The use of common scatter point gathers to detect amplitude variation with offset

Shuang Sun

The use of common scatterpoint (CSP) gathers for amplitude variation with offset analysis is investigated. Both the migration aperture and the scaling factor used during CSP gathering are considered. The Fresnel zone concept was expanded for an offset section and then generalized to the prestack data volume, to define the minimum migration aperture. A migration aperture larger than this size had no improvement on the migration amplitude.

Three methods are presented that use limited aperture and different weighting schemes when forming the CSP gathers. The first method uses an aperture that is half the size of the Fresnel zone along with a fold balancing scheme that is based on the sample fold. The second method uses the full size of the Fresnel zone and scaling with the equivalent wavenumber migration (EWM) weighting function. The third method also uses the full size of the Fresnel zone but with an exponential scaling factor. The three methods are applied both to synthetic and field data. The results verify that the first and third approximations provide reliable amplitudes in the CSP gather that can be used for amplitude variation with offset (AVO) analysis.