Abstract: An electromagnetic tomography system for determining properties of geological formation penetrated by at least one borehole lined with a conductive tubular includes a transmitter disposed in a first borehole and adapted to induce a magnetic field, a first receiver disposed in the first borehole and adapted to detect a magnetic field induced in the conductive tubular by the transmitter, and a second receiver adapted to detect a magnetic field induced in the geological formation by the transmitter.

Abstract: The invention relates to techniques for locating and determining the orientation of a fracture in an earth formation. Systems and methods for detecting a fracture in an earth formation using a propagation tool include producing electromagnetic fields using a TMD transmitter in the tool; measuring corresponding voltage signals detected with one or more TMD receivers in the tool; determining harmonics from the measured signal responses by shifting the responses (e.g. by 90 degrees) and performing an addition or subtraction using the shifted response. In some embodiments, the second harmonic is processed to determine the fracture orientation.

Abstract: Well logging apparatus and methods for determining formation resistivity at multiple (>3) depths of investigation. At least one transmitter antenna and at least two receiver antennas are mounted in a logging tool housing, on substantially a common axis. The antennas are untuned coils of wire. Electromagnetic energy is emitted at multiple frequencies from the transmitter into the formation. The receiver antennas, which are spaced apart from each other and from the transmitter, detect reflected electromagnetic energy. Formation resistivity at multiple depths of investigation is determined using only phase differences in the reflected energy at the different frequencies, minimizing false indications of invasion due to mismatch of vertical response with attenuation measurements and also permitting correcting for the effects of varying dielectric constant of the formation.

Abstract: The present invention provides a method and apparatus for performing resistivity measurements for the purpose of geo-steering with 180-degree azimuth resolution. All the measurements represent a complementary set of data acquired in two operational modes. The directional mode providing sensitivity of the received signals to the azimuth characteristics of the formation. The deep mode provides a large depth of investigation for resistivity determination and bed boundary detection. The directional mode can be implemented using one receiving coil placed in between quadruple type transmitter. The deep mode represents either array induction measurements or multiple propagation resisitivity (MPR) measurements that provide high depth of investigation for resistivity determination and bed boundary detection.

Abstract: The present invention is a propagation resistivity system that utilizes one or more transmitter coil antennas, or “transmitters” and at least two receiver coil antennas, or “receivers”. The system uses a wellbore resistivity tool which may be embodied as a MWD tool or as a wireline tool. Two or more transmitters may be spaced equally on either side of two or more spaced-apart receivers. Two or more frequencies are transmitted and received simultaneously. Multiple frequencies may be transmitted from each transmitter or from separate transmitters at the same time. Multiple frequencies are simultaneously received and analyzed by the receiver electronics, thereby reducing the measurement time for multiple frequency measurements. In one embodiment each of two transmitters transmits simultaneously. One transmitter operates on a high frequency. The second transmitter operates at a lower frequency.

Abstract: An apparatus and method for determining resistivity of a formation surrounding a borehole comprises a housing, at least first and second transmitting antennas affixed to the housing for transmitting electromagnetic waves to the formation, and at least first and second receiving antennas for detecting the electromagnetic waves. The first receiving antenna is affixed to the housing at a position longitudinally located above the first and second transmitting antennas, and the second receiving antenna is longitudinally located below the first and second transmitting antennas. The measurements needed to calculate the resistivity of the formation may be determined while drilling the borehole.

Abstract: An electromagnetic wave propagation resistivity borehole logging system comprising multiple groups of electromagnetic transmitter-receiver arrays operating at three frequencies. The borehole logging tool component of the system employs eight transmitters and four receivers. The transmitters and receivers are disposed axially and symmetrically along the major axis of the tool to form four group pairs. Each group pair consists of a transmitter-receiver groups axially and symmetrically on opposing sides of a reference point on the tool. Each, transmitter-receiver group consists of one transmitter assembly and two receiver assemblies. Each transmitter-receiver group is operated at two of three operating frequencies which are 100 kHz, 400 kHz and 2 MHz. The transmitter and receiver assemblies are fabricated to yield azimuthally symmetrical resistivity measurements in a plane essentially perpendicular to the axis of the tool.

