Frequency‐wavenumber constant‐offset migration and AVO analysis

Abstract

Low signal to noise ratios, interfering diffractions, and dip related problems make reliable amplitude versus offset (AVO) analysis a difficult task. Prestack time migration collapses diffractions, increases the S/N ratio, and reduces dip related problems. Performing prestack time migration before AVO is therefore often required before offset dependent information can be extracted from seismic data. A two-dimensional (2-D) frequency-wavenumber common-offset prestack time migration algorithm is given. In order to treat the amplitudes correctly, a 3-D to 2-D transform of the data is required before the migration. This is done by correcting the data for the out-of-plane geometrical spreading. Migration artifacts are attenuated by using a migration aperture which decreases with increasing traveltime and offset. The final processing steps before AVO analysis are 2-D geometrical spreading correction and removal of the implicit NMO correction inherent in the migration. Applied to a marine data set, the prestack algorithm gives encouraging results in context of AVO analysis. After prestack time migration an AVO anomaly is revealed which not is present in the unmigrated data, and several AVO artifacts have disappeared.