Abstract: An apparatus for evaluating the possibility of casing failure in a borehole measures azimuthal changes in a property responsive to azimuthal changes in axial stress. The measurements may be of acoustic velocity, magnetic permeability, and Barkhausen noise.

Abstract: Acoustic transducers configured with transducer elements disposed on an arch or arcuate shaped member adapted to fit in juxtaposition around a tubular. The arcuate shaped member is adapted with conductors to provide a voltage to the transducer elements. One embodiment uses a metallic arcuate shaped member. Embodiments implemented as sources are used to excite borehole acoustic modes. Some embodiments provide phased array acoustic energy excitation/signal reception. The transducers are covered with a sealer in a liquid-free configuration and shields are used to protect the transducers.

Abstract: A method for hydraulic fracture imaging consistently integrates ground deformation data and microseismic data. A time sequence of hydraulic fracture images is computed from the combined data by first computing an orientation and location of the fracture. A size of the fracture (e.g., length, width, and opening) and detailed shape is then computed consistent with the computed orientation using a stochastic optimization procedure. This procedure may be performed by selecting a candidate model of the fracture consistent with the computed orientation, computing a predicted surface deformation from the candidate model (e.g., using elastic crack theory), computing a predicted seismic activity from the candidate model (e.g., using Dieterich seismicity rate theory), and comparing the predicted surface deformation and predicted seismic activity with the collected ground deformation data and earthquake locations derived from the collected seismic activity data.

Abstract: Fracture- and stress-induced sonic anisotropy is distinguished using a combination of image and sonic logs. Borehole image and sonic logs are acquired via known techniques. Analysis of sonic data from monopole P- and S-waves, monopole Stoneley and cross-dipole shear sonic data in an anisotropic formation are used to estimate at least one compressional and two shear moduli, and the dipole fast shear direction. Fracture analysis of image logs enables determination of fracture types and geometrical properties. Geological and geomechanical analysis from image logs provide a priori discrimination of natural fractures and stress-induced fractures. A forward quantitative model of natural fracture- and stress-induced sonic anisotropy based on the knowledge of fracture properties interpreted from image logs allows the computation of the fast-shear azimuth and the difference in slowness between the fast- and slow-shear. The misfit between predicted and observed sonic measurements (i.e.

Abstract: A longitudinally segmented acoustic transducer for a cement bond logging (CBL) tool having a plurality of adjoining PZT ring-like segments driven synchronously in parallel by one or more pulses and caused to vibrate in an anti-resonant mode, substantially below the resonant frequency of an individual segment when used in a transmitting application. When used in a receiving application, each of the plurality of transducer rings are caused to vibrate by acoustic signals detected by the transducer array, also in an anti-resonant mode. High speed digital signal processing enables on-depth, high quality data for all azimuths at each depth to be obtained, processed, normalized and either sent to the surface in real time for each 20 Hz firing cycle, as the CBL tool is pulled toward the surface, or stored in a memory module in digital form for later retrieval. Built-in calibration factors used for normalizing the output signals to the operating conditions of use may be accessed at any time.

Abstract: A longitudinally segmented acoustic transducer for a cement bond logging (CBL) tool having a plurality of adjoining PZT ring-like segments driven synchronously in parallel by one or more pulses and caused to vibrate in an anti-resonant mode, substantially below the resonant frequency of an individual segment when used in a transmitting application. When used in a receiving application, each of the plurality of transducer rings are caused to vibrate by acoustic signals detected by the transducer array, also in an anti-resonant mode. High speed digital signal processing enables on-depth, high quality data for all azimuths at each depth to be obtained, processed, normalized and either sent to the surface in real time for each 20 Hz firing cycle, as the CBL tool is pulled toward the surface, or stored in a memory module in digital form for later retrieval. Built-in calibration factors used for normalizing the output signals to the operating conditions of use may be accessed at any time.