Abstract: An apparatus and method is disclosed for induction logging of electrical properties of earth formations that operates at low frequencies while remaining resistant to skin effect and maintaining mutual balancing. The apparatus includes a plurality of transmitter coils that are at a plurality of distances from a measure point located at an end of the apparatus, and a receiver coil array coupled to receive induced voltages resulting from currents induced in the earth formations by one or more transmitters of the plurality of transmitter coils, wherein the common measure point is located within the receiver coil array, and wherein one or more of the plurality of distances from the measure point are determined according to a function of one or more frequencies associated with one or more transmitters of the plurality of transmitters. According to an embodiment, the function includes determining the distance that is inversely proportional to a square root of the frequency associated with the one or transmitter.

Abstract: Apparatus and methods for measuring cross sectional area and flaws in a continuous sucker rod string as the string is conveyed within a borehole. These measured parameters are useful is monitoring the physical integrity of the sucker rod string. A magnet is used to saturate an increment of continuous sucker rod, and a coil is used to measure induced flux. Cross sectional area of the rod increment is computed from the flux measurement. One or more Hall effect transducers are used to measure leakage from the increment as a function of distance along the increment. This measurement is used to detect and quantify the type of flaw within the rod increment being investigated. The process is repeated as the sucker rod string is conveyed into or out of the borehole.

Abstract: A frequency domain electromagnetic geophysical mapping instrument has a transmitter, a transmitter coil connected to the transmitter, the transmitter generating current pulse waveforms formed by half-sinusoidal output waveform segments of a waveform having a frequency equal to a resonant frequency of the transmitter coil, and a receiver, in which the transmitter generates current pulses including pulses comprising a plurality of immediately successive half-sinusoidal waveform segments of common polarity. The pulses immediately succeed each other and are of alternating polarity. The pulse lengths may in this case be equal, or vary in a manner providing a desired output spectrum, for example according to a pseudo-random sequence.

Abstract: A method and apparatus for imaging deep underground objects utilizes the application of a spectral regularization routine that is applied to measured data prior to the application of an inversion routine to measured surface impedances to map subsurface conductivity. Specifically, measurement of magnetic and electric fields is conducted utilizing sensors at a measurement site, a processor is used to generate either resistivity or conductivity data based on the measurements of the sensors, the processor then performs the spectral regularization routine and an inversion routine to generate data that can be utilized to identify underground targets. The spectral regularization routine and inversion routine can either be processed separately (decoupled) or together. The measurements of the magnetic and electric fields are preferably made under the assumption of the presence of a plane wave at the measurement site.

Abstract: Resistivity data acquired at two different epochs using different types of tools are jointly inverted. For example, a multiple propagation resistivity (MPR) tool is run first, preferably at several frequencies and several transmitter-receiver spacings. At a later epoch, an induction tool may be run, preferably on a wireline. The joint inversion process identifies bed boundaries based on inflection points in the propagation resistivity and induction logging raw data. An initial guess for an uninvaded earth model is generated using the selected bed boundaries and the apparent raw resistivity values. An inversion run using shallow measurements of propagation resistivity logging data is performed to estimate a resistivity structure representative of the near borehole zone resistivity (invaded zone). The bed boundary positions of the layers are also updated as part of the inversion process. Synthetic data for both the shallow and deep measurements are generated to delineate the invasion zones.

Abstract: Arrangements, specific apparatus and associated methods for skin depth compensation in underground boring applications are described. Compensation for skin depth error is accomplished by measuring a locating signal transmitted from a boring tool such that measurements of the locating signal include skin depth error introduced as a result of the electrical conductivity characteristic of the earth. Thereafter, the measurements are used in a way which determines a skin depth corrected position of the boring tool. In one aspect, a multi-frequency approach is provided which utilizes measured intensities of the locating field at two or more frequencies to extrapolate a zero frequency value of intensity. The zero frequency value of intensity is then used in position determination.

