P - 366 Removing NMO/Migration Stretch Effects for Improved AVO Analysis Anat Canning and Alex Malkin, Paradigm Ltd. Summary An un-stretching algorithm in reflection angle domain is presented and demonstrated with examples. It shows excellent results and improved AVO analysis. Introduction The effect of NMO/migration stretch has recently become an important topic of discussion in the context of AVO analysis (Swan, 1997, Castoro, White, and Thomas, 2001, Figure 1: Offset gather – created by common offset migration of synthetic data. and Hicks, 2002, Perez and Marfurt 2006). NMO/migration stretch causes wavelet distortions as a function of offset, which then creates a significant error in measuring AVO gradients, and significantly distorts amplitude inversion and seismic reservoir characterization procedures. Figure 1 displays an offset gather created by common offset Kirchhoff prestack migration. Input to migration was a synthetic dataset that was composed of four horizontal interfaces with constant reflectivity at all offsets. Note that stretch at far offsets is mostly evident at shallow layers where angle of incidences are large. Note also that the stretch varies with time at a given offset. Figure 2 focuses on the top reflection which is highly stretched and illustrates the effect of the stretch in creating false AVO anomalies. a)Offset gather, red line marks the location of the AVO response which is presented in b. b) AVO signature for the trough marked red in a. Note that input for migration was data with constant amplitude with offset. Still, the measured AVO has a sharp decay with offset which is false and is caused by the stretch. Figure 2:False AVO response due to stretch.