METHOD OF SONIC LOGGING WHILE DRILLING A BOREHOLE TRAVERSINGAN EARTH FORMATION

摘要

The present invention is directed to sonic logging while drilling. A transmitter and at least one receiver are mounted on a drill collar for peforming sonic investigations of the formation traversed by a borehole. It has been discovered that a drill collar has a natural stop band or notch where acoustic energy propagating in this frequency range is severely attenuated. Thus, to reduce drill collar acoustic coupling, the transmitter is operated within this natural stop band of the drill collar. An imperforate stop band filter is also included between the transmitter and receiver to enhance the natural stop band. The ~ ",ill~l is mounted transverse to the longitudinal axis of the drill collar, and is preferably mounted within means that reduce drill collar acoustic coupling. The transmitter preferably inrhl(les a material whose acoustic response is more favorable along its longitudina1 axis relative to its radial axis, thereby directing the acoustic energy into the formation rather than the surrounding drill collar. Received acoustic energy waveforms are electronically processed to reliably detect, in the presence of drilling noise, those acoustic signals which are produced by the transmitter and transmitted through the formation.