Abstract: A resistivity tool for use in an LWD system includes an asymmetric transmitter design with multiple transmitters capable of generating EM signals at multiple frequencies. A pair of receivers are positioned at one end of the transmitter array to detect the EM signals after they have traversed the region in the vicinity of the borehole. A calibrating transmitter is positioned between the receivers, which can be used in two different modes of operation. In a first mode, the calibrating transmitter is used to calibrate the receivers for thermal drift. In this calibration mode, an attenuation correction and phase shift correction can be calculated to correct for thermal drift of the receivers while the resistivity tool is in the borehole. Thus, the thermal drift of the receivers can be re-calibrated as often as desired while the tool is in the well. In a second mode of operation, the calibrating receiver may be used to measure the resistivity of the drilling mud in the borehole.

Abstract: A method and apparatus for detecting mostly-plastic mines having steel firing pins and copper igniter cups. A frequency spectrum is transmitted, and response signals from the metal components induced by resultant eddy currents are detected. The firing pin generates a response characterized by a first frequency that is in phase with the transmitted frequency, whereas the igniter cup generates a response characterized by a second frequency that is in quadrature with the transmitted frequency. Accordingly, the detected response can be compared to prestored response templates to determine what type of mine, if any, has been detected, with the use of two response frequencies and phase relationships enabling the discrimination of buried plastic mines from surrounding metal particles in the earth.

Abstract: A method for determining horizontal resistivity of an anisotropic formation and a formation anisotropy response factor with an induction logging tool is claimed. The method utilizes two differing induction type measurements to determine the horizontal resistivity for the formation without knowledge of a borehole dip angle. The differing induction measurements may be different types of measurements or the same type of measurement made under differing operating conditions. The method further discloses a means for determining the vertical resistivity of an anisotropic formation based on the dip angle, the horizontal resistivity and the formation anisotropy response factor.

Abstract: A spectrogram of secondary magnetic field strength as a function of frequency and spatial relationship is used to identify hidden objects. A time-varying multi-frequency primary electromagnetic field is generated, preferably over the range 100 Hz to 300 kHz, which induces a time-varying multi-frequency secondary electromagnetic field about the hidden object. The strength of the secondary field, typically inphase and quadrature, is plotted as a spectrogram over a low frequency broadband spectrum as a function of frequency and spatial relationship between the hidden object and the secondary field strength detector. From this spectrogram, indications may be had of the hidden object's characteristics such as location, size and shape, and material composition. Preferably, the measured spectrogram is compared against a library of reference spectrograms by a computer to identify the hidden object.

Abstract: A balanced bandpass preamplifier assembly (23) is disclosed for use in a locator (10) for locating a beacon transmitter (18) housed within an underground boring device (12). The bandpass preamplifier assembly (23) includes a balanced bandpass filter (28) of the Butterworth type with second order filter characteristics. The preamplifier assembly (23) provides reception of beacon frequencies at two distinct frequencies, preferably 29.430 KHz and 32.768 KHz. The antenna (14) of the . locator (10) forms the series inductance in the bandpass filter (28).

Abstract: An emitter for a system of electromagnetic tomographic measurements, as well as a process and a generator (5) adapted to produce a variable frequency current supplying a solenoid (1), constituted of turns wound about a magnetic core (3). The solenoid (1) is constituted by several windings (4a, 4b, 4c) disposed side by side with each other on the core (3), and the emitter comprises switching means (6) adapted to connect in series or in parallel and/or to disconnect the different windings (4a, 4b, 4c) with and from each other, constituting the solenoid (1), so as to control the number of active turns of the solenoid (1).

Abstract: An apparatus and method for performing geological mapping utilizes an HF transmitter to heat ionospheric electrons to cause the current in an overhead electrojet to be modulated, thereby injected a low frequency EM signal into the Earth-ionosphere waveguide. A sensor measures vector values of electric and magnetic fields in an area to be surveyed. The measured vector values are provided to a processor that creates a conductivity map of the surveyed area based on the measured vector values.

Abstract: aN emitter for a system of electromagnetic tomographic measurement, as well as a process and a generator (5) adapted to produce a variable frequency current supplying a solenoid (1), constituted of turns wound about a magnetic core (3). The solenoid (1) is constituted by several windings (4a, 4b, 4c) disposed side by side with each other on the core (3), and the emitter comprises switching means (6) adapted to connect in series or in parallel and/or to disconnect the different windings (4a, 4b, 4c) with and from each other, constituting the solenoid (1), so as to control the number of active turns of the solenoid (1).

