Stretch Compensation in Angle Domain - Implication on Wide Angle AVO/AVA Studies

For wide angle datasets there are difficulties in calculating the correct reflection angle values. In addition, wide angle data suffer from imaging stretch effects. In this paper we describe a new approach to compute accurate angle CMP gathers from time migrated offset CMP gathers. The dependencies offset, angle and time are computed through a kinematic pre-stack time de-migration process, taking into account local dips, the effective velocity and anelipticity model. After the kinematic de-migration, we have access to the relationships between the reflection angle and the differential stretch in time of the wavelet for different offsets. A direct (and reverse) angle transform is defined in order to provide accurate seismic traces regularly distributed in angle. Because the amount of stretch is nearly stationary as a function of time in a common angle time-migrated trace, a spectral harmonization along angles can be easily implemented using single spectral reshaping operators. We suggest computing an optimal zero angle wavelet from different angle stacks which minimises errors for all angle spectral shaping operators. The presented stretch compensation impacts on the AVO attribute quality and resolution minimising the low frequency contamination.