Reflection tomography in the migrated domain can help reconstruct heterogeneous, anisotropic velocity fields needed for accurate depth imaging of complex geologic structures. The presence of anisotropy, however, increases the uncertainty in velocity analysis and typically requires a priori constraints on the model parameters. Here, we develop a 2D P-wave tomographic algorithm for heterogeneous transversely isotropic media with a tilted symmetry axis (TTI) and investigate the conditions necessary for stable estimation of the symmetry-direction velocity [Formula: see text] and the anisotropy parameters [Formula: see text] and [Formula: see text]. The model is divided into rectangular cells, and the parameters [Formula: see text], [Formula: see text], [Formula: see text], and the tilt [Formula: see text] of the symmetry axis are defined at the grid points. To increase the stability of the inversion, the symmetry axis is set orthogonal to the imaged reflectors, with the tilt interpolated inside each layer. The iterative migration velocity analysis involves efficient linearized parameter updating designed to minimize the residual moveout in image gathers for all available reflection events. The moveout equation in the depth-migrated domain includes a nonhyperbolic term that describes long-offset data, which are particularly sensitive to [Formula: see text]. Synthetic tests for models with a “quasi-factorized” TTI syncline (i.e., [Formula: see text] and [Formula: see text] are constant inside the anisotropic layer) and a TTI thrust sheet demonstrate that stable parameter estimation requires either strong smoothness constraints or additional information from walkaway VSP (vertical seismic profiling) traveltimes. If the model is quasi-factorized with a linear spatial variation of [Formula: see text], it may be possible to obtain the interval TTI parameters just from long-spread reflection data.
|Original language||English (US)|
|Number of pages||1|
|State||Published - 2013|
Bibliographical noteKAUST Repository Item: Exported on 2021-09-21
Acknowledgements: We are grateful to CWP alumni Debashish Sarkar (GXT), Zhenyue Liu (ExxonMobil), and Tariq Alkhalifah (KAUST, Saudi Arabia) for significant contributions to Seismic Unix, which serves as the platform for our software development. We also thank Sam Gray (CGGVeritas) for providing the data for the second synthetic example, and Mirko van der Baan, Sam Gray, Ivan Pšenčík, and two anonymous referees for their reviews of the manuscript. X. Wang would like to thank Zhaobo Meng (In-Depth Geo) for his help and advice during an internship with ConocoPhillips in 2009. This work was supported by the Consortium Project on Seismic Inverse Methods for Complex Structures at the Center for Wave Phenomena.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.