Abstract: A system for detecting metal targets located in a background environment such as the ground evaluates metal targets by processing components of signals at two or more different frequencies. A component of the received signal induced by the ground can be eliminated by subtracting signal components measured at two different frequencies. The received signal can be processed to account for changes in the background response with frequency. The type of an unknown target can be identified by processing background excluded components to produce data characterizing the target type.

Abstract: The device comprises a target signal transmitter to induce an electromagnetic signal in the hidden object, a position reference transmitter to transmit a signal for positioning purposes, a sensor unit to detect changes in the magnetic flux of the hidden object due to the induced electromagnetic signal and the positioning signal from the position reference transmitter, and a central unit to process and display a map of the hidden object. The initial processing of the data results in a gray-scale representation of the object, but additional data processing may be performed.

Abstract: Apparatus and methods for determining an indication of a nonlinear property of a formation traversed by a borehole are provided. An acoustic tool is used in a borehole to generate first and second signals of different frequencies. As a result of nonlinearities in the formation, the mixing of the first and second signals results in a third signal having a frequency equal to the difference of the frequencies of the first and second signals. The amplitude of the third signal is measured by a detector, and the indication of nonlinearity of the formation is determined according to a relationship which relates the measured amplitude at the measured frequency to the amplitudes of the first and second signals, the frequency of measurement, the velocity of the measured wave, the distance of the receiver from the source, and a function of the nonlinear and linear parameters of the formation.

Abstract: In an MWD system, a mandrel for connection to the drill bit is set forth which supports shallow, intermediate and deep measuring resistivity systems. By transmitting upwardly and downwardly in alternate fashion, and receiving the transmitted signal at pairs of receiver coils, transmitted signal phase shift and attenuation are measured. A method of measuring is set forth which includes making resistivity measurements close to the drill bit at increasing ranges from the borehole so that formation resistivity prior to fluid invasion is obtained. Measurements are thus provided of formation resistivity before, during and after fluid invasion. The method also accommodates formations which have a relative dip angle with respect to the well borehole.

Abstract: An embodiment of the present invention is a toxic waste containment facility subject to leaking hazardous plumes into soils beneath and adjacent to the site. The facility includes a plurality of substantially horizontal underground drillholes adjacent to and below a waste containment pit. A radio transmitter and antenna are placed in a first underground drillhole proximate to a surface waste containment site. A radio receiver and antenna are placed in a second underground drillhole opposite to the first drillhole. A position indicator is used for gauging a plurality of locations of the radio transmitter and antenna within the first underground drillhole and the radio receiver and antenna within the second underground drillhole. A data processing unit analyzes data received from radio receiver and antenna and position indicator to measure radio signal attenuation between the radio transmitter and antenna and radio receiver and antenna.

Abstract: A slot antenna has a square aperture and two current probes at angles to each other in the aperture. The two current probes are excited simultaneously or separately with different signals. By adjusting the amplitude or phase of the signals in the current probes, the angle of the magnetic moment of the antenna can be adjusted. An array of such antennas in an electromagnetic propagation tool for a well-logging device simultaneously provides better standoff performance by adjusting tile magnetic moment to be parallel to a borehole axis, and better image response by adjusting the magnetic moment to be perpendicular to the formation bed. The array can be excited to function as an endfire and broadside array of an electromagnetic propagation tool.

Abstract: An apparatus and method for determining formation resistivity at a plurality of radial distances from an earth borehole uses a single receiver pair and a plurality of electromagnetic energy transmitters sequentially spaced along the apparatus from the receiver pair, such transmitters being sequentially pulsed at approximately 1-2 MHz each to provide time separation between the pulsing of the plurality of transmitters. The closest spaced transmitter is spaced a predetermined distance from the closer receiver to make the depth of investigation of the closest transmitter essentially independent of formation resistivity. Alternatively, a single transmitter is spaced a predetermined distance from the closer receiver to make the depth of investigation of such transmitter essentially independent of formation resistivity.

Abstract: The present invention generally relates to a system for use in determining the location and orientation of concealed underground objects and, more particularly, to an improved locator system having a unique and improved interface with an operator. In accordance with one embodiment of the invention, a magnetic field detector for locating concealed underground objects is provided. The magnetic field detector includes a housing having an upper housing portion and a lower housing portion. A receiver is disposed within said housing for receiving magnetic field signals from the concealed underground objects. A swivel joint couples the upper housing portion and the lower housing portion to permit relative rotational motion.

