Abstract: Equalizing Stacking Velocities of Dipping Events

John W. Sherwood, Philip Schultz, David Judson

It is well known that a steeply dipping primary reflection requires a higher CDP stacking velocity than a time-coincident flat-dip primary reflection. Thus, important steep-dip seismic events, such as fault-plane reflections and the limbs of diffraction patterns, that may be present in the pre-stack data typically are rejected from a conventional CDP stack section.

In an attempt to remedy this situation Digicon has implemented DEVILISH, a novel procedure which can be applied to uniformly recorded seismic data prior to CDP stack. From an interpreted and approximate flat-dip stacking velocity function, which may change slowly along the assumed dip line, DEVILISH designs time-varying, multi-CDP filters for application to the prestack data. These filters have the property of leaving a zero-offset section completely unaltered. For nonzero offsets there is no change of flat-dip events, but steep-dip events are given the approximate theoretical spacetime adjustment that will lead to their optimal stack using the flat-dip velocity function. The resulting CDP stack should then display those steep-dip primary reflections which were sampled adequately in t e basic seismic data and which conform to the inherent assumptions and approximations mentioned.

Departures from the ideal clearly will result in a suboptimum stack section, but in all realistic situations the DEVILISH stack section should be significantly closer to optimality than the conventional stack.

AAPG Search and Discovery Article #90963©1978 AAPG/SEG/SEPM Pacific Section Meeting, Sacramento, California