Seismic reflection moveout for azimuthally anisotropic media
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002.
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| Format: | Thesis |
| Language: | eng |
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Massachusetts Institute of Technology
2005
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| Online Access: | http://hdl.handle.net/1721.1/8057 |
| _version_ | 1826193054239817728 |
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| author | Al-Dajani, AbdulFattah A |
| author2 | M. Nafi Toksöz. |
| author_facet | M. Nafi Toksöz. Al-Dajani, AbdulFattah A |
| author_sort | Al-Dajani, AbdulFattah A |
| collection | MIT |
| description | Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002. |
| first_indexed | 2024-09-23T09:33:21Z |
| format | Thesis |
| id | mit-1721.1/8057 |
| institution | Massachusetts Institute of Technology |
| language | eng |
| last_indexed | 2024-09-23T09:33:21Z |
| publishDate | 2005 |
| publisher | Massachusetts Institute of Technology |
| record_format | dspace |
| spelling | mit-1721.1/80572019-04-12T22:06:15Z Seismic reflection moveout for azimuthally anisotropic media Al-Dajani, AbdulFattah A M. Nafi Toksöz. Massachusetts Institute of Technology. Dept. of Earth, Atmospheric, and Planetary Sciences. Massachusetts Institute of Technology. Dept. of Earth, Atmospheric, and Planetary Sciences. Earth, Atmospheric, and Planetary Sciences. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002. Includes bibliographical references (p. 281-287). Anisotropy can exist in the subsurface as an intrinsic property, or as an induced property, or as a combination of both. Induced anisotropy can result due to preferred orientation of grains, thin layering, and/or the presence of fractures. In this thesis, we study the reflection moveout for Compressional and Shear waves in horizontally stratified azimuthally anisotropic media. Reflection moveout in common-midpoint (CMP) gathers is generally treated by an azimuthally-isotropic hyperbolic equation. Recently, special treatment for the reflection moveout in azimuthally anisotropic media has been introduced due to the fact that the moveout in such cases is azimuthally dependent. Here, the normal moveout (NMO) equation parameterized by the exact normal-moveout (NMO) velocity is studied. We verify numerically (through synthetic data) the accuracy of the exact (i.e., analytic) azimuthal description of the NMO velocity. We show that the azimuthal variation of the NMO velocity has, in general, a relatively simple elliptical form. We also show that the NMO equation is sufficiently accurate for P- and Shear-wave propagation on conventional spreadlengths (e.g., lenghts close to the reflector depth). The influence of anisotropy causes the deviation of the moveout curve from a hyperbola, even in a homogeneous anisotropic layer with a horizontal interface. Hence, reflection moveout in azimuthally anisotropic media is not only azimuthally dependent but it is also nonhyperbolic. (cont.) To account for the nonhyperbolic moveout, we have derived an exact expression for the azimuthally dependent quartic coefficient of the Taylor series expansion for the two-way traveltimes [t2(x2)] that is valid for any pure mode of wave propagation. As a result, we introduce an analytic representation for the quartic coefficient for pure mode reflection in anisotropic medium with an arbitrary strength of anisotropy. In addition, we present an analytic expression for large-offset, nonhyperbolic reflection moveout (NHMO). Special attention is given in this study toward P-wave propagation in orthorhom-about the same for any strength of anisotropy. To invert for the NMO ellipse parameters at least three NMO-velocity measurements along distinct azimuth directions are needed. In order to maximize the accuracy and stability in parameter estimation, it is best to have the azimuths for the three source-to-receiver directions 60Ê» apart. Having more than three distinct source-to-receiver azimuths (e.g., full azimuthal coverage) enhances the quality of the estimates. The azimuthal variation of the NMO velocity in azimuthally anisotropic media can be utilized to invert for some of the medium parameters which can be useful in characterizing the zone of interest. In HTI media, for example, and using the P-wave reflection moveout, we can estimate three key parameters: the vertical velocity Vpvert, anisotropy parameter 6(V), and the azimuth a of the symmetry-axis ... AbdulFattah Ahmed Al-Dajani. Ph.D. 2005-08-24T19:59:42Z 2005-08-24T19:59:42Z 2002 2002 Thesis http://hdl.handle.net/1721.1/8057 51035875 eng M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. http://dspace.mit.edu/handle/1721.1/7582 287 p. 20356826 bytes 20356580 bytes application/pdf application/pdf application/pdf Massachusetts Institute of Technology |
| spellingShingle | Earth, Atmospheric, and Planetary Sciences. Al-Dajani, AbdulFattah A Seismic reflection moveout for azimuthally anisotropic media |
| title | Seismic reflection moveout for azimuthally anisotropic media |
| title_full | Seismic reflection moveout for azimuthally anisotropic media |
| title_fullStr | Seismic reflection moveout for azimuthally anisotropic media |
| title_full_unstemmed | Seismic reflection moveout for azimuthally anisotropic media |
| title_short | Seismic reflection moveout for azimuthally anisotropic media |
| title_sort | seismic reflection moveout for azimuthally anisotropic media |
| topic | Earth, Atmospheric, and Planetary Sciences. |
| url | http://hdl.handle.net/1721.1/8057 |
| work_keys_str_mv | AT aldajaniabdulfattaha seismicreflectionmoveoutforazimuthallyanisotropicmedia |