Anisotropic semblance analysis and NMO corrections for long offset data

Fanmin Zhang; Norm Uren

doi:10.1071/ASEG2003ab188

ISSN: 2202-0586
E-ISSN:

oa Anisotropic semblance analysis and NMO corrections for long offset data
Authors Fanmin Zhang^a and Norm Uren^b
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^a Dept. of Exploration GeophysicsCurtin University of Technology, GPO Box U1987 WA, 6845, [email protected] ^b Dept. of Exploration GeophysicsCurtin University of Technology, GPO Box U1987 WA, 6845, [email protected]
Publisher: Australian Society of Exploration Geophysicists
Source: ASEG Extended Abstracts, Volume 2003, Issue ASEG2003 - 16th Geophysical Conference, Aug 2003, p. 1 - 5
DOI: https://doi.org/10.1071/ASEG2003ab188
- Published online: 01 Aug 2003

Abstract

Sedimentary rocks can be regarded as transversely isotropic (TI) media. One difficulty in seismic processing is how to flatten the events for long offset data. P-wave reflections from horizontal reflectors in transversely isotropic media have non-hyperbolic moveout. For a multi-layered model, the reflection moveout formula is usually expressed as a Taylor series with higher order terms ignored. Alkhalifah and Tsvankin (1995) developed a three term Taylor series formula to calculate reflection travel times from a horizontal reflector in TI media with vertical symmetry axis (VTI). Using this formula, NMO correction works well for short spread lengths, but not so well for long spreads.

Zhang and Uren (2001 a, b) developed an approximate explicit analytical P-wave ray velocity function for transversely isotropic (TI) media. From this ray velocity function, a reflection travel time formula from a horizontal reflector in TI media was derived. This formula can be used for anisotropic NMO correction. It works well for both large offsets and small offsets. In order to obtain the unknown parameters required for seismic processing, a 3D-semblance analysis technique has been developed. We tested this method with numerical data from TI models with a single horizontal reflector and from multi-horizontal reflector models. The method was also tested with an isotropic model with multi-horizontal reflectors. The results show that the events can be completely flattened even for very large offsets and that both multi-layered TI and isotropic models may appear to be anisotropic.

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References

Alkhalifah, T. and Tsvankin, I., 1995, Velocity analysis for transversely isotropic media: Geophysics, 60, 1550-1566.
Alkhalifah, T., 1997, Velocity analysis using nonhyperbolic moveout in transversely isotropic media: Geophysics, 62, 1839-1854.
Babuska, V., and Cara, M., 1991, Seismic anisotropy in the earth: Kluwer Academic, the Netherlands.
Fedorov, F. I., 1968, The theory of elastic waves in crystals: Plenum Press, New York.
Hake, H., Helbig, K., and Mesdag, C. S., 1984, Three-term Taylor series for f2-*2 curves over layered transversely isotropic ground: Geophys. Prosp., 32, 828-850.
Larner, K., 1993, Dip-moveout error in transversely isotropic media with linear velocity variation in depth: Geophysics, 58, 1442-1453.
Levin, F. K., 1971, Apparent velocity from dipping interface reflections: Geophysics, 36, 510-516.
Levin, F. K., 1979, Seismic velocities in transversely isotropic media: Geophysics, 44, 918-936.
Levin, F. K., 1980, Velocities for transversely isotropic media, II: Geophysics, 45, 3-17.
Thomsen, L. A., 1986, Weak elastic anisotropy: Geophysics, 51, 1954-1966.
Tsvankin, I., 1996, P-wave signitures and notation for transversely isotropic media: An overview: Geophysics, 61, 467-483.
Tsvankin, I., and Thomsen, L., 1994, Nonhyperbolic reflection moveout in anisotropic media: Geophysics, 59, 1290-1304.
Uren, N. F., Gardner, G. H. F., and McDonald, J. A., 1990, The migrator’s equation for anisotropic media: Geophysics, 55, 1429-1434.
Zhang F. and Uren N., 2001 (a), Explicit anisotropic P-wave velocity functions: 15th ASEG conference, Brisbane, Australia (CD).
Zhang F. and Uren N., 2001 (b), Approximate explicit ray velocity functions and travel times for P-waves in TI media: 71st Ann. Internat. Mtg., Soc. Explor. Geophys., Expanded Abstracts, Vol I, 106-109.
Zhang F. and Uren N., 2002, P-wave ray velocity functions, semblance analysis and NMO corrections in transversely isotropic media: 72nd Ann. Internat. Mtg., Soc. Explor. Geophys., Expanded Abstracts, Vol I, 133-136.

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Article Type: Research Article

Keyword(s): NMO corrections; ray velocity functions; semblance analysis; TI media; travel times

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oa Anisotropic semblance analysis and NMO corrections for long offset data

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