Abstract: A method of use of a logging tool (1) including a directional emission device (4) and/or reception device (R1, R2) and the achieving of several series of loggings while modifying between each series the orientation of the directivity diagrams. At least one first series is performed by orienting the directivity diagrams towards the top or the wall of a reservoir zone crossed through by the well bore, for example. At least one second series is carried out by orienting the directivity diagrams towards the opposite direction, for example. The recordings are then combined, and the reflected arrivals, which are generally concealed by casing waves, can be easily seen. This facilitates the locating of further discontinuities. The directional selectivity of the emissions and/or the receptions is, for example, obtained by positioning a cover fitted with a window (5) around emitting and/or receiving transducers. The method can be applied to loggings in horizontal well bores, for example.

Abstract: A seismic directional sensor for solid-borne sound has at least one geophone with pronounced directional characteristic. The measuring electrical vibration signals, which are obtained at different circumferential angular positions of the radial longitudinal axis of the geophone and are to be compared with one another, are correlated with the direction of a seismic ray extending at right angles to the longitudinal axis of the geophone, which is ineffective in its neural circumferential angular position.The neutral circumferential angular position is determined by the ratio of the amplitude of the measuring signals which are determined on both sides adjacent to the neutral circumferential angular position in effective circumferential angular positions of the geophone. The vibration pattern of the measuring signals is antiphase in relation to the respective other side.

Abstract: A device and method for suppressing acoustic tube wave noise in a borehole. The device comprises an absorptive material that is positioned in a borehole so that the device will encounter and absorb the tube waves before the waves are detected by receivers. The device can also contain a housing in which to place the absorptive material. The housing can also be surrounded by an absorptive material to help absorb energy reflecting off the borehole wall.

Abstract: A borehole logging tool having a dipole acoustic energy source and at least one spaced-apart dipole acoustic energy receiver is lowered into a deviated borehole. A motor rotates the source and receiver about the axis of the borehole tool. A first signal is produced representing source and receiver rotational position relative to rotational position of the borehole tool. A second signal is produced representing rotational position of the borehole tool relative to a vertical direction. A comparator produces a third signal of the difference between the first and second signals as a representation of source and receiver rotational position relative to the vertical direction. The motor rotates so as to minimize such third signal, thereby rotating the focus of the source and receiver in a direction perpendicular to the eccentricity of the borehole tool in the deviated borehole.

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: Apparatus is provided for acoustically logging earth formations surrounding a borehole containing a known fluid, and includes a downhole tool adapted for longitudinal movement through the borehole, an acoustic transducer assembly for transmitting and receiving acoustic pulse energy, and extendable arms mounting the acoustic transducer assembly on the tool and adapted for lateral extension therefrom for positioning the acoustic transducer assembly in contact with the borehole wall. The acoustic transducer assembly further includes acoustic transducer means for generating acoustic pulse energy for coupling into the borehole fluid substantially free of acoustic ringing and directed an axis generally normal to the borehole wall surface.

Abstract: A method and apparatus for detecting the orientation of downhole geophones are provided. A gamma ray source is secured to a casing enclosing a geophone such that the location of the gamma ray source with respect to the orientation of a geophone is known. The geophone is secured to tubing such that the orientation of the geophone with respect to the tubing is known. The tubing, with attached geophone, is secured downhole. A gamma ray logging tool is run the length of the tubing. The orientation of the downhole geophone is determined from the gamma ray log.

Abstract: A drill string in a fluid-filled borehole acts as a waveguide for an extensional wavefield that is generated in the drill string when it is excited by the vibrations of a drill bit secured to the lower end of the drill string. The waveguide acts as a distributed acoustic energy source which initiates head waves in the surrounding formation. The head waves are detected at one or more discrete locations near the surface of the earth. The extensional wavefield is detected by a sensing means mounted at the top of the drill string. The detected head waves are cross-correlated with the detected extensional waves to create a cross-correlogram which may be displayed.

