Abstract: Techniques for calculating and visually presenting multiple acoustic modes that have different formation slowness are disclosed herein. The techniques include methods for receiving time-domain waveforms from adjacent formations in a borehole, processing each of the time-domain waveforms to generate frequency-domain spectrums, selecting frequency and slowness values, and predicting travel time of a mode associated with the slowness value. In some aspects, the method further includes steps for calculating a semblance difference of the frequency-domain spectrums based on the frequency value, the slowness value and the predicted travel time. Systems and computer-readable media are also provided.

Abstract: The subject technology relates to estimation of flow rates using acoustics in a subterranean borehole and/or formation. Other methods, systems, and computer-readable media are also disclosed. The subject technology includes drilling a wellbore penetrating a subterranean formation. The subject technology includes logging the wellbore using an acoustic sensing tool to obtain logged measurements, and obtaining acoustic pressure data associated with a leak source in the wellbore using the logged measurements. The subject technology also includes determining a flow rate (volumetric for fluid-based or mass for gas-based) of the leak source from the acoustic pressure data, and determining an area of the leak source from the determined flow rate. The subject technology also includes generating and providing, for display, a representation of the leak source using the flow rate and the area of the leak source.

Abstract: Methods, systems, devices, and products for formation evaluation. Methods include automatically characterizing an acoustic reflective boundary in the earth formation by: generating a plurality of multipole acoustic signals within the borehole; generating acoustic wave data at at least one acoustic receiver on the logging tool in response to a plurality of acoustic reflections of acoustic waves from a corresponding plurality of reflection points along the boundary responsive to the multipole acoustic signals; estimating from the acoustic wave data a location in the formation for each reflection point of the plurality of reflection points, which may include performing coherence processing on at least a portion of the acoustic wave data to generate a coherence map; and identifying acoustic reflections from the coherence map; and using the location in the formation for each reflection point to estimate at least one property of the acoustic reflective boundary.

Abstract: Methods and apparatus for waveform processing are disclosed. An example method includes determining shrinkage estimators in a Discrete Radon transform domain based on semblance of waveform data and de-noising the waveform data using a processor and the shrinkage estimators to enable the identification of weak signals in the waveform data.

Abstract: Disclosed herein is an approach to improving the accuracy of signal-peak tracking in acoustic logs by supplementing a semblance method used to detect signal peaks in individual coherence-, correlation- or amplitude-based semblance maps with consistency checks based on rock-physics constraints and/or based on history and/or future data for the signal of interest.

Abstract: Systems and methods for simultaneously correcting the effects of deviation and dispersion on sonic log measurements of deviated wells in laminated formations and validating the corrected sonic log measurements using rock physics cross-plots.

Abstract: A technique facilitates enhanced microseismic monitoring. The technique may be applied to source mechanism identification under, for example, ill-conditioned receiver coverage to enhance the resolvability for microseismic monitoring. The microseismic monitoring may be used in hydraulic fracturing monitoring, induced seismicity monitoring, CO2 injection monitoring, other injection monitoring, mining, and/or other techniques which cause microseismic events.

Abstract: A method of estimating a parameter of an anomaly in an earth formation includes: disposing a measurement device at at least one measurement location, the measurement device including a frequency standard; estimating a frequency shift of a frequency standard due to a gravitational potential at at least one measurement location; and deriving a relationship between a mass and a depth of a formation anomaly at a distance to the at least one measurement location using the frequency shift.

Abstract: Methods and apparatus to filter acoustic waveforms in downhole environments are described. An example method involves receiving acoustic waveform data representing acoustic signals traversing at least a portion of a borehole adjacent a subterranean formation and performing a direct transform operation on the acoustic waveform data to generate wavelet map data. The wavelet map data comprises a time-frequency representation of the acoustic waveform data.

Abstract: A method for determining relative location of an acoustic event along a channel such as a wellbore includes obtaining two acoustic signals at are obtained at two different and known depths in the wellbore, dividing the acoustic signals into windows, and determining the relative loudnesses of pairs of the windows. The power of the acoustic signals may be used as a proxy for the loudness of the acoustic event, and this determination can be made in the time or frequency domains. The relative depth of the acoustic event can then be determined relative to the two known depths from the relative loudnesses. The acoustic event may be, for example, casing vent flow, gas migration, a leak along a pipeline, or sounds observed in an observation well from a nearby well in which fracking is being performed.

