Underground imaging of seismic events by generation of composite surface wavefields which are stacked to produce prestack migration

摘要

A prestack migration method allowing imaging of an underground zone, for a given velocity model of arbitrary complexity. By means of conventional wave propagation and retropropagation modelling tools, the method allows to obtain elementary migrated images associated with the values assumed by a parameter and the sum of the images obtained for the different values of the parameter (post-migration stacking), in the depth domain as well as in the time domain. This migration is obtained at an attractive price (calculation cost) because it is independent of the volume of the results calculated and of the number of seismic traces recorded. Only the volume of the zone in which the waves are propagated, the complexity of the events to be imaged and the desired accuracy have an effect on the calculation cost. Volume images are thus obtained by taking account of all the seismic traces. It is thus possible to implement a plane wave migration procedure in cases where acquisition does not allow synthesis of the subsurface response to a plane wave excitation, a response required from the outset in conventional plane wave migration algorithms. The method can be applied for imaging of geologic interfaces or heterogeneities of a part of an underground zone.