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: Methods and apparatus are described for the seismic exploration of strata adjacent to a borehole, wherein an arrangement of geophones is lowered into the borehole and clamped to the wall. The geophones are clamped at essentially equal angular distances along the circumference of the borehole. A plurality of such arrangements can be positioned along the longitudinal axis of the borehole. By combining the outputs of the geophones noise signals generated by symmetric guided waves are attenuated. The arrangement can be used for cross-well seismic acquisition and in combination with seismic sources and/or attenuator so as to form an single-unit exploration tool for borehole seismics.

Abstract: A transducer configuration for use in acoustically imaging a target region behind an acoustically reflective layer includes a sonde having a geometrical center and constructed and arranged to support a plurality of transducers. The system includes a first transducer disposed within the sonde at a first distance from the geometrical center for generating a first acoustic pulse and for receiving a first acoustic signal. The acoustic signal comprises a first reflection from the reflective surface, a first set of fluid multiples arising from reflections between the reflective layer and a surface of the first transducer, and a first signal associated with the target area. The system also includes a second transducer disposed within the sonde at a second distance from the geometrical center for generating a second acoustic pulse and for receiving a second acoustic signal.

Abstract: A method and device are disclosed for determining the impedance of the cement bond between a borehole casing and its wellbore. The invention uses a predicted resonance response as a baseline for determining from the observed resonance response the approximate impedance of the cement. Corrections are made to account for various defects in the casing by normalizing the received resonance response.

Abstract: A transducer configuration of an acoustic sensing tool for determining the consistency of a first medium disposed between a layer having a greater acoustic reflectivity than the first medium and a second medium, the sensing tool including a rotating head, wherein the tool comprises first, second and third transducer pairs in a spaced apart configuration, each pair comprising a transmitting transducer for transmitting an acoustic radiation signal in an insonified zone, and receiving transducer having a receiving radiation pattern in a insonified zone, wherein the space between the transmitting and receiving transducers in each pair is constructed and arranged to allow the transmitting and receiving insonified zones to intersect behind but not in the acoustically reflective layer to null reverberation energy therefrom.

Abstract: A method and apparatus for determining the hydraulic isolation of layers in an earth formation. The characteristics of various interfaces between the materials in the borehole are evaluated. An acoustic investigation is performed by directing an acoustic signal at a radial segment of the borehole. The signal passes through the casing and the fill material and produces a resulting signal which has travelled along a path encountering various interfaces in the borehole. This signal is processed to make hydraulic isolation determinations.

Abstract: A transducer configuration disposed within a wellbore sonde for acoustically imaging a target region behind an acoustically reflective layer includes a transmitting transducer for producing a transmitted acoustic beamspread pattern defined by a insonified zone having a width approximately equal to a width of the transmitting transducer and a transmitting main lobe beyond the transmitting collimated zone. The transducer configuration also includes a receiving transducer disposed adjacent the transmitting transducer. The receiving transducer includes an acoustic signal reception pattern defined by a insonified zone having a width approximately equal to a width of the receiving transducer and a receiving main lobe beyond the receiving insonified zone. A beamspread angle defines an amplitude contour forming an outer periphery of the transmitting and receiving main lobes.

Abstract: A method for identifying the boundaries between sequences of rocks laid down in different depositional regimes. The approach used is to search, in well logs or seismic data, for a statistic characteristic of such regimes, and for breaks in that statistic. The preferred statistic used in the method of the present invention is the first moment of the power spectrum of the wavenumber of a suitable physical property as a function of depth. This statistic is calculated rapidly and with excellent depth resolution from the complex-valued autocorrelation function at its zero and unit lag values, respectively, and displayed as a single variable in black-and-white or color. The method of the present invention further includes manipulations that achieve the approximate conversion of the scale (and corresponding display) from its initial dependence on depth to one that is displayed as a function of geologic time.

Abstract: A method is described for providing improved seismic data to a driller to indicate position and spatial extent of a drilling target which may be up to several hundreds of feet ahead of a drill bit. In one embodiment, the method includes the steps of: survey design and data modeling, and definition of a drilling target point and a drilling interruption point; drilling down to a depth at which drilling will be interrupted; interruption of drilling; look-ahead borehole seismic survey (VSP); continuation of drilling; data processing and interpretation; coordinate update for optimum target intersection; and steering of drilling by borehole seismic data interpretation.