Abstract: A method for determining on a real time logging while drilling (LWD) basis gas within earth formations traversed by a borehole. Continuous LWD acoustic measurements are recorded and processed including coherent energy and attenuation attributes to detect downhole gas zones and kick during drilling operations.

Abstract: Multipole acoustic logging-while-drilling (LWD) tools and associated methods are disclosed herein. In some embodiments, the disclosed acoustic LWD tool comprises a transmitter array and at least one receiver array. The transmitter array generates acoustic waves with an excitation pattern having a cutoff frequency greater than about 3 kHz. The receiver array is spaced apart from the transmitter array and is configured to detect said acoustic waves. Some of the disclosed method embodiments comprise: generating multipole acoustic waves in a fluid-filled borehole using an excitation pattern with a cutoff frequency greater than about 3 kHz; selectively detecting acoustic waves that propagate with said excitation pattern; and determining an acoustic shear wave slowness for a formation penetrated by the borehole.

Abstract: In some embodiments, an apparatus and a system, as well as a method and an article, may include selecting a plurality of signal thresholds T(i)=i*(TMAX/N) for i=2 to N comprising a positive integer greater than one. TMAX may be equal to AMAX/R, where AMAX=a maximum peak amplitude of a signal, such as an acoustic borehole signal, and R=a root-mean-square amplitude of the signal. Applying the plurality of signal thresholds T(i) to the signal to determine a corresponding plurality of peak amplitudes A(i) and signal travel times for selected ones of the plurality of signal thresholds T(i) may also be included.

Abstract: Methods and related systems are described for modified semblance criterions based on the approach of thresholding the signal energy. A first criterion is derived by posing the problem as that of detecting a signal with energy (or amplitude) greater than the specified threshold and deriving the generalized likelihood ratio test statistic. A second criterion is derived using the same method by posing the problem as that of rejecting any signal with energy (or amplitude) below a specified threshold and detecting it if its energy is above another threshold greater than or equal to the first. These appropriately modify the original semblance criterion which is shown to be equivalent to the GLRT test statistic in the absence of any threshold on the signal amplitude. In addition simpler modifications are also described. Tests on synthetic data illustrate the effectiveness of all these modifications which perform comparably well at suppressing unwanted arrivals while accurately processing the desired signals.

Abstract: In some embodiments, an apparatus and a system, as well as a method and an article, may include selecting a plurality of signal thresholds including a product of an integer ranging from about 2 to N and a ratio of a quotient of a maximum peak amplitude of the acoustic borehole signal and a root-mean-square amplitude of the acoustic borehole signal, to N. Applying the plurality of signal thresholds to the acoustic borehole signal to determine a corresponding plurality of peak amplitudes and signal travel times for selected ones of the plurality of signal thresholds may also be included.

Abstract: A method for automatic classification, according to various selection criteria, of seismic or microseismic events picked up by seismic receivers coupled with an underground formation under development, according to whether the events are purely of microseismic nature or depend, on any account, on artifacts related to the outer environment or to formation development or monitoring activities, and for selection of the significant parts of traces for the purpose of analysis. The method has an application for monitoring of production or storage reservoirs under development.

Abstract: The invention is a method for removing trapped water bottom multiples, receiver side peg-leg multiples, and source side peg-leg multiples from dual sensor OBC data, where the data includes both pressure signals and velocity signals. The pressure and velocity signals are compared to determine any polarity reversals between them. Polarity reversals are used to identify and separate up-going and down-going wavefields in the pressure and velocity signals. A matching filter is applied to a portion of the velocity signal where polarity reversals exist. The down-going wavefield is then estimated by calculating the difference between the portion of the velocity signal where polarity reversals exist and the portion of the pressure signal where polarity reversals exist and applying a scaling factor to the result. An attenuated up-going pressure wavefield is then determined by combining the estimated down-going wavefield and the pressure signal.

