Subsurface seismic imaging using drill bit noise

SummaryAcoustic signal generated by drill bit cutting action in the borehole can be recorded passively by geophones on the surface and used to produce an image of the subsurface under the geophone array. A single pilot trace is commonly recorded on the drill string and used to convert geophone recordings to equivalent reverse vertical seismic profile data. If there is no pilot measurements on the drill string, seismic interferometry can be used to move continuous sources of energy from the bottom of the borehole to the surface and use conventional seismic methods to image the subsurface.In this study, we recorded the noise coming from drilling operation for several shallow wells over the surface of a small iron ore prospect in Pilbara region of Western Australia. As pilot measurements were not available, we used seismic interferometry to produce virtual shots on the surface. We then migrated virtual data generated along one receiver line for one deep well and four shallower wells over the line. We saw that only deep well with longer drilling time can produce a seismic image with coherent events that are comparable to 3D surface seismic data.