Abstract: A system for acoustically imaging a target region behind an acoustically reflective layer includes a transducer configuration for acquiring acoustic image data from the reflective layer and target region, wherein the reflective layer and target region are divided into voxels circumferentially disposed about a central point. The system includes a mechanism for processing the data comprising a transmitting transducer for transmitting a first acoustic pulse, a receiving transducer for detecting a first arrival of a first acoustic reflection signal associated with the first acoustic pulse, and a mechanism for suppressing multiple reflected signals from the acoustic reflection signal associated with the first acoustic pulse, wherein the suppressing mechanism facilitates the acquisition of image data from the target region.

Abstract: A seismic source and seismic detector are placed within a wellbore, and are secured in generally fixed relation within the wellbore. Multiple sources can be utilized, or multiple detectors may be utilized, within a single wellbore. Also, additional sources or detectors may be placed in adjacent wells. The source may be periodically actuated to obtain seismic data, and subsequent actuation may be directly compared with prior actuations to evaluate reservoir characteristics.

Abstract: An acoustic logging tool having an acoustic transmitter and at least one acoustic receiver longitudinally spaced from the transmitter is lowered into a borehole fluid within a tubular member having a known resonant frequency. A pulse of acoustic energy is then transmitted into the tubular member, and acoustic energy traversing the tubular member and formation is detected at the acoustic receiver. A frequency domain transformation is performed on the detected acoustic energy and a cement bond evaluation is performed by comparing transformed detected acoustic energy amplitudes within a predetermined range of the resonant frequency of the tubular member, effectively filtering out acoustic energy which traverses the formation surrounding the tubular member.

Abstract: Transducer arrangement for use as receivers in acoustic borehole measurements, in particular for the purpose of geological steering, stratigraphic imaging and control during drilling of deviated and horizontal wells, whereby transducer sensitivity is focused generally in radial directions normal to the drill string axis in close proximity to the drill bit (45). Two separate and substantially similar transducer elements are adapted to be located at substantially the same axial position along the drill string axis. The transducer elements having their output terminals interconnected with opposite polarities, so as to have a combined minimum response to incident acoustic waves and vibrations being identical at both transducer elements.

Abstract: An apparatus and method for using swept frequency energy to inspect a casing or other body is disclosed. A transducer (75) transmits a swept frequency pulse at a casing and receives the reflection resulting from the pulse's impact against the casing. The reflected energy is translated to a reflection signal and analyzed by a signal processor having an envelope detector (240) which translates the reflection signal into an envelope signal. A microprocessor (260) located within the signal processor analyzes the envelope signal to compute data such as the thickness of the casing and the quality of the cement bond holding the casing.

Abstract: A method of analyzing a spatial series of waveforms, each waveform of which contains components arising from at least two substantially uncorrelated features, includes the steps of sorting the waveforms into groups or bins according to values of one or more of the features, determining a mean waveform for each group or bin, subtracting the mean waveform from each waveform in the group or bin, returning the waveforms to the original order of the series and determining a remaining feature. Binning, the process of sorting waveforms into groups based on values of features, can be performed for one feature determined from the waveform or for several features. All that is required is that the binning criteria are substantially uncorrelated with the feature of interest. An example of a binning criterion can be frequency or period of a component of the waveform. Also a value of a physical parameter calculated from the waveform can be used as a binning criterion.

Abstract: An apparatus for logging a borehole comprises a non-rotating component and a rotating component that is flexibly attached to the non-rotating component and includes a logging head. The rotating component is centralized independently from the non-rotating component such that the rotating component remains centralized as it rotates, regardless of whether the non-rotating component is centralized. The logging head includes at least one signaling device, a hydrostatic pressure balancing system, a sealed, variable-volume fluid reservoir in fluid communication with said transducer, and a motor housed in said logging head for rotating the rotating component. The apparatus can further include a second non-rotating component suspended below the rotating component.