Abstract: Aspects of this invention include a downhole tool having first and second radially offset ultrasonic standoff sensors and a controller including instructions to determine at least one of a drilling fluid acoustic velocity and a drilling fluid attenuation coefficient from the reflected waveforms received at the standoff sensors. The drilling fluid acoustic velocity may be determined via processing the time delay between arrivals of a predetermined wellbore reflection component at the first and second sensors. The drilling fluid attenuation coefficient may be determined via processing amplitudes of the predetermined wellbore reflection coefficients. The invention advantageously enables the acoustic velocity and attenuation coefficient of drilling fluid in the borehole annulus to be determined in substantially real-time.

Abstract: An apparatus for evaluating a tubular in a borehole of includes at least two electromagnetic acoustic transducers. The transducers are configured to generate and receive first and second acoustic waves in the tubular. A difference in velocity of the two acoustic waves is indicative of a stress field in the tubular.

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: The present invention provides a method and apparatus for using an acoustic logging tool conveyed in a borehole in an earth formation for determining a characteristic of the formation. The method comprises using a first acoustic source for generating an acoustic signal in the earth formation at a first frequency. A second acoustic source spaced apart from the first source is used for generating an acoustic signal in the earth formation at a second frequency different from the first frequency. An acoustic receiver is used for receiving a third acoustic signal indicative of said characteristic. The third acoustic signal has a frequency substantially equal to a difference between the first frequency and the second frequency. The third acoustic signal is produced by a nonlinear interaction between the first signal and the second signal in a portion of said earth formation.

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 downhole tool 10 includes means for detecting a downhole condition, a capacitor bank, and a sparker. The technique is particularly useful for detecting casing collars. As the tool is passed along the well bore 11, it detects collars 12. On each detection, a part of the capacitor bank is discharged through the sparker. This generates an acoustic pulse which is transmitted through the ground (wave 14) to detectors 15, 16. The movement of the tool 10 is also monitored by a movement detector 20. The position of the tool 10 is correlated with the positions of the collars 12 by a computer 22 fed via interfacing circuitry 21. If desired, the pulses may be coded by strength, number, time spacing, etc.

Abstract: A downhole tool for gathering formation data from inside a borehole includes a substantially tubular housing adapted for axial connection to a drill string and multiple sensors coupled to the tubular housing. The sensors include a first pair of sensors aligned along a first axis and adapted to measure a spatial derivative along the first axis, a second pair of sensors aligned along a second axis and adapted to measure a spatial derivative along the second axis, and a third pair of sensors aligned along a third axis and adapted to measure a spatial derivative along the third axis. In selected embodiments, the spatial derivatives are used to differentiate seismic or sonic compression and shear waves measured in a downhole environment.

Abstract: An acoustic detection of a discrete acoustic signal allows to detect a leak behind a casing (23) of a borehole. An acoustic amplitude (AA) is sampled during a recording time period (24; 64) at a determined position along the tube. Time intervals (26; 66) are defined inside of the recording time period (24), and for each time interval (26) the measured acoustic amplitudes are processed to obtain respectively a corresponding power-frequency spectrum (261). A plurality of the power-frequency spectra are analyzed to identify the discrete acoustic signal by detecting time and frequency dependant changes of power. Preferably the processing involves a Fourier transform analysis. A power-frequency time plot is used to conveniently identify the discrete acoustic event.

Abstract: The invention provides methods and apparatus for detecting seismic waves propagating through a subterranean formation surrounding a borehole. In a first embodiment, a sensor module uses the rotation of bogey wheels to extend and retract a sensor package for selective contact and magnetic coupling to casing lining the borehole. In a second embodiment, a sensor module is magnetically coupled to the casing wall during its travel and dragged therealong while maintaining contact therewith. In a third embodiment, a sensor module is interfaced with the borehole environment to detect seismic waves using coupling through liquid in the borehole. Two or more of the above embodiments may be combined within a single sensor array to provide a resulting seismic survey combining the optimum of the outputs of each embodiment into a single data set.

Abstract: A power supply apparatus is provided for supplying power and communications within a first piping structure. An external power transfer device is positioned around the first piping structure and is magnetically coupled to an internal power transfer device. The internal power transfer device is positioned around a second piping structure disposed within the first piping structure. A main surface current flowing on the first piping structure induces a first surface current within the external power transfer device. The first surface current causes a second surface current to be induced within the internal power transfer device.

