Abstract: A multi-part logging tool that allows measurement of several distinct independent parameters, which are in turn used to solve for secondary parameters that give information about the properties of the cement outside the casing. Secondary parameters affecting the measured signals are: casing thickness, bond of cement to casing, cement acoustic impedance, cement thickness, channel size and channel material. The present invention comprises a rotating tool that supports a plurality of specifically configured transducers that interrogate a region behind casing having a 10 degree azimuthal resolution and a depth of investigation of at least 0.75 inches behind casing. The transducers on the rotating tool include an array of angled beam transducers, a single-housing pitch-catch transducer and a radial, pulse echo transducer.

Abstract: A standoff compensation system is disclosed for use in an acoustic LWD system. An acoustic transducer is provided to measure the standoff distance between the logging tool and the borehole wall. The present invention includes a downhole processor for determining an index value which is used to align received acoustic formation signal measurements based upon the measured standoff distance. The index value can either be calculated by the downhole processor or can be retrieved from a pre-calculated look-up table in ROM. The processor then shifts the received acoustic formation signals based upon the index value assigned to each formation signal. The aligned acoustic formation signals are stacked, so that a single acoustic formation signal can be obtained for each firing period and either stored in downhole memory, used immediately, or transmitted by telemetry to the surface. The firing of the acoustic formation transmitters occurs in a rapid firing mode, followed by a relatively long idle.

Abstract: A LWD tool is disclosed for detecting the existence of and distance to adjacent bed boundaries. A transmitter assembly generates either a short acoustic pulse or a swept frequency signal that is detected by an associated receiver assembly. The received signal(s) are conditioned and converted to high precision digital signals by an A/D converter. The digitized signals are accumulated and transferred to a digital signal processor via a high speed data bus. The digital signal processor also receives a digital signal representing the transmission signal and compares the transmission signal and the received signals together to enable a downhole microprocessor to derive a time lag for the received signals.