Abstract: Acoustic signals sent by a logging tool disposed in a borehole are detected by receivers located on the logging tool. Time domain representations of the detected acoustic signals are converted into frequency domain representations. Then at least one frequency range is selected and the detected acoustic signals corresponding to each selected frequency range are filtered. Eigenvectors for the filtered data for each selected frequency range are computed and dependence of the eigenvectors on the frequency is obtained. System for processing acoustic signals comprises a computer in communication with the logging tool and a set of instructions executable by the computer.

Abstract: The acoustic logging tool comprises at least one emitter and at least two receivers. The receivers are installed in positions having different azimuthal coordinates and are capable of measuring a wave field at points located at different distances from a vertical axis of the tool. The receivers are installed so that it is possible to change azimuthal or radial position of the receivers during measurements or both.

Abstract: The invention relates to the area of borehole acoustics, in particular, to monitoring a logging tool position in a borehole, namely detection and estimation of a borehole logging tool eccentricity based on the measurement and analysis of mixed surface waves waveforms. The method is characterized by the steps of registering acoustic signals generated by passage of acoustic waves in the borehole while logging and detecting the misalignment of the logging tool to the axis of the borehole by the presence of mixed surface waves. A system for monitoring a looging tool position in a borehole comprising means for registering acoustic signals generated by passage of acoustic waves while logging and data processing means for detecting mixed surface waves propagating along the borehole wall.

Abstract: A method for processing acoustic waveforms comprises acquiring acoustic waveforms in a borehole traversing a subterranean formation and transforming at least a portion of the acoustic waveforms to produce frequency domain signals. Then model dispersion curves are generated based on an anisotropic borehole-formation model having a set of anisotropic borehole-formation parameters. The frequency-domain signals are back-propagating using the model dispersion curves to correct dispersiveness of the signals and coherence of the back-propagated signals is calculated. Alternatively the difference between the measured and the model dispersion curves is determined. Model parameters are iteratively adjusted until the coherence reaches a maximum or exceeds a selected value, or alternatively until the difference between the measured and the model dispersion curves becomes minimal or is reduced to below a selected value. Then at least a portion of the set of anisotropic borehole-formation parameters is obtained.

Abstract: A pressure response to low frequency harmonic pressure oscillations generated in a borehole by at least one oscillation source is registered by at least one acoustic sensor. A phase shift of stationary pressure oscillations registered by the acoustic sensor relatively to the low frequency harmonic pressure oscillations of the oscillation source and a ratio between an amplitude of the stationary pressure oscillations registered by the acoustic sensor and an amplitude of the low frequency harmonic pressure oscillations of the oscillation source are determined. A thickness of a mudcake is determined and based on the results a cake piezoconductivity or a fluid mobility or both are determined.

Abstract: At least one acoustic sensor registers a pressure response to a low-frequency non-oscillating pressure signal generated in a borehole by at least one source. At least one characteristic of a transient process of pressure change is determined from the registered signal. A thickness of a mudcake is determined. Then, based on the values received, a mudcake piezoconductivity or a fluid mobility or both are determined.