Abstract: The invention is a method and apparatus for acoustic logging including one or more acoustic transmitters and one or more acoustic receivers. One or more of the elements of a set made up of the acoustic receivers and acoustic transmitters are spaced radially apart from one or more of the remaining elements of the set. The acoustic receivers and acoustic transmitters are configured along with electronics and software incorporated in the tool to allow the acoustic receivers and acoustic transmitters to act as multi-pole receivers and multi-pole transmitters, respectively. The tool is configured to compute one or more acoustic velocities and to provide storage for unprocessed and processed, compressed and error correction coded data. The tool is configured to provide the data for transmission to the surface.

Abstract: A method for evaluating the coherence of environmental measurements of a given geological medium or field using well logging data is disclosed. A series of N geological parameters are each measured at a series of reference points found in reference wells within this medium. Each reference point is at a different depth and has known lithological characteristics, and the N measurements form a reference observation (Xi) corresponding to that point. The same N parameters are measured at application points found in one or more application wells, at depths identical to those of the reference points, forming an application observation (x) for each application point. A neighboring domain (Di) and acceptance class are defined for each reference observation (Xi). Each application observation (x) is then compared with all of reference observations (Xi) using a nearest-neighbor algorithm to determine the degree of membership of the application observation in each reference observation's acceptance class.

Abstract: A sonic or acoustic tool having a transmitter and a receiver and further having a receiver testing and calibration device is disclosed. Methods for testing and tuning acoustic receivers dynamically are also disclosed. The calibration device includes an acoustic signal generator in acoustic communication with a receiver or a plurality of receivers, where the generator generates an acoustic calibration signal or test signal which propagates to each receiver. The receiver response is monitored to determine receiver integrity and tune. Based on the response, the processing unit or units can adjust the receiver response or instruct tuning circuitry associated with the receiver to adjust the receiver response.

Abstract: A method of determining the acoustic impedance of a fluid in a borehole, by gating a reflected acoustic signal into a plurality of time slots, and comparing received energies of the signal for the time slots to obtain a value indicative of the acoustic impedance of the fluid. The value may be normalized to yield the acoustic impedance of the fluid using the acoustic impedance of, e.g., water as a calibration point. The comparison is performed by comparing a ratio of an integration of a first ring down time slot and a second ring down time slot, to an integration of an internal reflection time slot. The acoustic pulse may be generated using a transducer immersed in an intermediate fluid contained within a chamber defined in part by a plate in contact with the borehole fluid and having a thickness such that a mechanical resonance frequency of the plate in a thickness mode is substantially equal to a resonance frequency of the transducer.

Abstract: An improved technique for determining the thickness of a member, especially pipe such as fluid-filled casing in an earth borehole, includes the following steps: directing a pulse of ultrasonic energy toward the inner surface of the pipe, and receiving and storing, as a function of time, signals representative of ultrasonic energy reflected from the inner surface of the pipe; determining, from the stored signals, the arrival time of the initial echo from the inner surface; determining, from the stored signals, the arrival time and the amplitude of a first candidate initial echo from the outer surface of the pipe; performing a reverse search on the stored signals to determine, from stored signals at times earlier than the arrival time of the first candidate, the arrival time and the amplitude of a second candidate initial echo from the outer surface; comparing amplitudes of the first and second candidates, and selecting, based on the comparison, one of the first and second candidates as the actual outer surface

Abstract: The present invention relates to an acoustic logging system having a sonde for arranging in a borehole of a well such as an oil well. The sonde has at least one transmitter for providing at least one transmitter acoustic signal, and has receivers for responding to the at least one transmitter acoustic signal, for providing receiver signals containing information about properties of earth formations in the borehole. The acoustic logging system features one or more transducers, a light source, an optical fiber and a detection and management unit. The one or more transducers responds to the receiver signals from the receiver of the sonde, for providing one or more mechanical transducer forces containing information about the receiver signals. At least one transducer may be a piezoelectric or magnetostrictive transducer. The light source provides an optical signal.

Abstract: A discrete, minimally-equipped standard seismic calibration system is permanently installed over a subsurface reservoir structure that contains fluids of economic interest. Changes in the fluid content as a function of long-term time lapse may introduce changes in the acoustical characteristics of the reservoir rock layers, producing a corresponding change in the seismic signature recorded by the calibration system. The difference between two signatures over a selected time epoch defines a time-lapse calibration signature. The time lapse calibration signature can be applied to reduce the results of different conventional seismic data-acquisition systems of different vintages and technologies to a common standard.