Abstract: The invention provides a method for estimating an impedance of a material behind a casing wall, wherein the casing is disposed in a borehole drilled in a geological formation, and wherein a borehole fluid is filling said casing, the material being disposed in an annulus between said casing and said geological formation, said method using a logging tool positionable inside the casing and said method comprising: exciting a first acoustic wave in said casing by insonifying said casing with a first pulse, the first acoustic wave having a first mode that may be one of flexural mode or extensional mode; receiving one or more echoes from said first acoustic wave, and producing a first signal; extracting from said first signal a first equation with two acoustic properties unknowns for respectively said material and said borehole fluid; exciting a second acoustic wave in said casing by insonifying said casing with a second pulse, the second acoustic wave having a thickness mode; receiving one or more echoes from said

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 of producing images of formations surrounding a borehole, comprises: obtaining values of a first parameter in the borehole as a function of depth and azimuth at a first resolution; obtaining values of a second parameter in the borehole as a function of depth only at a second resolution; establishing a relationship between the first and second parameters at a matched resolution; using the relationship to derive values of the second parameter as a function of depth and azimuth; and producing an image of the second parameter as a function of depth and azimuth using the derived values of the second parameter.

Abstract: The invention provides methods and apparatus for detecting seismic waves propagating through a subterranean formation surrounding a borehole. In a first embodiment, a sensor module uses the rotation of bogey wheels to extend and retract a sensor package for selective contact and magnetic coupling to casing lining the borehole. In a second embodiment, a sensor module is magnetically coupled to the casing wall during its travel and dragged therealong while maintaining contact therewith. In a third embodiment, a sensor module is interfaced with the borehole environment to detect seismic waves using coupling through liquid in the borehole. Two or more of the above embodiments may be combined within a single sensor array to provide a resulting seismic survey combining the optimum of the outputs of each embodiment into a single data set.

Abstract: Fiber optic cables suitable for use in harsh environments such as down hole oil and gas well applications and methods for fabricating the same have been provided. In one embodiment, an optic cable suitable for down hole oil field applications comprises one or more optical fibers disposed in an inner tube and a corrosion resistant metal outer tube disposed over the inner tube, where the inner and outer tubes make intermittent contact. In another embodiment, an optic cable suitable for down hole oil field applications comprise one or more optical fibers disposed in a polymer tube having fins extending therefrom.

Abstract: A method for predicting the location of stress corrosion cracking in a steel gas pipeline in which in-line stress corrosion cracking smart tool data, external low level metal loss data and soil characterization data are compiled to predict the location of stress corrosion cracking in a steel gas pipeline segment.

Abstract: A casing sensor and methods for sensing using a casing sensor are disclosed. The casing sensor includes a casing shoe and a sensor coupled to the casing shoe. A casing data relay includes a downhole receiver coupled to a well casing and a transmitter coupled to the receiver. The casing sensor may be coupled to the transmitter. A drill string actuator may be controllable through the downhole receiver.

Abstract: Methods and apparatus for suppression of wave energy within a fluid-filled borehole using a low pressure acoustic barrier. In one embodiment, a flexible diaphragm type device is configured as an open bottomed tubular structure for disposition in a borehole to be filled with a gas to create a barrier to wave energy, including tube waves. In another embodiment, an expandable umbrella type device is used to define a chamber in which a gas is disposed. In yet another embodiment, a reverse acting bladder type device is suspended in the borehole. Due to its reverse acting properties, the bladder expands when internal pressure is reduced, and the reverse acting bladder device extends across the borehole to provide a low pressure wave energy barrier.

Abstract: Methods for processing ultrasonic signal data to evaluate subsurface properties and tool orientation. Acoustic signals are transmitted into a plurality of azimuthal borehole positions. Formation echo signal transit time distributions are then determined in a plurality of azimuthal sectors for the acoustic signals. Front face echo signal transit times are also measured and farther-mode and closer-mode transit times are determined for the distribution of formation echo signals. Farther and closer tool standoffs are determined for the azimuthal sectors and a borehole diameter is determined from a summation including standoffs in opposing sectors. The standoffs are also used to determine a preferential tool position.

