Nonhyperbolic reflection moveout in anisotropic media
- Amoco Production Research, Tulsa, OK (United States)
The standard hyperbolic approximation for reflection moveouts in layered media is accurate only for relatively short spreads, even if the layers are isotropic. Velocity anisotropy may significantly enhance deviations from hyperbolic moveout. Nonhyperbolic analysis in anisotropic media is also important because conventional hyperbolic moveout processing on short spreads is insufficient to recover the true vertical velocity (hence the depth). The authors present analytic and numerical analysis of the combined influence of vertical transverse isotropy and layering on long-spread reflection moveouts. Qualitative description of nonhyperbolic moveout on intermediate spreads (offset-to-depth ratio x/z < 1.7--2) is given in terms of the exact fourth-order Taylor series expansion for P, SV, and P-SV traveltime curves, valid for multilayered transversely isotropic media with arbitrary strength of anisotropy. They use this expansion to provide an analytic explanation for deviations from hyperbolic moveout, such as the strongly nonhyperbolic SV-moveout observed numerically in the case where [delta] > [var epsilon]. With this expansion, they also show that the weak anisotropy approximation becomes inadequate for surprisingly small values of the anisotropies [delta] and [var epsilon]. However, the fourth-order Taylor series rapidly loses numerical accuracy with increasing offset. They suggest a new, more general analytical approximation, and test it against several transversely isotropic models. For P-waves, this moveout equation remains numerically accurate even for substantial anisotropy and large offsets. This approximation provides a fast and effective way to estimate the behavior of long-spread moveouts for layered anisotropic models.
- OSTI ID:
- 6819317
- Journal Information:
- Geophysics; (United States), Journal Name: Geophysics; (United States) Vol. 59:8; ISSN GPYSA7; ISSN 0016-8033
- Country of Publication:
- United States
- Language:
- English
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