Drill‐bit signal separation for RVSP using statistical independence

Abstract

Drill‐bit noise and RVSPs. Time and depth migration of seismic data usually is based on velocities estimated from surface measurements. The actual velocities, which calibrate the depth‐migrated seismic to the well data, are determined after the well is drilled using check shots and VSPs. By then, it may be too late to correct for seismic migration velocity imprecision and impact the well’s success. The earlier we can obtain such velocity information, the more time will be available for reprocessing (remigration of either the seismic or any depth maps), if necessary. It is therefore very useful to determine the velocities to calibrate seismic and well velocities while drilling. This allows us to better locate the drill bit in time on the seismic section; to redirect the well, if necessary; and to gather as much further information as possible on the rocks ahead of the bit.

Subsurface seismic imaging with a hammer drilling source at an exploration drilling test center in Örebro, Sweden

“…The idea of using the drill-bit as a seismic source has been around since the late 1980s or earlier (Rector and Marion, 1991) and has been advocated by a number of researchers over the years (e.g. Malusa et al, 2002;Poletto and Dor-dolo, 2002;Poletto et al, 2012;Petronio and Poletto, 2002;Bakulin et al, 2020). The basic principle is that the seismic signal generated by the drill-bit is simultaneously recorded by a pilot sensor mounted on the top of the drill string and by seismometers deployed on the surface at multi-offset positions from the borehole or in a second borehole.…”

Retrieving virtual reflection responses at drill‐bit positions using seismic interferometry with drill‐bit noise

“…Besides passive noise, active noise with known locations, such as drill-bit noise, has long been used in seismicwhile-drilling (SWD) to obtain reverse vertical seismic profiles (Rector and Marion 1991; and to provide look-ahead information while drilling (Malusa, Poletto, and Miranda 2002;Eidsvik and Hokstad 2006). Most methods in SWD rely on pilot signals (estimates of the seismic signature of the drill bit) to compress the drill-bit signal to an impulse (Rector and Marion 1991;Poletto, Rocca, and Bertelli 2000;Poletto et al 2014). Standard SWD processing involves cross-correlation of pilot signals and geophone recordings, reference deconvolution, and pilot-delay shift.…”

“…Most methods in SWD rely on pilot signals (estimates of the seismic signature of the drill bit) to compress the drill-bit signal to an impulse (Rector and Marion 1991;Poletto, Rocca, and Bertelli 2000;Poletto et al 2014). Standard SWD processing involves cross-correlation of pilot signals and geophone recordings, reference deconvolution, and pilot-delay shift.…”