Abstract: A pack-off locking means for use in downhole geological seismic work. An upper and lower endcap rigidly connected together by a inelastic vertical member which is adapted to hold a seismic energy source. The endcaps have sealing means attached thereto for isolating a cylindrical section of the well borehole, thus, forming a sealed chamber wherein the seismic energy source contained therein transmits acoustical energy in a mostly horizontal and omni-directional plane into geological formations of interest. Minimal acoustical energy is transmitted into the borehole vertical fluid column because the seal-off means prevents communication thereto. Means for pressurizing the chamber formed by the pack-off means and for measuring the pressure thereof.

Abstract: A downhole seismic shear wave source is used to generate seismic shear waves a downhole environment. At least one double headed piston rod with a third piston on the center of the rod slides laterally in the downhole tool. Each end piston head is connected to a rolling diaphragm that is secured at its edges around the periphery of the piston receiving cavity. The cavity is filled with a low viscosity non-conducting oil. A servovalve is connected to opposite sides of the center piston head to produce low frequency vibration of the source generator. A veed target rod extends between the end piston heads, past a pair of eddy current transducers (ECTs) to monitor movement of the generator and provide feedback control to the servovalve. A second downhole seismic shear wave source contains a continuous vibrator ring replaces the diaphragm/oil system and a linear variable differential transformer (LVDT) replaces the eddy current transducers as the feedback signal generator.

Abstract: A method and apparatus for inter-well seismic logging include a seismic source capable of being lowered into a first or surce well and a plurality of receiving and/or detecting means capable of being lowered to at least one second or receiving well. Signals generated from the seismic source pass through the earth and are received by the respective receivers. The recorded data is subsequently computer processed to form a profile which represents the geological configuration between the wells. The seismic source having at least one bender arm assembly including two sets of piezoelectric ceramic crystals and, preferably, a reaction mass connected intermediate the ends thereafter generate the seismic signals.

Abstract: A sonic well tool includes a transmitter array, including at least one monopole transmitter and at least one dipole transmitter, and a receiver array for receiving sonic pressure wave signals from a surrounding borehole formation. A first attenuation and delay apparatus is positioned above the receiver array and a second attenuation and delay apparatus is positioned below the receiver array in the sonic well tool. The first attenuation and delay apparatus includes an attenuation member comprising a plurality of interleaved rubber and metal like washers for attenuating compressional and flexural waves propagating along a metal, center support rod to the receiver array and an inner housing comprising a bellows section having a corrugated shape and a thin transverse dimension for delaying the propagation of compressional and flexural waves along the inner housing to the receiver array.

Abstract: The quadrupole shear wave logging device of this invention includes a logging sonde, means for generating a quadrupole shear wave in the earth formation surrounding a borehole containing fluid, and means for detecting in the fluid the refraction of the quadrupole shear wave. In the preferred embodiment, the generating means comprises four similar sectors of a hollow piezoelectric cylinder. The four cylinders are polarized radially. The four sectors are so connected to the sonde that they are in the form of a split cylinder coaxial with the sonde axis. Electrical pulses of similar waveforms are applied across the inner and outer cylindrical surfaces of each sector to vibrate the four sectors. The electrical pulses are of such polarities that, during their initial motions of vibration, two oppositely situated sectors are caused to move outward and the remaining two oppositely situated sectors to move inward substantially simultaneously.

Abstract: Method and apparatus for applying the measuring pads of a logging sonde against the walls of a borehole. Dip measurements and geological investigation of earth formations traversed by a deviated borehole require that the measuring pads be pressed against the borehole walls by means of articulated arms which maintain the pads symmetrical and parallel with respect to the sonde. In the preferred embodiment, two independent resilient forces are applied to the pads. The first resilient force is substantially constant at all extensions of the arms in the borehole, while the second resilient force is adjustable to suit local parameters. The second resilient force is preferably adjustable from surface instrumentation while the sonde is making measurements in the borehole. The first resilient force is provided by independent leaf springs acting on each of the pads, while the second resilient force is preferably provided by a coil spring acting on each of the pairs of opposing arms.

