Tangent-Phase Interferometry, Time Lapse Application and Sensitivity Analysis

Seismic interferometry by crosscorrelation is a known representation method used in seismic exploration to reconstruct the Green's function between receivers and to remove the overburden effects when buried receivers are used to record the seismic signals. An issue in conventional seismic interferometry applications for exploration purposes may be the lack of illumination coverage by real sources with a given receiver geometry for natural, i.e., data-based, Kirchhoff-Helmholtz representation of crosscorrelation type for the propagating wavefields. This shortcoming may be overcome by modified representation based on tangent analysis for selected events, and using partial model knowledge to locate new projected points where to calculate virtual signals. This interferometry method uses a generalized-phase operator in a modified representation integral. We investigate the sensitivity of the generalized phase interferometry (GPI) method to velocity variation, and the use of this approach for time-lapse purposes. We present crosswell examples where the acquisition geometry has no complete coverage for the illumination of a buried velocity lens by conventional seismic interferometry application. The results show that the GPI provides a set of new seismogram gathers for each couple of receivers, sensitive to time-lapse variations.