Patent ID: 6262941
Filing Date: 2001-07-17
Classification: G01V

Abstract:
A method for seismic prospecting while drilling a well through a formation to be investigated by using elastic waves generated by a bottom hole assembly including a drill bit associated with drill collars advancing at a bottom of the well and connected to surface drilling equipment by a drill string, the method comprising:receiving vibrations coming from the formation in response to the elastic waves provided by the bottom hole assembly by a set of seismic receivers coupled with the formation;recording signals generated by the seismic receivers when receiving the elastic waves and correlating the recorded signals with reference signals representing the imparted elastic waves;using as the reference signals signals sensed by a reference sensor positioned on and coupled with the drill string below a surface of the formation; andattenuating vibrations propagating towards the drill string with a dampening assembly including a first dampening device positioned in the bottom hole assembly below the reference sensor to maintain the drilling tool substantially in contact with the bottom of the well, with a second dampening device interposed into the drill string to reduce the parasitic emissions in the formation, and with a filter including at least one pipe portion with a diameter intermediate between a diameter of the drill collars and a diameter of the drill string, the length of the pipe portion being chosen as a function of wavelengths in a seismic frequency range, to attenuate in the seismic frequency range multiple reflections due to discontinuities in diameter of the pipe portion intermediate between the drill collars and the drill string and the reference sensor is disposed beneath the second dampening device.