Abstract: A reverse VSP system is provided and uses a frequency-controllable modulator of an MWD tool as a downhole seismic source. The modulator has a rotor and stator arranged to provide substantially sinusoidal outputs, and is controlled to provide a "Vibroseis"-type frequency sweep (preferably from 1 Hz to 50 Hz). With the bit of the MWD tool in contact with the bottom of the borehole, the force generated by the frequency-controllable modulator will generate measurable axial compressional (P-) waves. These waves which move through the formation are detected by an array of geophones on the formation surface, and a reference signal is obtained by a kelly-mounted accelerometer or strain gauge. The reference signal and signals obtained by the geophones are processed using known signal processing techniques.

Abstract: A reverse VSP system is provided and uses a frequency-controllable modulator of an MWD tool as a downhole seismic source. The modulator has a rotor and stator arranged to provide substantially sinusoidal outputs, and is controlled to provide a "Vibroseis"-type frequency sweep (preferably from 1 Hz to 50 Hz). With the bit of the MWD tool in contact with the bottom of the borehole, the force generated by the frequency-controllable modulator will generate measurable axial compressional (P-) waves. These waves which move through the formation are detected by an array of geophones on the formation surface, and a reference signal is obtained by a kelly-mounted accelerometer or strain gauge. The reference signal and signals obtained by the geophones are processed using known signal processing techniques.

Abstract: A new "radial" cement bond instrument is disclosed for measuring the quality of cement to casing bond. The instrument is capable of measuring the quality of the cement bond both vertically and circumferentially. Four arrays of sectored transmitters and receivers are arranged longitudinally along the instrument body and provide a compensated radial bond measurement with high azimuthal resolution. The sectored transmitter excites both a compressional wave and a shear wave in the casing, with the beam pattern of the transmitter focused in a radial direction. The sectored receiver provides additional directivity for enhanced detection of channels in cement. The disclosed apparatus provides measurement of the quality of cement bond in eight radial segments. The resolution of the instrument provides 5 to 10 percent overlap to insure "full" coverage of the borehole.