| 摘要 |
An acoustic formation apparatus is set forth. It utilizes the drill bit on a drill stem as the acoustic source. At a common azimuth and spaced vertically along the drill stem, first and second acoustic transducers are installed. They connect to first and second amplifiers, first and second band pass filters, first and second clipping circuits, a single delay circuit and a cross correlating circuit. The signals are received, filtered, amplified, clipped, one delayed, and then cross correlation is made utilizing variable time delays. The resulting cross correlation function is analyzed using a microprocessor which removes stationary correlation peaks and ignores very short correlation delay times. This enables removal of the substantially fixed aspect of the pipe transmitted signal and the very fast propagating waves so that the processed cross correlation function output is substantially related to the formations and the larger, over powering signal transmitted along the drill string through the steel pipe making up the drill collars is substantially avoided.
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