3-D reverse VSP
Zandong Sun, Robert R. Stewart
3-D reverse VSP is a novel way to create a 3-D image around a borehole. A 3-D numerical modeling experiment with three-component (3-C) receivers is implemented here by raytracing through a model consisting of three layers with a dome on the top of second layer. We find that the converted-wave (P-SV) has wider coverage than P-P wave, and allows us to image more highly dipping reflectors than P-P waves do. The dome in the model with reflector dip angle variation of 0 to 36.9 degrees (dipping away from the borehole) can be 60-70% imaged by the P-SV wave, but can only be imaged 30- 40% by the P-P wave. For a flat interface, 75% of the source-receiver offset from borehole can be imaged by P-SV (Vp/Vs ratio dependent) wave while P-P wave can only image 50%. Practically, for a source-receiver offset of 2500 meters, the P-SV wave can image reflector of dip angle of 30 degrees while P-P wave can only image 20 degrees in both cases that reflector dips away from borehole. We outline an analysis flow for the processing of 3-D reverse vertical seismic profile (RVSP) data. The proposed processing flow includes static removal, several methods of velocity analysis and binning, stacking, and migration.