Abstract: A method and device are disclosed particularly adapted for seismic prospection in substantially horizontal drains using intermediate frequency acoustic waves for conciliating the range and the power of resolution. In a well is lowered steps-by-steps a transmission-reception assembly comprising at least one probe associated with a guide block but able to be mechanically uncoupled therefrom, and at least one acoustic wave source associated with a guide block. The source is inserted in a rigid column connecting the probe to the surface control device. A delayed connection system makes it possible to connect the probe and the source electrically to a surface control and recording assembly. The source comprises one or more vibrators transmitting in the 200-2000 Hz band for example or a sparker.

Abstract: A logging tool is lowered in a borehole. The tool is positioned so that the transducer is offset from the axis of the borehole. The transducer transmits acoustic energy such that it strikes the borehole wall or casing at an incident angle that directs reflections from the borehole wall away from the transducer and at the same time allows transmission into the surrounding formations or cement in the borehole annulas between the casing and the borehole wall. Reflections of the transmitted acoustic energy from anomalies within the surrounding formations as well as cement in the annulas are received by the transducer.

Abstract: An acoustic logging system for detecting anomalies in formations surrounding a borehole. The system can be used for evaluating the formation for fractures or the bond between a well casing and the cement used to seal the space between the casing and the formation. The system utilizes at least one rotating acoustical transmitter/receiver and at least one receiver vertically spaced from the rotating transducer. The signals from both receivers are analyzed to detect the presence of anomalies, such as fractures or voids in a cement bond.

Abstract: The shear velocity of a region of an earth formation may be determined by a logging tool insertable in a wellbore penetrating the formation which includes plural transducers for generating compressional waves for transmission through the formation as shear wave between the signal generating transducers and an array of signal receiving transducers spaced from the signal generating transducers. The transducers may be plural in number and arranged to effect impingement of the compressional wave on the borehole wall at an angle of incidence preferably in the range of 35.degree. to 75.degree. to a normal to the wall surface. The transducer array is controlled so that a significant portion of the compressional wave energy transmitted through liquid in the wellbore is converted to shear waves at the wellbore wall, which shear waves constructively interfere to develop a torsional wave propagating along the wellbore between the transducers and the receiver elements.

Abstract: A method and apparatus for remotely determining the profile of an inaccessible subterranean passage for example in a mine. An instrument pod is moved through the passage in steps. At each step, a rangefinder scans the wall of the passage and provides to a remote monitor, range measurements from which a profile can be determined. The pod also carries clinometers for determining the orientation of the pod during each profile measurement. The pod also carries a television camera and lights so that the wall of the passage can be visually inspected.

Abstract: The quadrupole shear wave logging device of this invention includes a logging sonde, means for generating a quadrupole shear wave in the earth formation surrounding a borehole containing fluid, and means for detecting in the fluid the refraction of the quadrupole shear wave. In the preferred embodiment, the generating means comprises four similar sectors of a hollow piezoelectric cylinder. The four cylinders are polarized radially. The four sectors are so connected to the sonde that they are in the form of a split cylinder coaxial with the sonde axis. Electrical pulses of similar waveforms are applied across the inner and outer cylindrical surfaces of each sector to vibrate the four sectors. The electrical pulses are of such polarities that, during their initial motions of vibration, two oppositely situated sectors are caused to move outward and the remaining two oppositely situated sectors to move inward substantially simultaneously.

Abstract: A method and apparatus are disclosed for measurement of earth formation dip utilizing sonic techniques. At least three electroacoustic devices are utilized, each having an electroacoustic transmitter and a pair of electroacoustic receivers. The electroacoustic receivers are both located on one side of the transmitter and are preferably located vertically adjacent along a line with the transmitter. Transmitted acoustic energy is detected by the receivers and the elapsed time between detection by a first receiver and detection by a second receiver is determined. A correlation of the variations in elapsed times for each of the three electroacoustic devices is then utilized to calculate the formation dip at various depths.

Abstract: The process consists in generating a primary tube wave, in using a reflecting element for the tube wave and in recording the times of emission of the induced waves radiated by the reflecting element, in receiving and recording at least part of the induced waves, then in processing the recorded signals so as to determine the characteristics of the medium to be explored. Application in particular to exploration between boreholes.

