The Blackfoot 3C-3D seismic survey: A case study
Gary F. Margrave, Donald C. Lawton, Robert R. Stewart, Susan L. M. Miller, Grace Y. C. Yang, Vladan Simin, Colin C. Potter, Qi Zhang, Todor I. Todorov
A 3C-3D seismic survey was acquired over a Lower Cretaceous incised channel filled with porous cemented sand or possibly shale. Dipole sonic logs reveal the sand-filled channel has an anomalously low VP/VS ratio (or Poisson's ratio) relative to the shale-fill or to regional stratigraphy. Buried (18 m) explosive sources were recorded into a patch of 3C geophones and the data was processed to yield two independent migrated volumes representing P-P and P-S primary reflections. Isochron maps from both volumes were combined algebraically to yield maps of the VP/VS ratio which delineate the channel much better than is possible with P-P data alone. The channel also shows a strong P-P AVO anomaly which is spatially correlated with the VP/VS ratio anomaly.