ANALYSIS OF DIFFRACTIONS IN DIP-ANGLE GATHERS FOR TRANSVERSELY ISOTROPIC MEDIA

摘要

Diffractions can supplement reflected waves in anisotropic velocity analysis because they increase the aperture and may illuminate parts of the model that do not produce strong reflections. However, enhancement of diffractions and their separation from the more intensive reflections remains a challenging task, especially if the velocity model is not accurate. Here, we analyze diffraction events in dip-angle common-image gathers (CIGs) computed with Kirchhoff migration for transversely isotropic (TI) media. If the velocity model is sufficiently accurate, dip-angle CIGs make it possible to generate diffraction-based depth images using a muting function that depends on reflector dip. We demonstrate application of this methodology to anisotropic diffraction imaging of synthetic data and present a field-data example from the Gulf of Mexico. In the presence of errors in the TI parameters, diffraction and reflection events exhibit different moveout distortions in dip-angle CIGs. In particular, numerical examples show that the moveout of diffractions is sensitive to the key anisotropy parameter eta. Therefore, diffractions in the dip-angle domain could be employed in migration velocity analysis (MVA) to refine the anisotropic velocity model.