Abstract: An acoustic borehole well logging method and apparatus for measuring azimuthal anisotropy of a formation traversed by a borehole using at least one multipole transducer. In a preferred embodiment, a dipole wave transmitter and at least one detector sensitive to dipole waves are employed. In an alternative preferred embodiment, a monopole transmitter and at least one multipole detector are employed. In the inventive method, two acoustic wave arrivals are detected, each associated with a different azimuthal orientation relative to the longitudinal axis of the borehole (i.e. each is transmitted by a multipole transmitter oriented at such angle, or is detected by a multipole detector oriented at such angle, or both). The inventive apparatus preferably includes at least one transducer unit including two or more multipole transmitters (or two or more multipole detectors) oriented at different azimuthal angles relative to the tool's longitudinal axis.

Abstract: A suspended structure for coupling a seismic source to the walls of a borehole, in particular for underground prospecting purposes, the structure comprising top (14) and bottom (16) elongate plug elements having transverse dimensions substantially equal to the inside dimensions of the borehole (10), defining therebetween a substantially closed space (32), and suspension elements (30, 50) connecting the bottom plug element to the top plug element without isolating said space from the surrounding walls of the borehole, a seismic source (34) suitable for acting in said space, with the top and bottom plug elements opposing said action in the longitudinal direction of the borehole so that said action is applied essentially against the walls (10) of the borehole level with said space.Applicable to underground prospecting together with pick-up means.

Abstract: For seismic exploration, a method and apparatus are set forth wherein geophones, preferably arranged in XYZ relationship to one another fixedly within a hermetically sealed housing, are located in a deviated well. The position of the housing with respect to a reference such as the earth's north axis is determined. This reference enables determination of the geophone location and the direction of propagation of seismic impulse.

Abstract: A seismic exploration method and system employing a streamer that houses at least one pair of orthogonally mounted hydrophones. The streamer may be operated downhole in a well, or may be towed in a body of water by a marine vessel. In the downhole embodiment, the invention permits detection of seismic signals of interest with suppression of noise due to tube waves and (dipole and monopole) modal waves propagating in and along the well, and without the need for locking the seismic detectors to the wall of the well. In the marine embodiment, the invention permits selective detection of waves incident from any incidence direction of interest (including the horizontal and vertical directions). In all embodiments, the incidence angle of the detected seismic wave is determined. The amplitude of the detected wave may also be determined from the incidence angle and the amplitude components detected at each hydrophone.

Abstract: A method and system for acoustic well logging for obtaining an indirect measure of shear wave velocities for earth formations surrounding a well borehole. The method and system relate to an indirect technique for inverting Stoneley wave velocity data to obtain an estimate of shear wave velocities of formations surrounding the borehole substantially concurrent with the logging operation. A subassembly adapted to be connected to an acoustic well logging sonde and form a part thereof provides measures of fluid density and velocity, and borehole radius as well as formation density and impedance. By combining the output of the well logging sonde and subassembly with the aid of a processor, one is able to obtain a measure of formation shear wave velocities, by constraining the inversion of measured Stoneley wave velocity data, substantially in real-time. This method is especially useful in slow formations where direct shear wave velocities cannot be obtained or where shear wave velocities are difficult to obtain.

Abstract: The subsurface position of a blowing well with respect to an adjacent relief well is determined by detecting at a plurality of axially and tangentially spaced locations in the relief well acoustic waves emanating from a subsurface location of the blowing well. The distance between the wells is calculated on the basis of the difference in times of arrival of the waves at said axially spaced locations. The radial direction of the blowing well relative to the relief well is determined by measuring the acoustic intensity resulting from the waves at each of said tangentially spaced locations.