Abstract: A multi-part logging tool that allows measurement of several distinct independent parameters, which are in turn used to solve for secondary parameters that give information about the properties of the cement outside the casing. Secondary parameters affecting the measured signals are: casing thickness, bond of cement to casing, cement acoustic impedance, cement thickness, channel size and channel material. The present invention comprises a rotating tool that supports a plurality of specifically configured transducers that interrogate a region behind casing having a 10 degree azimuthal resolution and a depth of investigation of at least 0.75 inches behind casing. The transducers on the rotating tool include an array of angled beam transducers, a single-housing pitch-catch transducer and a radial, pulse echo transducer.

Abstract: An apparatus and method of visually examining the sidewalls of a bore hole include a down hole video tool lowered into the bore hole by means of a cable and winch on the surface. The apparatus includes a wide angle end video camera positioned at the tip of a lower section and a rotatable side scan video camera mounted inboard from the end video camera. The end video provides a panorama view of a portion of the bore hole, and the side scan video camera provides a detailed close-up 360 degree view of a portion of the bore hole. An upper section houses a power supply/triplexer, a telemetry board, an FM modulator video amplifier transmission board, gyroscope data interface board, and a gyroscope for showing the directional orientation of either camera and apparatus in the bore hole. The gyroscope orientation and the visual image of the portion of the sidewall viewed is transmitted to a video display monitor in an equipment van on the surface.

Abstract: A method for logging a subterranean formation from within a well that has been cased and cemented is disclosed. An acoustic signal is transmitted into the formation from a pulse-echo transducer placed within the wellbore and the first casing echo and the first formation echo are detected. The amplitude and the arrival times of these two echoes, combined with some known information about the wellbore, the casing, and the cement enable several parameters to be calculated. These parameters in turn may be used to image the formation around the well.

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

Abstract: A method of logging an underground formation from within a borehole includes the steps of emitting an electromagnetic signal from a first location in a borehole, determining a time at which the signal is emitted, detecting a direct component of the signal which has passed from the first location to a second location without being reflected, determining a time at which the direct component arrives at the second location and determining the speed of the signal in the underground formation from the time at which the signal is emitted, the time of arrival of the direct component and the spacing of the first and second locations. The speed of the signal can be used for radar logging of the formation.

Abstract: The signal-to-noise ratio of televiewer signals from a rotary sidewall acoustic-beam scanner is improved by replacing the volume of borehole drill fluid that lies in the path of the acoustic beam with a solid medium characterized by a lower coefficient of attenuation than that of the drill fluid.

Abstract: Methods for providing an image at the surface of a formation surrounding a borehole in real-time include associating resistivity measurements with a predetermined number of preselected toolface positions. The resistivity measurements are subjected to data compression and transmitted uphole by MWD telemetry. At the surface, the compressed resistivity measurements are associated with the preselected toolface positions and with a calculated translational distance value. The resistivity measurements are decompressed and/or converted to pixel information. The pixel information is arranged according to toolface position and translational distance to create a high resolution of the formation. These processes are repeated over time so that the image created represents the formation over a selected distance.

Abstract: The invention is a method of determining the thickness of a casing in a wellbore penetrating an earth formation using group delay determined casing resonance extracted from processed reflection signals from an acoustic pulse-echo imaging tool. A first Fourier transform coefficient series is calculated from the digitized reflection signal. Individual samples of the reflection signal are multiplied by their sample index values to obtain a modified digitized data string. A second Fourier transform coefficient series is calculated from the modified digitized data. The complex group delay function is calculated directly from the first and second Fourier coefficient series.

Abstract: A measuring technique for producing a three-dimensional image and information relating to the type of sand, clay or gravel which defines a wall or walls of a deep concealed underground excavation which is filled with a stabilizing liquid, and which technique facilitates accurate and safe construction, utilizes a transducer which irradiates a surface of the excavation with ultrasonic waves and detects the waves which are reflected back thereto. The transducer scans horizontally in incremental stages which occur with a predetermined angle pitch. After each scan is completed, the transducer is vertically displaced by a predetermined amount and the horizontal scan is repeated. The time required for a wave to reach and be reflected back to the transducer is used to determine the distance of the wall from the device.

