Correcting for Seabed Canyon Imprint on PSTM Structure and Velocities for Accurate Depth Conversion

When exploring in the emerging abrupt margin play, it is often preferable to interpret in depth rather than time to remove the regional tilt on the seismic data associated with the dipping seabed. Such margins typically contain deeply incised seabed canyons. These canyons create significant push-down effects on time seismic data. In addition to the impact on the time structure, PSTM velocities are also affected, which compounds the push-down when they are used in depth conversion.

A two-method is presented for correcting for seabed canyon effects both on time structure and on seismic velocities, to arrive at an interpretable depth seismic dataset from time-migrated seismic. Firstly the time push-down below the canyons is removed from the seismic, and secondly the velocity imprint of the canyons is removed from the processing velocities before they are used in depth-conversion.

A case study is presented of the method being applied on the Equatorial Margin of Brazil, and compared to the PSDM which arrived a year later. Although the imaging from PSDM is significantly improved, the depth structure and velocity field from this method are shown to be comparable to the final PSDM results.