Abstract: Methods and apparatus for generating an error bar (variance) log for a formation parameter are disclosed. According to the method, acoustic waveforms are detected at a plurality (M) of detectors which are a function of a source signal which has interacted with the formation and noise, and the detected waveforms are sampled and processed in order to obtain a semblance or a normalized mean square error. Using the semblance or the NMSE which is related to the semblance, a signal to noise ratio 2E/N.sub.0 can be found by recognizing that the semblance function has a non-central beta distribution whose mean is a function of the signal to noise ratio 2E/N.sub.0, the time-bandwidth product N, and M. The signal to noise ratio is then used to find the Cramer-Rao lower bound which is taken as an estimate of the variance. An error bar log is formed by repeating these steps at a plurality of locations along the borehole.

Abstract: Each source of an array of seismic signal sources is associated with one or several sensors (Ci) which pick up the impulses the associated source emits at the time of triggering. The device essentially includes an apparatus (6) for the acquisition and the storage of all the signals emitted by the sensors (Ci) and a shooting control apparatus (7), having memories for reference data, for triggering the seismic sources according to these reference data. A computer (10) is programmed to determine the reference data used for the triggering, preferable according to the signals from the sensors (Ci) acquired during the previous emission cycles and validated in order to check whether their form and/or arrival times are within fixed limits. This arrangement makes it possible to take into account the real working conditions of the emission array. The invention can be utilized in marine seismic prospecting.

Abstract: A borehole televiewer is modified to provide an improved signal-to-noise ratio by utilizing a series of receivers arranged in a planar array configuration with respect to a centrally located transmitting transducer. The array covers at least a 90.degree. quadrant of the tool, extending approximately 45.degree. on either side of the transducer to allow the receivers to capture all primarily reflected signals, both the specular component as well as the vertical and horizontal components of the scattered reflections. The signal-to-noise ratio is further enhanced by the use of a noise-dependent timing means, as well as signal conditioning and detection circuits for each of the receivers in the array.

Abstract: A well logging system includes a digital threshold crossing data generation system (TCDG System) disposed in a well tool, adapted to be disposed in a borehole, and a digital first motion detection (DFMD) software disposed in a memory of a well truck computer. The TCDG system generates a series of threshold crossings for each analog signal received from a receiver of the well tool, the threshold crossings including a plurality of threshold crossing events for each analog signal and representing compressed versions of digitized analog waveforms. The well logging truck computer receives the threshold crossing data from the TCDG system and executes the DFMD software. When the software is executed, a first set of compressional wave first arrival times are determined from a startup routine in the software using the threshold crossing data.

Abstract: A well logging system includes a digital threshold crossing data generation system (TCDG System) disposed in a well tool, adapted to be disposed in a borehole, and a digital first motion detection (DFMD) software disposed in a memory of a well truck computer. The TCDG system generates a series of threshold crossings for each analog signal received from a receiver of the well tool, the threshold crossings including a plurality of threshold crossing events for each analog signal and representing compressed versions of digitized analog waveforms. The well logging truck computer receives the threshold crossing data from the TCDG system and executes the DFMD software. When the software is executed, a first set of compressional wave first arrival times are determined from a startup routine in the software using the threshold crossing data.

Abstract: A method and apparatus are described for generating a quick look display of an acoustic investigation of a borehole wherein a parameter of interest is derived from vertically spaced sonic receivers and displayed in a laterally continuous display log where the parameter values from respective receivers are recorded at preassigned positions. A fracture sensitive parameter is measured such as the energy in a low frequency Stoneley wave and when the parameter values are laterally recorded areas indicative of fractures become visually enhanced particularly with a laterally expanded display log. Techniques for the detection and evaluation of fractures are described.

Abstract: In an acoustic well logging apparatus including one or two transmitters and having a pair of spaced apart receivers, two interval transit times are measured independently through a common zone of interest. The two independent measured values are then compared and the difference is then used in contrast with a threshold determinant based on the period of the transmitted pulses. This comparison shows a difference. If the threshold value is not exceeded by the difference value a quality indication is then obtained suggesting that the acoustic measurements did not suffer from cycle skipping. If the threshold value is exceeded by the difference value, then a possible cycle skip exists. If testing shows that a cycle skip does exist, then the error that it introduces is removed from the final log, and a quality indication is obtained suggesting that the answer is good and that a cycle skip error has been removed.