Abstract: An MWD measuring apparatus and technique using a single transducer mounted on an MWD drill collar near a tubular member, such as an upset or stabilizer blade. The minimum stand-off is the radial difference between the MWD drill collar and the tubular member when the drillstring is side-walled against the borehole wall. Control apparatus connected to the transducer determines elapsed time for each pulse transmitted towards and reflected from the borehole wall. A plurality of round-trip transit time (RTT) values are measured and the results statistically analyzed to identify and verify the RTT.sub.min value corresponding to the minimum stand-off distance. The RTT values may be analyzed directly or using histogram techniques. Once determined, the sound speed of the drilling fluid is calculated as twice the radial difference between the MWD collar and stabilizer blade or upset divided by the RTT.sub.min value.

Abstract: A system for the inspection of a well borehole and the formation around the borehole. The system includes a sealed tubing at the lower end of which is mounted a fiberoptic telemetry module which receives various sensor modules for transmissions of sensed information to the surface. The modular telemetry link and sensor include fluid passageways through which fluid pumped from the surface down the sealed tubing may pass to create a region of optically clear and/or acoustically homogenous fluid in the borehole in the vicinity of the modular telemetry link and sensor. The passage of fluid through the passageways in the modular equipment may also serve to cool the circuits thereof.

Abstract: Fluid production or injection wells may be used to transmit or receive seismic signals by lowering a signal transmitting device within a tubing string disposed in the well and exerting a pressure fluid force on a free bottom end of the tubing string to cause the tubing string to helically deflect within the well and engage the wellbore wall firmly over a large portion of the tubing string to enhance the quality and intensity of the signal transmitted between the transmitting device and the earth formation penetrated by the well.

Abstract: The orientation of vertical fractures in subsurface rock formations is determined. A cross-dipole logging tool collects four-component shear-wave seismic data through a formation interval of interest in a subsurface formation adjacent a well bore. A gyroscope is typically provided to indicate compass orientation of the logging tool. The collected seismic data are then transformed within a time window containing arrivals of the shear waves to a new coordinate system within which the motion of the shear waves becomes linear. In the new coordinate system, the shear wave data are processed to determine the presence and orientation of fractures in the formation.

Abstract: A sonic well logging tool radially measures circumferential cement conditions longitudinally along a well casing. Sonic signals are transmitted from a plurality of angularly displaced transmitter-transducers, through a borehole fluid, down a longitudinally extending sector of the well casing, and then through the borehole fluid to a plurality of angularly displaced receiver-transducers, which are distally disposed from the transmitter-transducers.

Abstract: A differential analysis method can be used to determine the presence or absence of a fluid in contact with a tubing string within a wellbore. The method uses a signal generator and detects tubing-perturbed signals, searches for an initial interfacial indicator within a window, axially aligns indicators within a data series as the detector traverses the tubing, discerns an adjacent interfacial indicator known to be incrementally changed by the presence of the fluid, and compares the adjacent indicators to the known incremental change. Even if the absolute location or condition of the interface is uncertain, the relative change indicates the presence or absence of fluid. A prior condition indicator can also be used to determine a second window for detecting an adjacent surface signal indicators.

Abstract: Pulse echo apparatus and methods are disclosed for measuring characteristics of a borehole while it is being drilled. A component of a bottomhole assembly, preferably a drilling collar, is provided with one or more ultra-sonic transceivers. A pulse echo sensor of the transceiver is preferably placed in a stabilizer fin of the collar, but may also be placed in the wall of the collar, preferably close to a stabilizing fin. Electronic processing and control circuitry for the pulse-echo sensor is provided in an electronic module placed within such collar. Such pulse echo apparatus, which preferably includes two diametrically opposed transceivers, generates signals from which standoff from a borehole wall may be determined. A method and apparatus are provided for measuring standoff and borehole diameter in the presence of drilling cuttings entrained in the drilling fluid.