Abstract: A spark discharge acoustic pulse transducer for borehole operation provides an insulating ceramic barrier which contains a small cross-section aperture separating two bodies of electrolyte through which the two zones of liquid make contact. An electrical arc discharge is caused to occur through the aperture to produce a transient pressure pulse and associated acoustic pulse which is coupled to the geologic formation at the borehole wall. The specific shape and geometry of the aperture channel in the insulating barrier being exponentially shaped provides a means for controlling the waveform and frequency spectrum of the acoustic pulse. The transducer has an elastic outer housing and an elastic inner housing with hydraulic fluid between the inner and outer housings. The pressure of the hydraulic fluid may be increased to expand the outer housing against a borehold prior to a spark discharge. The transducer is also provided with a system for venting gas produced as a result of the spark discharge.

Abstract: The shear velocity of a formation traversed by a fluid-filled open or cased borehole is obtained directly. Waveforms are obtained from a dipole acoustic investigation of the formation relative to a common location in the borehole. In this investigation, the bandwidth of the waveforms is substantially bounded by an upper frequency f.sub.u at and below which energy traveling at the shear velocity is dominant. Moreover, the bandwidth of the waveforms is concentrated near the frequency f.sub.u. The shear velocity of said earth formation is determined from these waveforms. In one embodiment, the waveforms are obtained from a broadband dipole acoustic investigation. The waveforms are low-pass filtered, and an interim shear velocity v.sub.s is determined from the filtered waveforms. The filtering and determining of v.sub.s are done first for an initial f.sub.cut, and subsequently for additional decreasing values of f.sub.cut, until a preselected relationship between f.sub.cut and v.sub.s is satisfied.

Abstract: An acoustic logging apparatus and method are disclosed for determining the direction of a subsurface noise source, such as a blowout well or fluid channeling behind well casing. The apparatus comprises cylindrical piezoelectric crystal transducers processed to buck each other. The method employs such an apparatus and includes generating and observing output from the crystals. The direction of the noise relative to the position of the apparatus is indicated by determining the position of the crystal transducers when their phase and amplitude differences are at a minimum. The transducer leading in phase at a point perpendicular to said position is the transducer closest to the noise source and is used to indicate the absolute direction of the noise.

Abstract: The shear velocity of a formation traversed by a fluid-filled borehole is determined in the presence of a significant flexural mode arrival. A plurality of waveforms are obtained from a dipole acoustic investigation of the formation relative to a common location in the borehole. The flexural mode phase velocity as a function of frequency is determined. If a low frequency asymptote is identifiable, it is reported as the shear velocity. If a low frequency asymptote is not identifiable, however, a plurality of additional curves of the flexural mode phase velocity as a function of frequency are theoretically determined, based on respective estimated shear velocities. These theoretically determined curves are respectively fitted to the curve determined from the waveforms, until a satisfactory least error fit is achieved. The last-estimated shear velocity is reported as the shear velocity of the formation.

Abstract: Subterranean surveying apparatus includes a support portion, a connector portion, a housing portion, a positioning portion, a monitoring portion and a control portion. The support portion includes a horizontal reference surface and a base section extending downwardly from the reference surface with mechanism for leveling the reference surface. The connector portion includes a torsionally rigid mast assembly suspended from the reference surface and extending downwardly therefrom with mechanism for selectively fixing the position of the mast assembly with respect to the reference surface. The mast assembly includes a plurality of elongated members disposed in an end to end relationship, the elongated members including end sections securable to adjoining ends of other elongated members. The housing portion includes an elongated hollow section, the upper end of which is affixed to the lower end of the mast assembly. At least one opening in the hollow section is intermediate the ends thereof.

Abstract: A logging method and apparatus are provided for the acoustic inspection of a borehole fitted with a casing wherein obtained measurements which are representative respectively of one or more data items relating to the casing and to the material which surrounds it are corrected for the effects of the environment.

Abstract: In the apparatus and method of the invention, acoustic energy is propagated in two slightly differing, or offset, circumferential paths in such a way as to interact with the formation under investigation. The propagating energy is detected and the resulting waveforms are compared using semblance. The waveforms corresponding to the respective paths will be quite similar provided that the length of the paths are equal and that there are no fractures or other similar anomalies between the source and receiver. The waveforms for the respective paths will be quite dissimilar, however, if a fracture or similar anomaly does lie between the source and receiver for the respective paths. The semblance may be displayed in log format.

