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CWP-687 Migration velocity analysis for TI media with quadratic lateral velocity variation

By Mamoru Takanashi and Ilya Tsvankin

Abstract

One of the most serious problems in anisotropic velocity analysis is the tradeoff between anisotropy and lateral heterogeneity, especially if velocity varies on a scale smaller than spreadlength. Here, we develop a P-wave MVA (migration velocity analysis) algorithm for transversely isotropic (TI) models that include layers with small-scale lateral heterogeneity. Each layer is described by constant Thomsen’s parameters ɛ and δ and the symmetry-direction velocity V0 that varies as a quadratic function of the distance along the layer boundaries. For tilted TI media (TTI), the symmetry axis is taken orthogonal to the reflectors. We analyze the influence of lateral heterogeneity on image gathers obtained after prestack depth migration and show that quadratic lateral velocity variation in the overburden can significantly distort the moveout of the target reflection. If such errors are not corrected, the medium parameters beneath the heterogeneous layer(s) are estimated with significant error, even when borehole information (e.g., check shots or sonic logs) is available. Since the residual moveout is highly sensitive to lateral heterogeneity in the overburden, our algorithm simultaneously inverts for the parameters of all layers or blocks. Synthetic tests demonstrate that if the vertical profile of the symmetrydirection velocity V0 is known at one location, the algorithm can reconstruct the other relevant parameters throughout the medium. The developed method should increase the robustness of anisotropic velocity model-building and image quality in the presence of laterally heterogeneous layers in the overburden. Key words: medi

Topics: MVA, VTI, TTI, quadratic lateral velocity variation, factorized
Year: 2014
OAI identifier: oai:CiteSeerX.psu:10.1.1.418.3122
Provided by: CiteSeerX
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