Interferometric correlogram-space analysis

Seismic interferometry is a method of obtaining a virtual shot gather from a collection of actual shot gathers. The set of traces corresponding to multiple actual shots recorded at two receivers is used to synthesize a virtual shot located at one of the receivers and a virtual receiver at the other. An estimate of a Green’s function between these two receivers is obtained by first cross-correlating pairs of traces from each of the common shots and then stacking the resulting cross-correlograms. In this paper, we study the structure of cross-correlograms obtained from a VSP acquisition geometry using a surface source reflected by flat or dipping layers and/or diffracted by point inclusions. The model is purely acoustic. The shape of events in the cross-correlogram space can be used to infer the location and geometry of a subsurface structure. A pilot wavelet created by a curvilinear stacking process is used as a detector of predicted events in the cross-correlogram. Results of a semblance-based velocity scan of the cross-correlograms using curvilinear stacks can be used to improve the quality of the virtual gather.