Abstract: An ultrasonic transducer comprises a cylindrical housing embedded within a rear bumper of a vehicle and opening backward, a reflecting plate having a parabolic reflecting surface provided within the cylindrical housing along a closed end thereof and facing an open end thereof, and an ultrasonic vibrator provided in an upper wall of the housing at the focus of the reflecting plate for emitting and receiving ultrasonic waves. The ultrasonic transducer transmits ultrasonic waves behind the vehicle and receives ultrasonic waves reflected from an obstacle. The ultrasonic transducer further comprises a projecting member provided on the inner wall of the housing along the open end thereof for dispersing and cancelling the ultrasonic waves entering the housing at angles with respect to the axis of the housing. The projecting member has a smoothly curving cross section having a radius of substantially one fourth to five times the wavelength of the ultrasonic waves emitted by the ultrasonic vibrator.

Abstract: The preferred embodiment of this invention includes a logging sonde, an elongated pair of oppositely polarized piezoelectric plates connected to each other by their flat surfaces, and an electrical pulse applying means for applying electrical pulses across the pair of plates so as to bend and vibrate the plates in a direction perpendicular to the length of the plates. Vibration of the plates in a fluid contained in a well creates in the fluid a positive compressional wave in one direction and simultaneously a negative compressional wave in the opposite direction. The two compressional waves will interfere to produce a dipole shear wave in the earth surrounding the well. The dipole shear wave arrival is detected at two locations in the fluid spaced longitudinally along the well from each other and from the plate.

Abstract: For use in an acoustic logging tool having a sonde adapted to be lowered in a borehole, an improved acoustic transducer comprising a pyramidal frustrum is disclosed. The preferred embodiment incorporates fifteen sides. Each side mounts a piezoelectric crystal for receiving. Mechanical resonant frequencies of the transducer are outside the receiver band width which is about 25 kHz. The resonant frequencies are above 25 kHz, thereby avoiding primary resonant frequencies within the band width.

Abstract: The present invention relates to the acquisition of seismic signals at different levels in a borehole, in response to the generation of seismic waves by a source placed on the surface or in the vicinity of the surface. The acquisition is carried out by means of a sonde suspended in the borehole from a cable and equipped with an anchoring pad. At each acquisition level, the pad is anchored in the borehole wall to couple the sonde to the formation, and then the pad is released from the wall once the acquisition is over. The signals acquired are then sent to the surface by means of the cable. The force with which the pad is anchored in the wall is controlled by means of a feedback arrangement which includes a sensor arranged in the pad itself. During the sonde movements from one level to another, the pad is kept in contact with the wall.

Abstract: The present invention relates to the acquisition of seismic signals at different levels in a borehole, in response to the generation of seismic waves by a source placed on the surface or in the vicinity of the surface. The acquisition is carried out by means of a sonde suspended in the borehole from a cable and equipped with an anchoring pad. At each acquisition level, the pad is anchored in the borehole wall to couple the sonde to the formation, and then the pad is released from the wall once the acquisition is over. The signals acquired are then sent to the surface by means of the cable. The force with which the pad is anchored in the wall is controlled by means of a feedback arrangement which includes a sensor arranged in the pad itself. During the sonde movements from one level to another, the pad is kept in contact with the wall.

Abstract: A borehole logging system employs a compressional wave transmitter and a shear wave transmitter. The transmitters are alternately fired to impart compressional and shear waves into the formations surrounding the borehole. A bender-type receiver, spaced apart from the transmitter in the borehole is alternately gated so that the voltages across its pair of piezoelectric planar surfaces are subtracted during the expected time period of symmetrical motion of the receiver to provide a compressional wave output and added during the expected arrival time period of unsymmetrical motion of the receiver to provide a shear wave output.

