Abstract: A method and apparatus useful to determine the integrity of a cement bond log disposed in the annular space between a casing and a wellbore. The method and apparatus induce a Lamb wave in the casing and into the wellbore. The Lamb wave attenuates upon passage through the cement bond log. The integrity of the cement bond log can be determined through an analysis and evaluation of the attenuation results.

Abstract: A method waveform processing technique utilizing signal coherence of the array data for processing signals having poor signal-to-noise ratio. Raw waveform data is first transformed into f-k (frequency-wavenumber) domain. A coherence function is then calculated and convolved with the data in the f-k domain, which effectively suppresses non-coherent signals in the data. For the remaining coherent data, the unwanted part is muted and the wanted part is retained and inverse-transformed to yield the coherence-filtered array waveform data. After this processing, small signals that are hidden in the original data are extracted with much enhanced coherence. Subsequent processing of the data yields reliable information about formation acoustic property.

Abstract: Passive and active suppression of casing signals is used to improve the ability to measure formation velocities. Passive suppression includes the use of a magnet slidably coupled to the casing. Active suppression uses measurement of casing signals to control the output of an electromechanical acoustic transducer which cancels the propagating signal. Feedback control may be provided.

Abstract: Disclosed herein is a method of delineating a second wellbore from a first wellbore. The method includes, emitting acoustic waves from a tool in the first wellbore, receiving acoustic waves at the tool reflected from the second wellbore, and determining orientation and distance of at least a portion of the second wellbore relative to the tool.

Abstract: A phased array of transducers is used to generate elastic waves into the earth formation in a selected direction. The impedance measured at the input to the transducer array is indicative of the elastic impedance of the earth formation in the selected direction.

Abstract: Acoustic measurements made in a borehole using a multipole source are used for imaging a near-borehole geological formation structure and determination of its orientation. The signal to noise ratio (as defined by the ratio of the signal radiated into the formation to the axially propagating signal) depends upon the type of source (force or volume) and its position in the borehole (on the tool, in the fluid or on the borehole wall).

Abstract: Cross-dipole measurements are obtained in a borehole. By estimating a direction of polarization of the fast shear mode at low and high frequencies and comparing the estimated distances, a cause of anisotropy is established. Formation stresses and directions may be estimated.

Abstract: A method and apparatus useful to determine the integrity of a cement bond log disposed in the annular space between a casing and a wellbore. The method and apparatus produce a transversely polarized shear wave and emit the wave through the casing and into the wellbore. The transversely polarized shear wave attenuates upon passage through the cement bond log. The integrity of the cement bond log can be determined through an analysis and evaluation of the attenuation results.

Abstract: A method and apparatus for enhancing the moveout between a direct wave and a reflected wave. The method involves transmitting imaging signals into a body to be imaged and receiving the resulting signals propagated from the signal source. The step of receiving the propagated signals includes selectively adjusting the distance between the signal source and the signal receivers between successive signals. The method further comprises separating the reflected signals from the total received signals and enhanced stacking of the measured reflected signals.

Abstract: A downhole acoustic logging tool uses a phased-array of transmitters and/or receivers to improve the signal level of compressional waves generated by the transmitters and propagating in the formation. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Abstract: Stoneley-wave data acquired in the LWD environment are used to characterize/estimate formation permeability. Real-time Stoneley-wave time-delay/slowness and center-frequency/attenuation data are used to indicate/characterize formation permeability even during drilling. The use of stabilizers mounted at the tool ends helps maintain the tool position from severe decentralization, reducing ambiguities in the permeability characterization/estimation. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Abstract: The method disclosed is useful for estimating anisotropic properties of an earth formation. The method includes extracting travel time values of components of the acoustic wave induced from a downhole tool and reflected from a boundary bed formation. The method further includes obtaining a travel time ratio of the wave components and using the travel time ratio to estimate the anisotropic properties of the formation.

Abstract: Shear wave reflection data obtained by a cross dipole tool are rotated to a fixed coordinate system and migrated to produce an image of an earth formation.

Abstract: A method and apparatus for assessing the permeability of a subterranean formation and the hydrocarbon and/or water content of the formation. The method includes emitting an acoustic signal, such as a Stoneley wave into the formation and sending an electro-magnetic pulse into the formation. An analysis of the response of the Stoneley wave in conjunction with an analysis of a measurement of the electrical potential within the wellbore provides information pertinent to permeability and fluid composition.

Abstract: A method and apparatus for evaluating a bond between a formation and a bonding material. The method includes emitting a shear wave into the tubular, recording the response of the shear wave, and evaluating the response to obtain bond information. The bond information includes bond material thickness and efficacy of the bond between cement and formation. The method includes studying and utilizing the time lag of the direct wave and wave events, as well as the interference of these waves on a spectral graph. A calibration method is included as well.

Abstract: A phased array of transducers is used to generate elastic waves into the earth formation in a selected direction. The impedance measured at the input to the transducer array is indicative of the elastic impedance of the earth formation in the selected direction.

Abstract: A method and apparatus useful to determine the integrity of a cement bond log disposed in the annular space between a casing and a wellbore. The method and apparatus induce a Lamb wave in the casing and into the wellbore. The Lamb wave attenuates upon passage through the cement bond log. The integrity of the cement bond log can be determined through an analysis and evaluation of the attenuation results.

Abstract: Directional acoustic measurements made in the borehole are used for imaging a near-borehole geological formation structure and determination of its orientation. Four-component cross-dipole data set measured in a deviated borehole in combination with the directionality of the compressional waves in the dipole data give the orientation of bed boundaries crossing the borehole. The low-frequency content (2˜3 kHz) of the data allows for imaging the radial extent of the formation structure up to 15 m, greatly enhancing the penetration depth as compared to that obtained using conventional monopole compressional-wave data. A combination monopole/dipole arrangement of sources and receivers may also be used for imaging of bed boundaries.

Abstract: The logging tool of this invention includes a transmitter conveyed on a drilling collar for exciting a quadrupole signal in a borehole being drilled by a drill bit and a receiver for receiving the signal. The transmitter is operated at a frequency below the cut-off frequency of the quadrupole collar mode. The received signal consists primarily of the formation quadrupole mode which, at low frequencies, has a velocity that approaches the formation shear velocity. The transmitter, in one embodiment, consists of eight equal sectors of a piezoelectric cylinder mounted on the rim of the drilling collar. The value of the cut-off frequency is primarily dependent on the thickness of the drilling collar. Alternatively, the transmitter may be operated to produce both the collar mode and the formation mode and a processor may be used to filter out the collar mode.

Abstract: A method and apparatus useful to determine the integrity of a cement bond log disposed in the annular space between a casing and a wellbore. The method and apparatus produce a transversely polarized shear wave and emit the wave through the casing and into the wellbore. The transversely polarized shear wave attenuates upon passage through the cement bond log. The integrity of the cement bond log can be determined through an analysis and evaluation of the attenuation results.