples show that the anisotropic WEMVA technique can resolve the errors in 2-D examples show that the anisotropic WEMVA technique can resolve the errors in
both velocity and anisotropic parameters. Consequently, the migration images are both velocity and anisotropic parameters. Consequently, the migration images are
 +improved with higher resolution and correct depths for the reflectors.
 +
 +
 +Second, I mitigate the ambiguities among the anisotropic parameters using the
 +rock physics prior information. I model shale anisotropy in the seismic scale from well
 +log measurements and the interpretation results from a previous isotropic processing
 +workflow . By varying the key parameters to the rock physics models, I include different
 +geological scenarios and parameter uncertainties in the rock physics modeling.
 +As a result, multiple realizations of the anisotropic parameters are obtained and used
 +as the rock physics constraints for the seismic data inversion. On a synthetic example,
 +I show the correct rock physics regularization accelerates the convergence of the
 +well constrained parameter and brings extra information for the poorly constrained
 +parameters. Anisotropic WEMVA inversion of a 3-D field data set yields models that
 +are consistent with seismic data, geological knowledge, as well as rock physics information.
 +The migration image based on the inverted models shows better-resolved
 +faulting discontinuities and better imaged salt flanks.
 +
 +**Reproducibility and source codes**\\
 +This thesis has been tested for [[sep:research:reproducible|reproducibility]]. The source codes are made available for [[http://sepwww.stanford.edu/data/media/private/docs/sep154/src.tgz|download]]. The scripts are available for [[http://sepwww.stanford.edu/data/media/private/docs/sep154/chap3.tgz|chapter 3]] and
 +[[http://sepwww.stanford.edu/data/media/private/docs/sep154/chap4.tgz|chapter 4]].\\
 +
 +**Defense**\\
 +[[http://sepwww.stanford.edu/data/media/public/docs/sep154/elita-defense.pptx|Defense presentation]]\\
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