ABSTRACT

For vertical-seismic-profiling (VSP) measurements, the use of blended acquisition, with time-overlapping shot records, can greatly reduce the downtime and, thereby, provide large cost savings. For directly imaging blended VSP measurements, we have used full-wavefield migration (FWM). FWM is an inversion-based imaging scheme that enables us to use any kind of complex source wavefield to estimate the subsurface reflectivity, using all the multiples (surface and internal) in the recorded data. The multiple scattering helps in improving the illumination as well as the vertical resolution of the image. In this scheme, active deblending is not required because the imaging process itself acts as a deblending procedure. We tested the potential of FWM to image blended VSP data, using simple and complex synthetic models. We clearly determined that using the primaries, surface multiples, and internal multiples enhanced the illumination away from the well trajectory, in which blending noise was suppressed due to the inversion scheme. We observed that some blending crosstalk noise leaked into the images with large blending factors. Such noise could be further reduced with additional constraints in the involved least-squares inversion process.

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