The Blackfoot 3C-3D seismic survey: A case study

Gary F. Margrave, Don C. Lawton, Robert R. Stewart, Susan L.M. Miller, Grace Y.C. Yang, Vladan Simin, Colin C. Potter, Qi Zhang and Todor 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 V P /V S 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 V P /V S 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 V P /V S ratio anomaly.

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