Abstract: An acoustic array includes an acoustic transmitter and acoustic receivers radially or longitudinally offset from the acoustic transmitter. The acoustic array is disposed in a wellbore penetrating a subsurface formation. An acoustic signal is broadcast using the transmitter and a portion of the emitted signal is reflected by a reflector and received by the receivers. The presence or absence of fractures in the subsurface formation is inferred based on the received acoustic signal. Inferences are based on travel times and/or coherency of the received signals. Images can be made and fracture orientations determined. Frequencies in the sonic or ultrasonic range may be used. Measurements may be made while-drilling or while performing post-drilling operations. Processing may be done in real-time or post-processing may be performed on recorded data.

Abstract: Methods and systems for identifying and locating fractures within a wellbore are described herein. One such method includes generating an acoustic wave. At least a first portion of the acoustic wave travels along a wall of the wellbore. The first portion of the acoustic wave interacts with a feature on the wall of the wellbore, such as a fracture, and generates a second acoustic wave. The second acoustic wave is detected to obtain acoustic data. A chevron pattern is identified within the acoustic data and a location for the feature is determined using the identified chevron pattern.

Abstract: An acoustic array includes an acoustic transmitter and acoustic receivers radially or longitudinally offset from the acoustic transmitter. The acoustic array is disposed in a wellbore penetrating a subsurface formation. An acoustic signal is broadcast using the transmitter and a portion of the emitted signal is reflected by a reflector and received by the receivers. The presence or absence of fractures in the subsurface formation is inferred based on the received acoustic signal. Inferences are based on travel times and/or coherency of the received signals. Images can be made and fracture orientations determined. Frequencies in the sonic or ultrasonic range may be used. Measurements may be made while-drilling or while performing post-drilling operations. Processing may be done in real-time or post-processing may be performed on recorded data.

Abstract: Methods and systems for identifying and locating fractures within a wellbore are described herein. One such method includes generating an acoustic wave. At least a first portion of the acoustic wave travels along a wall of the wellbore. The first portion of the acoustic wave interacts with a feature on the wall of the wellbore, such as a fracture, and generates a second acoustic wave. The second acoustic wave is detected to obtain acoustic data. A chevron pattern is identified within the acoustic data and a location for the feature is determined using the identified chevron pattern.

Abstract: Tube waves are used to locate and characterize a solids deposit inside a fluid-filled pipe. An acoustic tube wave pulse is transmitted along the pipe. On encountering a solids deposit, the tube wave pulse is perturbed and partially reflected by changes in the boundary conditions between the fluid and the pipe to produce two deposit-modified acoustic waves. One is a perturbed wave travelling in the same direction as the tube wave pulse. The other is a reflected wave travelling in the opposite direction. One of these deposit-modified acoustic waves is received to produce an acoustic signal. Accumulated acoustic signals are processed by Fast-Fourier Transform to produce frequency-based digital data. Phase data from the frequency-based digital data is inverted to produce slowness spectrum data. Power data from the frequency-based digital data is inverted to produce attenuation spectrum data. Spectrum data is used to locate a solids deposit in the pipe.

Abstract: Methods and tools are provided for real time velocity imaging of a borehole wall with sufficiently high resolution to identify vugs, worm holes, thin beds, dip angles, fractures and breakouts, for both open hole logging and logging while drilling in the presence of OBM's. A method is provided which includes transmitting an ultrasonic pulse through the borehole wall, receiving at first and second spaced-apart receivers an ultrasonic pulse refracted from the borehole wall, and producing a velocity image data value indicative of difference of arrival times at first and second spaced-apart receivers. This is repeated at a plurality of azimuths and depths to produce a velocity image data set. The method uses compressional pulses and/or pseudo-Raleigh pulses. A tool is provided for wireline use having an ultrasonic transmitter for transmitting ultrasonic pulses into the borehole wall, and a plurality of ultrasonic receivers.

Abstract: Tube waves are used to locate and characterize a solids deposit inside a fluid-filled pipe. An acoustic tube wave pulse is transmitted along the pipe. On encountering a solids deposit, the tube wave pulse is perturbed and partially reflected by changes in the boundary conditions between the fluid and the pipe to produce two deposit-modified acoustic waves. One is a perturbed wave travelling in the same direction as the tube wave pulse. The other is a reflected wave travelling in the opposite direction. One of these deposit-modified acoustic waves is received to produce an acoustic signal. Accumulated acoustic signals are processed by Fast-Fourier Transform to produce frequency-based digital data. Phase data from the frequency-based digital data is inverted to produce slowness spectrum data. Power data from the frequency-based digital data is inverted to produce attenuation spectrum data. Spectrum data is used to locate a solids deposit in the pipe.

Abstract: A method provides for locating and measuring mechanical damage in rock surrounding a borehole by detecting one or both of reductions in ultrasonic compressional wave velocity in the rock as a function of azimuth, and by detecting focused acoustic energy in the rock from local increases in ultrasonic compressional wave amplitude resulting from velocity gradients. A first preferred embodiment uses a combination of azimuthal ultrasonic compressional wave velocity data and azimuthal ultrasonic compressional wave energy data. A second embodiment uses azimuthal ultrasonic compressional wave velocity data and omni-directional sonic velocity data, with a comparison test or a curve fitting test. A third embodiment uses azimuthal ultrasonic compressional wave energy data.

Abstract: A method for determining whether a formation is subject to incipient failure are disclosed. The method comprises determining in situ a nonlinear parameter of a formation, and determining whether the nonlinear parameter and/or a derivative of that nonlinear parameter as a function of stress has a relatively large negative value in order to determine whether the formation is subject to incipient failure. In a preferred embodiment, the nonlinear parameter of the formation is a derivative of the square of the shear or compressional velocity with respect to formation stress. The nonlinear parameter of the derivative of the square of the shear velocity with respect to stress is considered to have a large negative value when it is .ltoreq.-0.1 (km/sec).sup.2/ MPa, while the nonlinear parameter of the derivative of the square of the compressional velocity with respect to stress is considered to have a large negative value when it is .ltoreq.-0.2 (km/sec).sup.2 /MPa.

Abstract: Borehole tools are provided with at least one transmitter which generates acoustic waves at a plurality of azimuthal locations about the borehole, and at least one receiver which receives and measures a characteristic (e.g., velocity) of the acoustic waves at related azimuthal locations. The direction of minimum velocity around the borehole is considered the direction of maximum uniaxial stress in the formation. From the velocity as a function of azimuth information, determinations of formation properties, and logs of the same can be made. The azimuthal direction of minimum velocity around the borehole predicts the propagation direction of artifically induced hydrofractures. The velocity variation around the borehole at a particular depth of the borehole is taken as an indication of susceptibility to failure, with higher velocity variations indicative of a more poorly consolidated formation or a formation with a large uniaxial stress.

Abstract: Apparatus and methods for determining an indication of a nonlinear property of a formation traversed by a borehole are provided. An acoustic tool is used in a borehole to generate first and second signals of different frequencies. As a result of nonlinearities in the formation, the mixing of the first and second signals results in a third signal having a frequency equal to the difference of the frequencies of the first and second signals. The amplitude of the third signal is measured by a detector, and the indication of nonlinearity of the formation is determined according to a relationship which relates the measured amplitude at the measured frequency to the amplitudes of the first and second signals, the frequency of measurement, the velocity of the measured wave, the distance of the receiver from the source, and a function of the nonlinear and linear parameters of the formation.