Converted-wave seismology in anisotropic media revisited, Part I: Basic theory

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.

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“…In VTI media, converted wave travel times must satisfy the non-hyperbolic equation (Li and Yuan, 2005a;2005b):…”

Section: Travel Time Equation Of Converted Waves In Vti Mediamentioning

confidence: 99%

“…The anisotropic equations are given as follows. The scattering travel time equation at (x, z) in VTI media Yuan, 2005a and2005b;Ma and Tang, 2007) is:…”

Section: Travel Time Equation Of Converted Waves In Vti Mediamentioning

confidence: 99%

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

Zhang

Liu

2008

Appl. Geophys.

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“…According to the parameter definition of Thomsen (1999), by introducing a factor χ eff that represents the anisotropic effect of PS-wave in VTI media, derived a four-parameter (stacking velocity V C2 , vertical velocity ratio γ 0 , effective velocity ratio γ eff , and anisotropic parameter χ eff ) time-distance curve equation for simplifi ed multilayered VTI media; furthermore, they extended the PS-wave prestack time migration double square root scattering wave equation from a single layer to multiple layers in VTI media and presented the relation between the initial velocity model of the PS-wave prestack time migration and the four-parameter stacking velocity model. Li and Yuan (2003, 2005a, 2005b further studied the conversion point calculation and traveling time four-parameter model, developed a PSwave PKTM imaging approach based on the asymptotic conversion point four-parameter velocity model, and provided a scheme and examples of the four-parameter velocity analysis. To improve the anisotropic parameters' reliability of the four-parameter velocity analysis, Miao and Zuk (2006) presented the simultaneous estimation of P-wave and PS-wave anisotropic parameters.…”

Section: Introductionmentioning

confidence: 99%

Prestack migration velocity analysis based on simplified two-parameter moveout equation

Chen

Qian

et al. 2016

Appl. Geophys.

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Stacking velocity V C2 , vertical velocity ratio γ 0 , effective velocity ratio γ eff , and anisotropic parameter χ eff are correlated in the PS-converted-wave (PS-wave) anisotropic prestack Kirchhoff time migration (PKTM) velocity model and are thus difficult to independently determine. We extended the simplified two-parameter (stacking velocity V C2 and anisotropic parameter k eff ) moveout equation from stacking velocity analysis to PKTM velocity model updating and formed a new four-parameter (stacking velocity V C2 , vertical velocity ratio γ 0 , effective velocity ratio γ eff , and anisotropic parameter k eff ) PS-wave anisotropic PKTM velocity model updating and process fl ow based on the simplifi ed twoparameter moveout equation. In the proposed method, first, the PS-wave two-parameter stacking velocity is analyzed to obtain the anisotropic PKTM initial velocity and anisotropic parameters; then, the velocity and anisotropic parameters are corrected by analyzing the residual moveout on common imaging point gathers after prestack time migration. The vertical velocity ratio γ 0 of the prestack time migration velocity model is obtained with an appropriate method utilizing the P-and PS-wave stacked sections after level calibration. The initial effective velocity ratio γ eff is calculated using the Thomsen (1999) equation in combination with the P-wave velocity analysis; ultimately, the final velocity model of the effective velocity ratio γ eff is obtained by percentage scanning migration. This method simplifi es the PS-wave parameter estimation in high-quality imaging, reduces the uncertainty of multiparameter estimations, and obtains good imaging results in practice.

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Seismic inversion and fracture prediction in tilted transversely isotropic media

Wang

Yang

et al. 2022

Journal of Geophysics and Engineering

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The conventional Amplitude variation with offset (AVO) inversion has been mainly developed for the isotropic media and therefore it is generally inapplicable to the anisotropic fractured formations. A set of tilted fractures in isotropic medium can be regarded as a transversely isotropic (TTI) medium. The reflection coefficient equation in TTI media contains many parameters such as anisotropic parameters, velocities, azimuth and dip angles. The selection of objective functions can significantly affect its performance in searching for the optimal solution. The seismic inversion of the TTI medium remains challenging because of its many parameters, and is very complicated after conversion into solving function problems. The genetic algorithm (GA) provides a universal framework to solve the optimization problem in complex systems, and it is independent of the types and disciplines of problems. In this study, the GA-based seismic prestack inversion of the TTI medium is implemented by constructing the objective functions of anisotropic parameters based on the TTI medium reflection coefficient approximation. The inversion performance is shown to be satisfactory on the one-dimensional well logging model, modified Hess model and the field datum. Furthermore, fracture filling materials are well predicted according to the theories of the equivalent medium for fractured materials and fracture weakness. The inversion results demonstrate the proposed method to be feasible and robust. The findings of this research are expected to provide theoretical guidance for the inversion of elastic parameters of anisotropic media and fracture type identification in hydrocarbon reservoirs.

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Converted-wave seismology in anisotropic media revisited, Part I: Basic theory

Cited by 5 publications

References 12 publications

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

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

Prestack migration velocity analysis based on simplified two-parameter moveout equation

Seismic inversion and fracture prediction in tilted transversely isotropic media

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