3D TRUE-AMPLITUDE PRESTACK DEPTH MIGRATION

摘要

The angle-dependent reflectivity of a reservoir target is crucial input for reservoir characterization. 3D prestack depth migration should be able to produce not only an accurate structural image, but also reliable angle-dependent amplitude information. However, none of the currently available 3D migration algorithms satisfy this requirement. Geometrical spreading is the only consideration in most existing true-amplitude migrations; intrinsic attenuation, and transmission losses also distort the wavefield amplitudes during propagation through the earth. We develop an integrated algorithm that compensates all three of these factors, in a two-pass recursive reverse-time 3D prestack depth migration. Applications to 3D synthetic models demonstrate production of both high quality subsurface images and angle-dependent (prestack) reflection coefficients at the target. The velocity ratio at the target is also obtained by least square fitting over the estimated angle-dependent reflection coefficients. Because of the nature of reverse-time migration and the recursive procedure, the 3D algorithm is computationally and memory intensive. However, for application to real seismic data, 3D true amplitude processing is necessary.