Migração (2,5-D) com amplitudes verdadeiras em meios com gradiente constante de velocidade

Abstract

The true-amplitude seismic migration, in time or depth, provides a measurement of the reflection coefficients of primary reflection events. These are constituted by P-P reflection of longitudinal waves at smooth reflectors. One of the mostly used method is the Kirchhoff migration, by which the seismic image is obtained by stacking the seismic wavefield using a diffraction surface, also called Huygens Surface. In order to obtain true amplitude migration, i.e. the removal of geometrical spreading, it is introduced a weight function in the migration operator. The weight function is determined by the asymptotic solution of the migration integral at stationary points. The ray tracing is a fundamental tool for determining the weight function and the traveltime, that increases the computational costs of the migration process in heterogeneous media. In this work it is presented a true-amplitude migration algorithm tailored for two-and-one-half dimensional model, i.e. when the velocity field varies only with two coordinates of the three dimensional Cartesian system. It is emphasized the special case of constant gradient velocity. As a second topic, this work concerns about recovering seismic attributes from pre-stack seismic data by applying the double diffraction stack inversion. The estimated parameter is the incidence angle at the reflector. Combining the estimated reflection coefficient and the incidence angle, it is possible to perform the so-called Amplitude versus Angle Analysis (AVA) on the interested reflector.