Abstract: An ultrasonic stand-off gauge for use in measuring the instantaneous stand-off distance between the drill stem and the borehole wall while drilling. A primary transducer mounted on the drill collar sends and receives ultrasonic pulses between the drill collar and the borehole wall. A second, reference transducer mounted on the pressure barrel within the drill collar measures the sound speed of the drilling fluid. The drilling fluid flows through a conduit within the drill collar, where the reference transducer transmits a pulse through the drilling fluid in the conduit. The pulse from the reference transducer is reflected off an internal reflector mounted on the internal surface of the drill collar. Since the distance between the reference transducer and the reflector is known and constant, the sound speed of the drilling fluid is determined accurately.

Abstract: Pulse echo apparatus and methods are disclosed for measuring characteristics of a borehole while it is being drilled. A component of a bottomhole assembly, preferably a drilling collar, is provided with one or more ultra-sonic transceivers. A pulse echo sensor of the transceiver is preferably placed in a stabilizer fin of the collar, but may also be placed in the wall of the collar, preferably close to a stabilizing fin. Electronic processing and control circuitry for the pulse-echo sensor is provided in an electronic module placed within such collar. Such pulse echo apparatus, which preferably includes two diametrically opposed transceivers, generates signals from which standoff from a borehole wall may be determined. A method and apparatus are provided for measuring standoff and borehole diameter in the presence of drilling cuttings entrained in the drilling fluid.

Abstract: An apparatus for reducing or eliminating the effects of a quadrupole component of an acoustic signal received from a transversely mounted acoustic source in a drill collar of a logging while drilling tool. The apparatus includes a drill collar for supporting a drill bit, a transversely mounted transmitter situated in a first horizontal plane in the drill collar which transmits acoustic energy into an earth formation. The drill collar also houses at least one receiver mounted in a second horizontal plane in the drill collar at an angular displacement from the transmitter such that the effects of a quadrupole component of the acoustic energy detected by the receiver are rendered insignificant.

Abstract: A system for the inspection of a well borehole and the formation around the borehole. The system includes a pair of concentric reeled tubings for injecting a pair of fluids into a wellbore through a wellhead, one of said fluids being an optically transparent or acoustically homogenous fluid which forms a slug of said fluid around an optical sensor which transmits signals indicative of well conditions to the surface. The other of said fluids is used to perform functions with respect to said sensor such as cooling said sensor or protect it from a corrosive environment. In addition, a fiberoptic cable construction in combination with the reel tubing is also disclosed.

Abstract: A method and apparatus for spatially filtering a signal set to enhance interface echoes representing a borehole configuration. The spatial filtering technique provides information regarding the various interfaces formed between materials in the borehole environment, as well as thicknesses of the various materials present in the borehole. Further, the presence of channels formed during the cementing procedure are detected.

Abstract: Perforations into an earth formation from a wellbore may be analyzed as to location, shape and radial depth by placing an inspection apparatus in the wellbore including an acoustic signal transmitter for transmitting acoustic signals over a broad bandwidth for a limited time, and receiving reflected or resonant acoustic signals excited in nearby perforations. The amplitude of the resonant frequency will reach a maximum when the perforation is at a midpoint between the transmitter and receiver. The resonant frequencies may be plotted as a function of signal power or intensity to determine perforation radial depth, based on the assumption that the perforation approximates an elongated cylindrical tube. Resonant frequency breadths may be compared to determine relative permeability of the formation and resonant frequency values may be compared to determine the shape of the perforation cavity.

Abstract: Method for determining at least one characteristic of a casing cemented in a borehole, such as cement bond and casing thickness, from a reflected acoustic signal S(t) obtained by directing an acoustic pulse at a substantially normal incidence towards a radial sector of the wall of the casing, the pulse stimulating thickness resonance within the walls of the casing. The method according to the invention comprises the steps of: determining a first time window corresponding to a first portion of signal S(t) including the initial reflection from the casing and subsequent acoustic returns due to resonance, determining a second time window corresponding to a second portion of signal S(t) mainly including the initial reflection from the casing, and determining the casing characteristic from information related to resonance contained in the first time window while normalizing the information by information contained within the second time window.

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 focused acoustic transducer for use with a borehole televiewer wherein the transducer is provided with a concaved surface designed to focus the acoustic energy and reduce the energy present in the side lobes of the near field.

