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A B S T R A C TWe use different interferometry approaches to process the seismic signals generated by a drill-bit source in one well and recorded by seismic receivers located both in a second borehole and at the surface near the source well. We compare the standard interferometry results, obtained by using the raw drill-bit data without a pilot signal, with the new interferometry results obtained by using the drill-bit seismograms correlated with a reference pilot signal. The analysis of the stationary phase shows that the final results have different S/N levels and are affected by the coherent noise in the form of rig arrivals. The interferometry methods are compared by using different deconvolution approaches. The analysis shows that the results agree with the conventional drill-bit seismograms and that using the reference pilot signal improves the quality of the drill-bit wavefields redatumed by the interferometry method.

Drill‐bit seismic while drilling provides reverse vertical seismic profiles with large configurations of surface seismic sensors. This seismic while drilling technique makes it possible to predict the formation changes ahead of the bit and to image 2D and 3D structures without interfering with the drilling activity. The method is based on the recording of reference (pilot) signals which enable us to recognize and process the signal of the downhole drill‐bit source, thus obtaining impulsive seismograms after the crosscorrelation and deconvolution of the pilot signals and the seismic data recorded by surface or crosswell geophones. One issue in the application of this methodology can be the loss of the transmitted energy for the reference signal propagated from the bit to the surface through the drill string, when the pilot signals are recorded at the surface, at the top of the drill string. It is well known that with polycrystalline diamond compact bits, the pilot signal recorded at the surface may be weak and consequently the seismic while drilling results are poor. This may also happen during drilling in the sliding mode without pipe rotation, and in highly deviated or horizontal wells. A solution to improve the drill‐bit seismic while drilling method in these conditions is to record the reference signal in the proximity of the bit source, using downhole near‐bit tools to get good‐quality measurements of the pilot signal. We present drill‐bit seismic while drilling results obtained in a drilling test using wired pipes for high‐rate communication from bottom hole to the surface. The results demonstrate the applicability of this integrated approach as a standard procedure. The advantage of this is to provide real‐time synchronized reverse vertical seismic profiles, as well as high‐resolution and good‐quality data in terms of S/N and high‐frequency content. The method improves the use of the working drill bit as a downhole seismic source with different types of bit and drilling conditions.

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