Abstract: A logging instrument is caused to traverse a cased earth borehole periodically emitting and receiving acoustic energies, such instrument generating an electrical signal containing one or more electrical alternations representative of the received acoustic energies, and such alternations having an amplitude generally functionally related to the attentuation of the acoustic energies as they traverse the casing within the borehole. A significant portion of these alternations is determined and digitized, and the individual digitized values therein summed together to yield a functional representation of the signal area of the alternations of a predetermined polarity within the significant portion. This signal area is then compared to the area which would be indicated if the casing were free of cement bonding, the comparison yielding an indication of the relative degree of bonding of cement to the casing within the borehole.

Abstract: In an acoustic logging system for providing information regarding selected parameters of the wall of a borehole in the earth, and of the rock formation which is adjacent the borehole, in which a single transmit/receive transducer system (T/RTS) mounted on a rotating assembly probes the wall of the borehole in a circular scanning pattern as a function of depth, the improvement which includes at least a second T/RTS mounted on the rotating assembly in known geometrical relation to the first T/RTS, and means to process two or more analog electrical scan signals for transmission over one or more electrical transmission channels in a logging cable. In particular, methods and means are described for transmitting multiple scan signals whereby a higher speed of logging is possible without loss of detail of the logs and without modification of the mechanical system of the logging sonde.

Abstract: Method and apparatus are provided for measuring acoustic signals having amplitudes of widely varying magnitude during one traversal of the borehole corresponding to indications of cement bonding along a casing as well as acoustic travel time through an increment of the formation. Variable attenuators are provided associated with acoustic receivers disposed within the logging sonde wherein attenuation may be automatically adjusted as a function of acoustic transmitter-receiver trigger pulses transmitted downhole, depending upon whether a cement bond or other log of acoustic signal information having a substantially different magnitude is desired.

Abstract: A method for determining the lithology of subterranean structures based on attenuation of wave energy is disclosed which features a wave model based on a two-way solution to the wave equation rather than one-way solutions previously proposed. Rather than measuring amplitude of the wave as a function of its attenuation, energy flux density is measured which provides a two-way wave solution. In a preferred embodiment, pressure gradient measuring transducers are used to measure the energy flux density.

Abstract: Apparatus and method for sonic borehole logging using a continuous wave transmitted signal. The transmitted signal is received at a plurality of points distributed along the borehole axis and sampled synchronously with the transmitted signal. The resulting sampled signal is analyzed, for example, by Fourier analysis, to identify each spatial frequency component. Each frequency component identified indicates the velocity of a particular acoustic wave path from the transmitter to the receiver.

Abstract: An improved well logging technique is provided for more accurately deriving measurements of sub-surface earth formations, for processing and recording such measurements to record them in reproducible form, and to more informatively display such measurements. Other significant features and aspects of the overall technique include improved methods and apparatus for deriving such measurements in digital form and for merging or combining two or more such measurements in one storage.In a particular embodiment of the invention, the logging sonde is provided with means for forming the logging data into discrete "frames" of data expressed in digital form, and for delivering such frames of data to the surface preferably in response to a command signal which is generated at the surface in correlation with the depth of the sonde in the borehole.

Abstract: A well-logging method and apparatus in which a fast real time portion of a logging signal is sequentially sampled at discrete times. These sampled segments are stored and then are clocked out of storage over an expanded time period.The rms amplitude portion of the logging signal occurring prior to the compression wave part of the logging signal (the nominal noise level) may be used for AGC regulation of an amplifier which amplifies the time-expanded output.A similar development of an rms value can be used for establishing a threshold level for a peak detector, which level is set slightly higher than such rms value. The first three successive samples greater than the threshold level detected by the detector are presumed to be the first three samples of the compression wave. This presumed compression wave is recorded and convolved against the expanded-time digital form of the logging signal to locate the compression wave in a second received signal and, later, the similarly appearing "shear" wave.

Abstract: A technique for producing measurements of physical characteristics of subsurface media near a borehole penetrating the earth is disclosed that uses multiple transducers positioned along a borehole tool. A number of transducers of a first type, such as transmitters, are separated from each other along the tool by a preselected separation, and a number of transducers of a second type, such as receivers, are separated from each other by the same separation and are positioned on the tool at a preselected distance from the transducers of the first type. The technique contemplates the use of appropriate circuitry for producing measurements, using different combinations of transducers, of physical characteristics of the subsurface media at different positions along the borehole.Furthermore, different combinations of measurements produced at different borehole positions may be compared or combined to produce improved measurements that are compensated for borehole effects and other errors.

Abstract: Acoustic well-logging methods and apparatus are provided for investigating earth formations traversed by a borehole. Acoustic waves are transmitted from different points in the borehole and received at other points in the borehole, and a reception signal is generated representative of the received acoustic waves. The time interval between the instant the measurement waves are transmitted and the instant the instantaneous amplitude of the reception signal exceeds a given detection threshold for the first time is measured as a function of depth and the value of the detection threshold is adjusted during each measurement sequence in accordance with the amplitude of the noise received during the next preceding listening interval.

Abstract: Bursts of signals at different frequencies are induced into substructure, adjacent a borehole. The return signals from each burst of signals are normalized to compensate for the attenuation, experienced by more distant return signals. The peak amplitudes of return signals, above a selected level, are cut off, and an average signal is produced from the normalized amplitude-limited return signals of each burst. The averaged signals of the return signals of all the signal bursts at the different frequencies are processed, to provide a combined signal, whose amplitude is related to the microfracture density of the substructure adjacent the borehole.