Enhancing illumination coverage of VSP data by crosscorrelogram migration

A crosscorrelogram migration method is applied to 2-D synthetic data associated with the SEG/EAGE model and to field VSP data from Friendswood, Texas. The remarkable feature in this method is that both the source positions in the RVSP data or the drill-bit or the receiver positions in the VSP data and the pilot signals do not need to be known. The crosscorrelation method is first applied to synthetic data from the SEG/EAGE salt model. Test results show an accurate reflectivity image obtained by migrating crosscorrelated seismic-data traces generated by a source moving along a drilling hole, even in the presence of severe static shift errors. The resulting migration images from the field data are compared with well data adjacent to the well rig. The results show that the crosscorrelogram migration image correlates reasonably well with the well log. In addition, examples from both synthetic and field data demonstrate that this new migration method extends the illumination coverage beyond that of the standard migration method. It can be used for VSP, RVSP, and drill-bit passive seismic imaging when we have little information about the source position and the pilot signal.