Velocity analysis for transversely isotropic media

The conventional long-offset nonhyperbolic moveout equation is derived for the transverse isotropic media with a vertical symmetric axis (VTI). It cannot be extended to the transverse isotropic media with an arbitrary spatial orientation of symmetry axis (ATI). In this paper, we optimize a modifi ed long-offset nonhyperbolic moveout equation for ATI media based on the conventional nonhyperbolic moveout equation and the exact analytical solution of the quartic moveout coeffi cient (A 4 ) and NMO velocity for ATI media that were derived in our previous work. Compared with the exact traveltimes of the ray-tracing algorithm for anisotropic media, this optimized equation can be used to calculate the traveltime varying with survey line azimuth in arbitrary strong or weak ATI media. It can replace the timeconsuming, multi-offset, and multi-azimuth ray tracing method for forward modeling of longoffset refl ection traveltimes in ATI media, which is useful to further anisotropic parameter inversion using long-offset nonhyperbolic moveout.

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Optimized nonhyperbolic moveout correction equation of long-offset seismic data for TI media with an arbitrary spatial orientation

Chen

Zhang³

2010

“…Semblance coefficient velocity analysis (Taner and Koehler, 1969) has always been the standard velocity analysis method and is widely used in converted wave velocity analysis (Thomsen, 1999;Yuan and Li, 2001) and VTI media velocity analysis (Alkhalifah and Tsvankin, 1995;Alkhalifah, 2000;Tsvankin, 1996;You et al, 2006). Up to now, the core algorithms to extract velocity information are all based on the travel time of wavelet's central point.…”

Section: Introductionmentioning

confidence: 99%

Shifted first arrival point travel time NMO inversion

Tan

Han

et al. 2011

Serious stretch appears in shallow long offset signals after NMO correction. In this article we study the generation mechanism of NMO stretch, demonstrate that the conventional travel time equation cannot accurately describe the travel time of the samples within the same refl ection wavelet. As a result, conventional NMO inversion based on the travel time of the wavelet's central point occurs with errors. In this article, a travel time equation for the samples within the same wavelet is reconstructed through our theoretical derivation (the shifted fi rst arrival point travel time equation), a new NMO inversion method based on the wavelet's fi rst arrival point is proposed. While dealing with synthetic data, the semblance coeffi cient algorithm equation is modifi ed so that wavelet fi rst arrival points can be extracted. After that, NMO inversion based on the new velocity analysis is adopted on shot offset records. The precision of the results is signifi cantly improved compared with the traditional method. Finally, the block move NMO correction based on the fi rst arrival points travel times is adopted on long offset records and non-stretched results are achieved, which verify the proposed new equation.

“…The most widely used technique is the third order approximation (Tsvankin and Thomsen, 1994;Alkhalifah and Tsvankin, 1995;Alkhalifah, 1997), which is used mostly in VTI media. Yuan (2001a and2001b) presented a pre-stack time migration algorithm based on the double square root travel time equation.…”

Section: Introductionmentioning

confidence: 99%

Anisotropic converted wave amplitude-preserving prestack time migration by the pseudo-offset method

Zhang

Liu

2008

In this paper, we use the method of pseudo-offset migration (POM) to complete converted wave pre-stack time migration with amplitude-preservation in an anisotropic medium. The method maps the original traces into common conversion scatter point (CCSP) gathers directly by POM, which simplifi es the conventional processing procedure for converted waves. The POM gather fold and SNR are high, which is favorable for velocity analysis and especially suitable for seismic data with low SNR. We used equivalent anisotropic theory to compute anisotropic parameters. Based on the scattering wave traveltime equation in a VTI medium, the POM pseudo-offset migration in anisotropic media was deduced. By amplitude-preserving POM gather mapping, velocity analysis, stack processing, and so on, the anisotropic migration results were acquired. The forward modeling computation and actual data processing demonstrate the validity of converted wave pre-stack time migration with amplitude-preservation using the anisotropic POM method.