Abstract: A method and device are shown for detecting the characteristics of a cement annulus between a casing in a borehole and the surrounding earth formations in a slickline cement bond logging operation. An acoustic logging tool is utilized which produces a pure signal downhole. The received acoustically transmitted energy produces electrical signals indicative of both the amplitude of the received energy and variable density log data. Both the amplitude data and the variable density log data are captured in memory downhole by the use of a time amplitude matrix which stores a limited number of data points for producing a cement bond log at the well surface.

Abstract: Improved methods and apparatuses for directly monitoring well casing strain and structural integrity are disclosed that allows for monitoring of potentially damaging strain from any orientation or mode and over long stretches of well casing. In a preferred embodiment, optical fiber sensors are housed within a housing and attached to the exterior surface of the casing. The sensors may be aligned parallel, perpendicular, or at an appropriate angle to the axis of the casing to detect axial, hoop, and shear stresses respectively. The sensors are preferably interferometrically interrogatable and are capable of measuring both static and dynamic strains such as those emitted from microfractures in the well casing. Analysis of microfracture-induced acoustics includes techniques for assessment of relatively high frequencies indicative of the presence of microfractures.

Abstract: A method and apparatus for isolating a seismic sensor module from high-g shock loads such as those encountered during handling, deployment and retrieval of the module. The sensor module includes one or more MEMS accelerometers in an electronics package. The electronics package is housed within a module case. And one or more isolators are disposed between the electronics package and the module case to provide shock isolation.

Abstract: A casing sensor and methods for sensing using a casing sensor are disclosed. The casing sensor includes a casing shoe and a sensor coupled to the casing shoe. A casing data relay includes a downhole receiver coupled to a well casing and a transmitter coupled to the receiver. The casing sensor may be coupled to the transmitter. A drill string actuator may be controllable through the downhole receiver.

Abstract: In an apparatus and method for actuating arms used on a borehole data-logging tool to deploy measuring instruments against a borehole wall, a mandrel is provided. At least one arm carried by the mandrel is mounted to the mandrel to move between an expanded position, in which a part of the arm projects from the mandrel, and a retracted position. A resilient biassing compression spring provides a resilient biassing force on each arm for biassing the arm towards its expanded position. A hydraulic piston and cylinder assembly associated with each arm restrains the arm against movement towards its expanded position. A drive piston and cylinder assembly acts upon the resilient biassing compression springs for adjusting the resilient biassing force acting upon each arm.

Abstract: Methods and equipment are described for placement of an array of seismic sensor sets along a horizontal section of wellbore for monitoring microseismic activity during and after hydro-fracturing. A perforated wellbore liner is positioned in the horizontal wellbore production section with sonic transmission enhancement devices such as longitudinal blade centralizers for acoustically coupling seismic sensing devices to the production formation. Internally of the perforated liner, a coiled tube is placed having an array of signal cable connected seismic sensor sets. The seismic sensor sets are linked to the coiled tube wall by sonic transmission enhancement devices and the tube wall linked by acoustic transmission enhancement devices to the perforated liner.

Abstract: This invention relates to mapping the hydrocarbon reservoir characteristics by mapping the reservoir formations that display dynamic elastic nonlinearity responses to the seismic signals. The main reason of this nonlinear behavior in the reservoir rocks is their bulk rock property: the porosity, fractures, differential pressure and pore saturation. To map these bulk rock properties, the interaction of the two seismic waves as they propagate through elastically nonlinear rocks is recorded. Two compressional seismic signals are transmitted from the surface. Seismic reflection data using surface or borehole detectors are recorded. One of the transmitted signals is a conventional swept frequency and the other is a mono-frequency signal. During the propagation of these two signals through the elastically nonlinear reservoir rocks, there is an interaction between the two signals. The sum and difference frequencies of the two primary seismic signals that were transmitted from the surface are created.

Abstract: A method for determining properties of a transverse isotropic region of earth formations traversed by a wellbore having substantially vertical and deviated sections therethrough, including measuring sonic velocity properties in formations surrounding the substantially vertical section of the wellbore; measuring sonic velocity properties in formations surrounding the deviated section of the wellbore; and determining, from the measured velocities, all of the transverse isotropic elastic constants of the region.

