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.