Drill-bit seismic monitoring while drilling by downhole wired-pipe telemetry

摘要

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.