Abstract: A method and apparatus for determining acoustic mud velocity and bore hole caliper in a downhole environment. A highly accurate acoustic signal is adjusted for mud velocity as continuously measured. The borehole standoff is utilized to compensated data collected downhole in determining a parameter of interest in the wellbore or an adjacent formation.

Abstract: An acoustic MWD system comprises at least one transmitter array and at least one receiver array spaced axially along an essentially tubular downhole subassembly. Each transmitter and receiver array includes a plurality of elements circumferentially disposed on the outside of the assembly. The downhole subassembly also comprises a processor, data storage, telemetry elements, power supplies and control circuits as well as other types of sensors. In one embodiment of the invention, the transmitters are operated as a quadrupole in orthogonal orientations and signals from two receiver elements processed to attenuate common modes (including body waves through the tool, monopole waves and Stoneley waves). In another embodiment, the transmitters are used as crossed dipoles and signals received by cross-dipole receivers may be used to determine shear wave birefringence in the formation.

Abstract: A method and device are shown for detecting the characteristics of a cement annulus between a casing in a borehole and the surrounding earth formations in a slickline cement bond logging operation. An acoustic logging tool is utilized which produces a pure signal downhole. The received acoustically transmitted energy produces electrical signals indicative of both the amplitude of the received energy and variable density log data. Both the amplitude data and the variable density log data are captured in memory downhole by the use of a time amplitude matrix which stores a limited number of data points for producing a cement bond log at the well surface.

Abstract: A method and apparatus for measuring the properties, such as permeability, of the rock surrounding a metal cased borehole by generating a seismic or sonic shock downhole within the borehole which is propagated into the surrounding formation where it generates an electrokinetic signal which is detected by measuring the potential between at least two space apart electrodes in contact with the casing.

Abstract: A borehole tool including a tool body having and an anchoring mechanism, the anchoring mechanism having a drive mechanism including a motor, drive shaft, and clutch; an anchor arm moveable between first and second positions relative to the tool body; a push rod connecting the anchor arm to the drive mechanism; and a spring acting to bias the arm into a first position relative to the tool body. The push rod extends through the clutch mechanism and is engaged by the spring to bias the arm into the first position, and is also driven by the drive mechanism through the clutch to move the arm between the first and second position. The push rod may be connected to the anchor arm by a link. Measurement devices may be used to determine the position of the anchor arm or the tool body.

Abstract: A method and system for diagnosing surface imperfections of an article is provided. A data collection system collects data relating to the surface of the article, and a processor operatively coupled to the data collection system analyzes the surface data to determine deviations in the surface corresponding to surface imperfections and pre-made surface interruptions, and distinguishes between the imperfections and interruptions.

Abstract: The acoustic impedance of a fluid in a borehole is determined 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 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. The sonic velocity of the fluid is also measured and, when combined with the acoustic impedance, is used to determine fluid density.

Abstract: An acoustic system and method for monitoring a hydrocarbon reservoir. Wellbore tube wave energy may be created by natural or ambient sources or tube waves may be excited intentionally. Wellbore tube wave energy is converted to seismic body wave energy at minor borehole obstructions or irregularities. Each obstruction or discontinuity position along the borehole has an associated unique waveform source coda that may be measured for processing the body waves radiated into the earth formation surrounding the well bore. A plurality of sensors detects the radiated seismic energy after the seismic body wave energy has transited intervening earth formations. The system may be employed for permanent monitoring of mineral resources and resource management. Measurements of reservoir characteristics may be acquired at many different times over the productive life of a reservoir.

Abstract: A method for detecting a leak in a well tubular of a well for production of hydrocarbon fluid from a formation is disclosed. The method includes steps of: passing a sonic tool provided with a transducer package capable of sending and receiving a sonic signal through the well tubular; prior to starting production to obtain an initial registration of a reflected signal for a well that does not have a leak; obtaining at least one subsequent registrations of reflected signals; comparing the initial registration to a subsequent registration and determining from the differences between the two if a leak has developed in the well tuburtar.