Abstract: A method and apparatus for determining electromagnetically the locations of electrically conductive bodies beneath the surface of the ground, wherein a primary electromagnetic field is generated with the aid of a loop through which a sinusoidal alternating current is passed. The loop is placed at or above the level of the ground beneath which the locations of conductive bodies shall be determined. There are currents generated in the conductive bodies which, in turn, generate a secondary electromagnetic field. The values of the amplitude and phase of the magnetic component of the thus formed total electromagnetic field are measured with the aid of coils mounted inside a probe which is lowered to different depths in a borehole. The values of the primary field phase are measured continuously by at least one reference coil which is placed outside the probe, either above or beneath the surface of the ground, within the propagation area of the primary field.

Abstract: A method utilized with an underground conductor detection system for calibrating a downhole transmitter to compensate for detuning of the transmitter antenna by geologic formations. The method comprises sending a synchronization signal to the transmitter antenna, measuring the current flow through the transmitter antenna and adjusting the current to a constant level, and measuring the phase difference between the transmitter antenna current and the synchronization signal. A receiver transmitter is calibrated by sending a synchronization signal to a radiating antenna in the receiver that in turn sends a calibration signal to the receiver antenna that is directed over the entire signal pathway back to surface located signal processing equipment. Another method of underground conductor detection sends a surface wave to the downhole receiver to cancel the effect of the surface wave modulation on a target wave being radiated by the underground detector.

Abstract: Induction logging apparatus is disclosed which depends for its operation not only upon its arrangement of coils, but also upon the skin depth of the formation. The skin effect of the formation is used advantageously by operating a simple induction sonde at a plurality of frequencies simultaneously. Improved depth of investigation and improved vertical resolution result from the invention. Simple arrays are disclosed for the induction logging apparatus. A sonde with a single transmitter and a plurality of two-coil receiver arrays are preferred. The apparatus acquires both the in-phase and quadrature components of each receiver array signal at several frequencies. The response function is shaped by using a multi-channel deconvolution filter.

Abstract: A method utilized with an underground conductor detection system for calibrating a downhole transmitter to compensate for detuning of the transmitter antenna by geologic formations. The method comprises sending a synchronization signal to the transmtter antenna, measuring the current flow through the transmitter antenna and adjusting the current to a constant level, and measuring the phase difference between the transmitter antenna current and the synchronization signal. A receiver transmitter is calibrated by sending a synchronization signal to a radiating antenna in the receiver that in turn sends a calibration signal to the receiver antenna that is directed over the entire signal pathway back to surface located signal processing equipment. Another method of underground conductor detection sends a surface wave to the downhole receier to cancel the effect of the surface wave modulation on a target wave being radiated by the underground detector.

Abstract: A transmitter for an induction well logging tool, adapted to be disposed in the borehole of an oil well, develops an output signal for energizing the borehole formation which inherently consists of six separate signal components, the six components including four primary signal components which simultaneously energize the borehole formation inducing in the formation four primary eddy currents. These four primary eddy currents are detected by the array induction tool receiver, the received signals being used to determine the resistivity and conductivity of the borehole formation.

Abstract: A conducting metal discriminating detection apparatus which uses at least two different frequencies and in preference 3 to interrogate a target. The detection apparatus distinguishes reactive and resistant components of each of the received signals and combines these in such a way as to avoid effects of background such as ironstone in one case or salt water in another.

Abstract: A method and device for measuring peak gamma radiation is provided wherein the method includes the steps of determining a minimum and maximum number of counts within a preselected multiple channel energy spectrum measurement range, determining a channel having approximately one-half the number of maximum counts, determining a channel representing a background energy, computing a peak energy centroid channel, computing a channel to energy conversion factor and recomputing the boundry channels for the preselected multiple channel energy spectrum measurement range.

