Abstract. Acoustic energy emitted by drill bits can be recorded by
geophones on the surface and processed for an image of the subsurface using
seismic interferometry methods. Pilot sensors record bit signals on the drill
rig and play an important role in processing geophone traces for the image.
When pilot traces are not available, traces of the nearest geophone to the
rig may be used in deconvolution and cross-correlation of data, but extra
signal processing efforts are required to reduce the effect of source
signature on cross-correlation results. In this study, we use the seismic
interferometry method to image the shallow subsurface beneath a 2-D geophone
array by converting geophones to virtual sources. As there is no pilot
signal available for this survey, we use the nearest geophone trace for pilot
cross-correlation and pilot deconvolution. We modify the spectrum of pilot
cross-correlation and deconvolution results so that the effect of source
function on virtual data is minimized. We then migrate the virtual shots and
compare the results of interferometric imaging with the available image from
3-D (active source) survey and assess the efficiency of our approach. We show
that drill bit noise data can be used to generate a reasonably accurate
image of the subsurface even in the absence of pilot recordings, but the
results should be checked for the appearance of virtual multiples and depth
inconsistencies that are caused by errors in the migration velocity.
Drill bit noise imaging without pilot trace, a near surface interferometry example