Abstract: The growth of a hydraulic fracture increases the period of free oscillations in the well connected to the fracture. Simultaneously, the decay rate of free oscillations decreases. The properties of forced oscillations in a well also change during fracture growth. All of these effects result from the changing impedance of the hydraulic fracture that intersects the well. Hydraulic fracture impedance can be defined in terms of the hydraulic resistance and the hydraulic capacitance of a fracture. Fracture impedance can be determined directly by measuring the ratio of down hole pressure and flow oscillations or indirectly from well head impedance measurements using impedance transfer functions. Well head pressure measurements can also be used to evaluate fracture impedance by comparing them to pressure oscillations computed with hydraulic models that include fractures with different impedances.

Abstract: A method and an apparatus for recording the depth of a well logging apparatus is provided. The method and apparatus include the direct acquisition of broad depth information from the logging system conversion of the broad depth information to an acceptable digital signal and recording that signal on the audio track of a video cassette recorder. A microcontroller is used to convert broad depth information from either the logging system or the video cassette recorder (in the playback mode) to actual depth and depth rate for use by other displays and plotters.

Abstract: A method for determining the height and length of a fracture (3) in a borehole (1) involves generating pressure waves in the fluid in the wellbore using a valve (4) and measuring the response at the well-head by means of a transducer (5). A theoretical model of the wellbore-fracture system is generated and compared with the measured response to determine the height and length of the fracture.

Abstract: Methods for characterizing acoustic transducers and using a characterized acoustic transducer for measuring cement impedance of a cased well are disclosed. The method for characterizing the acoustic transducer generally comprises: arranging the acoustic transducer a predetermined distance from a calibration target of known thickness; transmitting a pulse from the acoustic transducer through a known medium and toward the calibration target and measuring a return signal received therefrom; and fitting, via minimization, a return signal calculation generated by a model of the return signal which has a limited number of parameters, to the received return signal to determine a value for at least one of the parameters and thereby characterize the transducer. The preferred parameters for characterization are the transducer radius and stand-off, such that the transducer may be characterized as having an effective stand-off and an effective radius.

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 by which fractured rock formations are identified and their orientation may be determined includes two orthogonal motion sensors which are used in conjunction with a downhole orbital vibrator. The downhole vibrator includes a device for orienting the sensors. The output of the sensors is displayed as a lissajou figure. The shape of the figure changes when a subsurface fracture is encountered in the borehole. The apparatus and method identifies fractures rock formations and enables the azimuthal orientation of the fractures to be determined.

Abstract: A method and apparatus for laboratory simulation of the dynamic formation of sand arches in production of oil and/or gas from unconsolidated or poorly consolidated wells is disclosed. An ultrasonic transducer is disposed opposite a perforation in a member simulating the casing of a well and the simulated well is operated at conditions approximating those of interest in the field. The acoustic transducer is moved incrementally across the perforation and measurements of the distance between the transducer and the formation are measured. These can then be used to generate a profile of the surface of the formation behind the perforation. Preferably, an ultrasonic transducer which emits a focussed beam of acoustic energy is employed.

Abstract: In the present invention, characteristics of fractures or microcracks in earth formations surrounding a borehole are detected by use of conventional sonic logging devices used in combination with internal variations of wellborne pressure. A sonic logging tool is first used to generate a log of acoustic velocity at a first pressure. Borehole pressure is then changed and a second log is obtained. Significant changes in formation velocity in response to the pressure change indicates the presence of fractures.

Abstract: Pulse echo apparatus and methods are disclosed for measuring characteristics of a borehole while it is being drilled. A component of a bottomhole assembly, preferably a drilling collar, is provided with one or more ultra-sonic transceivers. A pulse echo sensor of the transceiver is preferably placed in a stabilizer fin of the collar, but may also be placed in the wall of the collar, preferably close to a stabilizing fin. Electronic processing and control circuitry for the pulse-echo sensor is provided in an electronic module placed within such collar. Such pulse echo apparatus, which preferably includes two diametrically opposed transceivers, generates signals from which standoff from a borehole wall may be determined. A method and apparatus are provided for measuring standoff and borehole diameter in the presence of drilling cuttings entrained in the drilling fluid. In a preferred embodiment, such signals are assessed by the electronic processing and control circuity to determine if gas has entered borehole.