In structurally complex environments like the mountains and foothills of the Andes and Rockies, outcropping rocks and differential weathering generate significant seismic-velocity variation in the near surface. In time processing, we correct for these near-surface fluctuations with weathering statics, minimizing the time delays caused by variability in near-surface velocities due to weathering. These statics calculations are made using the first-break energy on shot records—refraction statics—followed by statics that are calculated with the correlation of seismic reflectors—reflection statics. Correcting for near-surface velocity variation with static shifts assumes vertical raypaths through the weathering layer, and this approximation is violated when we have high-velocity rocks outcropping at the surface.
With depth imaging, we have an opportunity to include the refraction velocities from the first breaks in the PSDM velocity model and raytrace through the weathering layers for a more accurate correction for near-surface velocity variation. The refraction solution is only part of the full weathering correction, which is typically followed by a pass of reflection statics. During our testing, we discovered that the reflection statics from the time processing needed to be replaced with depth-domain reflection statics to develop a complete weathering solution for depth imaging. Before calculating reflection statics, we need to correct for the moveout curvature. An offset-moveout correction that is inherently coupled to the PSDM velocity model gives us a complete depth weathering solution (DWS).
See the original article:
https://cseg.ca/a-depth-weathering-solution-for-seismic-imaging/