| 摘要 |
<p>A method for detecting the presences of fractures in a subsurface formation (20) being penetrated by a drill bit (24) during drilling. Teeth (38) on the drill bit act as individual seismic sources, generating both shear wave energy and compressional wave energy. As the drill bit passes through a formation, the shear wave energy generated by the bit propagates along the formation in a waveguide mode between the adjacent formations. As the shear wave signal passes through a fractured zone (65) of the formation (20), two shear wave signals (66 and 68) are generated, each polarized in relationship to the orientation of the fractures in the formation. As the polarized signals propagate along the formation, secondary shear wave signals (82) are generated which return to the surface and are detected by appropriate sensors. The sensors have a plurality of detectors in order to detect the polarity or direction of particle motion caused by the polarized wave, providing information that a fracture zone exists in the subsurface.</p> |