Abstract: A logging sonde has directivity control of multiple sources and receivers in linear arrays. Each of the sources produces acoustic pulses which are delayed by a time delay between the sources to direct acoustic energy at an angle such that the resulting acoustic wave strikes a vertical formation orthogonally. The reflections of the acoustic pulses are detected with a linear array of receivers. The acoustic pulse detected by each receiver is delayed by an amount such that the total differential moveout for a reflected directional wave is zero.

Abstract: A method and apparatus for obtaining seismic records representing shear waves detected preferentially in a given direction of propagation. The apparatus comprises a velocity transducer deployed to measure the instantaneous particle velocity perpendicular to the direction of propagation of the wave and a rotational transducer measuring the instantaneous rate of particle rotation.

Abstract: A method of producing a seismic signal indicative of the substrata beneath a body of water comprising the steps of: supplying acoustic energy to the body of water; sensing at a predetermined depth the pressure wave reflected from the substrata beneath the body of water and the secondary pressure wave caused by a secondary reflection of the pressure wave from the air-water interface and generating a first signal indicative thereof; sensing at the predetermined depth the particle velocity of the water accompanying the pressure wave reflected from the substrata and the secondary pressure wave and generating a second signal indicative thereof; filtering the second signal such that portions of the second signal that have a frequency that is less than a first frequency are attenuated by the filtering to generate a third signal, the first frequency being less than a second frequency which is equal to the wave propagation velocity of the body of water divided by two times the predetermined depth; and combining the fi

Abstract: A method for boring a hole so that its axis is substantially parallel to the axis of a previously bored hole for positioning an acoustical transmitter and receiver against the hole of the hole being bored so that their position on the wall lies on a horizontal plane through the axis of the bore hole being bored. Then transmitting an acoustical frequency acoustical signal into the wall of the hole. The reflected signal is then received from the adjacent wall along with other unwanted additional reflections. The phase shift is then determined between the transmitted and received signal and the changes in the distance between the wall of the bore hole is then determined.

Abstract: An apparatus is described for acoustically investigating a casing in a borehole with a source of acoustic energy that is directed at the reflecting surface of an acoustic reflector in front of which is an acoustically transparent window. The inclination of the window relative to the reflecting surface is selected to deflect secondary transmissions and thus reduce window produced interferences. Several embodiments are described.

Abstract: An acoustic well-logging transmitting transducer employing a transmitter portion comprising stacked piezoceramic rings and a resonating metallic plate, the dimension of which determines the frequency, and a conical acoustic reflector for causing reflections to impinge omnidirectionally on the wall of the borehole at an angle to enhance shear wave component propagation. A receiving portion of similar construction can also be employed.

Abstract: A method and apparatus for obtaining improved measurements of shear waves in low-velocity lossy formations surrounding a borehole. The method comprises forming an interface between the borehole wall and a solid homogeneous material having a lower velocity than the formation. The geometry and velocity of the homogeneous material provide enhancement of the shear waves at the interface and thereby minimize the effect of interference from undesired compressional waves. Further improvement is obtained by using shear waves whose particles move perpendicular to the travel of the wave, parallel to the plane of the waves and perpendicular to the surface of the material. These are commonly referred to as SV shear waves.

Abstract: Illustrative embodiments of the present invention include a transducer for acoustic well logging, comprising a cylindrical hollow body which is capable of vibrating radially and longitudinally with respect to its axis, and an hemispherical cap coupled to one end of the hollow body. A transducer of this type has a directivity pattern in the range of angles of about 15.degree. to 75.degree. to its axis. This range includes substantially all the acoustic waves whose angles of incidence at the interface between the drilling mud and the formations fall in the range of limit refraction angles typically encountered for the drilling mud commonly used and the various different kinds of formations usually investigated.

Abstract: Electroacoustical transmitting or receiving transducer comprising a flat disc piezoelectric transducer element aligned with a conical reflector. The disc transducer element is positioned to transmit acoustic energy in a direction parallel with a borehole axis and this energy is reflected by the conical reflector so that it impinges upon a borehole wall near the critical angle to provide maximum propagation of energy in the rock in one direction parallel to the borehole. The same transducer arrangement also functions as an efficient directional receiver of acoustic energy.