Abstract: A method for direct airborne electromagnetic prospecting of hydrocarbons by transmitting many primary electromagnetic fields and detecting any deviation of the primary electromagnetic fields due to secondary electromagnetic fields. The transmitting and detecting operations are carried out first over a known area comprising a known petroleum deposit and known barren locations (a stage of system instruction) and then over an unknown area to be explored (a stage of actual prospecting). The enormous volume of data obtained in both stages is processed electronically, using pattern recognition theory, into a probability level of the hydrocarbon presence or absence for all measuring points over the unknown area. In the stage of system instruction, the detected signal deviations are converted into factors of discriminant functions by substituting the high absolute probability levels for known hydrocarbon deposit and barren locations (above +0.8 and below -0.8, respectively) into these functions.

Abstract: An electrical geophysical method and system for direct and diagnostic prospecting of hydrocarbon deposits. Numerous combinations of connections of the transmitting array and numerous combinations of frequencies are employed in sequence to create many unique electromagnetic fields in the earth, first over a number of locations known to contain hydrocarbons and known to be barren, then over prospecting locations. Numerous electric and magnetic components of each electromagnetic field are measured with a receiving array located in the near field of the transmitting array. The huge amounts of measured data are processed using Pattern Recognition techniques in a processor to yield directly a probability measure of hydrocarbon occurrence at each prospecting location.

Abstract: A method and apparatus for improving signals used for detecting conductive bodies in an area by means of an airborne electromagnetic survey system, comprising the steps of generating and transmitting an AC primary field signal, the frequency spectrum of which comprises a DC component or a low frequency component, and radiating this primary field signal to the said area and receiving induced secondary field signals which are generated by the said conductive bodies and further comprising the step of processing the received secondary field signals and representing the processed signals in order to derive information whether or not conductive bodies in the said area are present.

Abstract: The depth to and size of an underground object may be determined by sweeping a CSAMT signal and locating a peak response when the receiver spans the edge of the object. The depth of the object is one quarter wavelength in the subsurface media of the frequency of the peak.

Abstract: A wireline logging system for measuring formation resistivity includes a longitudinal housing having three transmitters and three receivers arranged at measured distances on the housing, with about four feet between the outermost ends of the array. The transmitters are operated at three different frequencies, with each receiver receiving all three frequencies. The output of each receiver is the three received frequencies, which is amplified and fed to a mixer. A local oscillator frequency is also fed to each mixer. The output from each mixer of the three received frequencies mixed with a local frequency is passed through a filter to output one of the three received signals at a lower frequency. The frequency mix is arranged so that the output of each of the filters is at a common frequency.

Abstract: The secondary signals induced in the receiver coils of two or three transmitter-receiver coil-pairs flown over terrain to be surveyed are combined to provide additional data relating to the terrain. One of the coil-pairs is arranged in a whaletail configuration, and the other or others in standard and/or fishtail configurations. The inphase and/or quadrature secondary whaletail and standard or fishtail signals are combined in such a manner as to cancel responses due to conductive overburden and distributed magnetite, and the whaletail and standard (or fishtail) signals are compared to differentiate anomalies caused by thin and thick steeply dipping conductive layers.

Abstract: In a sub-soil prospecting process a vertical magnetic field transmitter dipole and a receiver dipole are placed on the ground, away from each other. The receiver dipole is oriented to detect a radial horizontal magnetic field relative to the transmitter dipole. At low frequencies, the magnetic field detected assumes asymptotic values, and by measuring these values an apparent alternating current resistivity of the sub-soil is deduced. By varying the transmitter-receiver distance, and by simultaneously using a direct current electric prospecting process, a sub-soil model is determined which is less ambiguous than those supplied by electric or induction prospecting alone.

Abstract: This invention relates to electromagnetic mapping wherein magnetic fields of two or three different and normally audio frequencies may be transmitted or received efficiently using induction coils with the same orientation and essentially the same spatial location. Flat, air cored coils are used and are overlapped so as to have essentially zero mutual inductance between pairs.

Abstract: A direct and continuous receiving and measuring device for electrical, magnetic and acoustic signals comprises an amplifier stage and a broadband filtering stage at the input, a local oscillator for supplying a reference signal, a measuring stage, a mixer to which the local oscillator and the broadband filtering stage are connected and a low frequency filtering stage connected to the mixer.The invention also includes the process of carrying out the measurement.