Abstract: Disclosed is sonic well logging which gives good results both in open and in cased boreholes. New use is made of the energy content output from a multireceiver tool to find a coherence measure for the received sonic energy and to find the peaks of that coherence measure at each depth level so as to produce a number of new logs of parameters of those peaks. Examples are a slowness/time coherence log for those peaks, as well as new logs related to the arrival times of the coherent energy associated with the peaks and the energy attenuation for those arrival times.

Abstract: A method and apparatus for estimating shear wave velocities where such velocities are difficult or impossible to measure because the shear energy transmission is attenuated or its velocity is equal to or less than direct mud velocity or because the shear wave may not propagate at all under certain conditions. The method and apparatus relate to an indirect technique for determining shear modulus by measuring the phase velocity of the Stoneley wave excitation and using it to estimate the shear modulus and the shear velocity. Using at least two receivers, a window is placed over the Stoneley arrival of the wave detected at each receiver and the Fourier transform of each wave is taken. The difference in phase of the Stoneley wave arrivals is determined. The relative shear modulus involving the Lame constants is estimated by a procedure which includes matching two points on Stoneley wave dispersion curves.

Abstract: Shear and compressional velocities of acoustic waveforms in the earth formations surrounding a well bore are measured by analyzing the waveforms propagated through different lengths of substantially the same formation intervals. Phase analysis techniques applied to waveforms windowed for compressional waves are used to determine the propagation velocity of the compressional waves through the differential path lengths. The waveforms are then windowed for shear waves, the discrete fourier transforms of the windowed waveforms are taken, and the cross-spectral magnitude and phase for each frequency is computed as the product of the discrete fourier transform sample of one with the conjugate of the other. Several different moveouts are calculated, the resultant phases from each analyzed, and a band specified where the zero phase moveouts are roughly consistent.

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 well logging method and apparatus for detecting the first arrival of an acoustic wave in a logging signal under adverse signal conditions. The received acoustic signal is amplified at a fixed gain until clipped at the largest amplitude throughout the logging procedure. This amplified signal is converted RMS to DC level signal and stored in sample and hold means for a period shortly before first arrival of the acoustic wave. The continuing DC level signal and the stored DC level signal are compared to produce a comparator output DC signal when the continuing DC signal has a certain increased magnitude. This certain increased magnitude is used to generate a pulse of given magnitude and duration that is especially suitable in digital data systems.

Abstract: An improved well logging technique is provided for more accurately deriving acoustic measurements of sub-surface earth formations. Method and apparatus are described for converting an acoustic signature which can be generated on a depth dependent or time dependent basis, into digital format and subsequently employing special processing techniques to yield parameters such as velocity of the transmitted acoustic energy through earth formations and the amplitude of the received acoustic energy. Processing further allows for the generation of noise immunity signals functionally related to a measured signature parameter and for the generation of amplitude control signals. Additionally, a control signal is generated to optimize transmitter firing rate.

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: The disclosure relates to a method and apparatus for acoustic signal detection, adapted for use in acoustic velocity well logging to measure the difference in transit times of an acoustic signal between a transmitter and two or more receivers. In a preferred embodiment of the present invention two timing measurements of the signal arriving at each of two receivers may be made by activating zero crossing detectors at the arrival of the first negative and first positive half-cycles at each receiver. A transit time is calculated from the zero crossing times following the first negative half-cycle.

Abstract: A method and apparatus are described for detecting an acoustic wave in a waveform produced from a sonic receiver in response to an acoustic investigation of a borehole. The maximum amplitude of the waveform is measured and a portion thereof utilized as a threshold for comparison with successively different combinations of initial portions of the waveform and the waveform location, where the threshold is exceeded, is identified as the location of the wave. A pattern comparison is made between waveform segments where the acoustic wave is initially located to provide a correction factor for a more accurate locating of the acoustic wave. A parameter of the wave, such as its interval travel time is measured with the acoustic wave locating techniques.

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.