Abstract: A method and apparatus for utilizing flexural excitations to characterize and/or image a cased well is disclosed. Various applications of the method and apparatus are also discussed.

Abstract: The present invention relates to analysis tools for analyzing the ground 1, from a surface 2 thereof, by means of a sonde 3 having a given analysis lobe 4 and a resolution time T. The tool of the invention is essentially characterized by the fact that it comprises a drive head 10 driven to move in continuous translation at a speed V relative to the surface 2 and along a direction 11 parallel to the surface 2, a skid 12, means 13 for associating the sonde 3 and the skid 12 so that the sonde can analyze the rocks contained in its lobe 4, and means 14 for coupling together the drive head 10 and the skid 12 so that the two elements can be displaced relative to each other along the direction 11 over a distance D. The tool of the invention finds a particularly advantageous application in analyzing oil-bearing rocks surrounding the wall 30 of an oil well 31, in order to determine both the distribution of the porosity of the rocks, and their associated permeability.

Abstract: The present invention is a method of estimating formation properties by analyzing acoustic waves that are emitted from and received by a bottom hole assembly.

Abstract: An ultrasonic sensor assembly for measuring the diameter of a well while it is being drilled is provided. The sensor assembly includes a stack including an inner sound absorbing backing element, a piezoelectric ceramic disk transducer stacked outwardly adjacent the backing element, and a matching layer, preferable made of PEEK and disposed outwardly adjacent the transducer. The layers of the stack are provided within a cavity of a metal cup and are maintained in position by a flexible diaphragm preferably made of PEEK. The diaphragm is sealed with an O-ring. A window, also preferably made of PEEK, is provided against the diaphragm and is held against the diaphragm by a spring. This arrangement acoustically couples the diaphragm to the stack and improves signal recovery. The diaphragm and O-ring form a hydraulic seal between fluid/mud in the well and the stack, and operate to retain the layers of the stack.

Abstract: A borehole tool, such as a seismic shuttle-type logging tool, including a tool body having at least one sensor package and an anchoring mechanism, the anchoring mechanism having a drive mechanism including a motor, a drive shaft and a clutch; an anchoring arm moveable between first (extended)and second (retracted) positions relative to the tool body; a push rod connecting the anchoring arm to the drive mechanism; and a spring acting to bias the arm into a first position relative to the tool body. The push rod extends through the clutch mechanism and is engaged by the spring to bias the arm into the first position, and is also driven by the drive mechanism through the clutch to move the arm between the first and second positions. The spring is a coil spring surrounding the drive mechanism and acting on the push rod directly.

Abstract: The invention relates to an ultrasonic measuring instrument comprising a housing which contains a transducer for transmitting and receiving ultra-sound waves, and a rotatable mirror placed inside the housing for directing ultra-sound waves coming from the transducer through a tapering window comprised in the housing to an object of measuring outside the housing, and for directing ultra-sound waves which are reflected by the object of measuring and which enter the housing through the window to the transducer. Around, and rotating with the mirror a tube is provided, comprising a recess for the passage of ultra-sound waves.

Abstract: Apparatus and method for measuring the properties of rocks such as permeability, porosity and fluid properties downhole around a borehole (3) in which a seismic source (6) which radiates a seismic signal substantially radially within the borehole is lowered down the borehole (3) and the electrical signal generated by the seismic signal within the surrounding rock is detected by detectors (4, 5) mounted above and below the seismic source (6) so that signals are received from substantially all radial directions. Preferably a continuous wave signal is generated and the signal detected whilst the apparatus (1) is raised or lowered. The apparatus (1) gives a much better and more accurate measurement than previous methods.

Abstract: A transducer is described especially for use in providing acoustic transmission in a borehole. The transducer includes a multiple number of magnetic circuit gaps and electrical windings that have been found to provide the power necessary for acoustic operation in borehole while still meeting the stringent dimensional criteria necessitated by boreholes. Various embodiments conforming to the design are described. Moreover, the invention includes transition and reflector sections, as well as a directional coupler and resonator arrangement particularly adapted for borehole acoustic communication.