Abstract: A method for electromagnetic exploration includes imparting a first electromagnetic signal into subsurface formations from a first location and imparting a second electromagnetic signal into the formations from a second location substantially contemporaneously with imparting the first electromagnetic signal. The first and second electromagnetic signals are substantially uncorrelated with each other. A combined electromagnetic response of the formations to the first and second imparted electromagnetic signals is detected at a third location. A response of the formations to each of the first and the second imparted signals is determined from the detected response.

Abstract: A system and method include receiving electromagnetic energy emanating from a target using a plurality of receivers, and generating a pseudo-source based at least in part on a location of one or more of the plurality of receivers and the received electromagnetic information.

Abstract: At least one antenna array including three mutually orthogonal antennas each sharing a common center point senses an electromagnetic signal emitted by a buried object such as a utility line, pipe or sonde. A circuit at least partially mounted in a housing is connected to the array and determines a location of the buried object by measuring signal strength and field angles in three dimensions without having to align the antenna array relative to the buried object while eliminating nulls and false peaks. A graphical user interface (GUI) has user-friendly icons, symbols, menus, numbers and graphical and auditory representation of signal strength. A plurality of different underground objects can be simultaneously detected and their different locations can be simultaneously indicated to a user via audible sounds and/or visual images on a display.

Abstract: A method for noise signal analysis and communication with an underground transmitter. The method comprises the steps of measuring a noise floor when no signal is transmitted from a transmitter, detecting a signal when the transmitter is transmitting, and estimating the noise free component of the signal by removing the noise floor measurement. The measurement of the noise floor and detecting the signal from the transmitter may be done using a root mean square technique. The noise floor measurement can be removed from the measured signal by subtracting the noise floor measurement from the measured signal or alternatively by calculating the square root of the difference between the square of the measured signal and the square of the noise floor measurement. The noise estimation technique may be used in connection with, a differential phased shift keying communication scheme or other modulation techniques.

Abstract: A method for analysing acquired electromagnetic measurements (R) made at or in a sea (4) over a seafloor (1) with rock formations (3) having relatively low resistivity (?3) for detecting a possibly underlying petroleum bearing reservoir formation (2) having relatively high resistivity (?2), wherein a low frequency electromagnetic transmitter (5) arranged in the sea (4) emits an electromagnetic field (P) propagating in the sea (4), in the rocks (3, 2) and in the air (0) above the sea; wherein electromagnetic sensors (6) are arranged with desired offsets (x) in the sea (4) for measuring the electromagnetic field (P(x)) while the field propagates, characterized in that one or more component of the electromagnetic field (P) is measured at least one large offset (xL) from the transmitter (5) where the field (P) essentially only has its origin from the field propagating as a field (P0) through the air (0); that the one or more components of the electromagnetic field (P) measured at the large offset (xL) is calculat

Abstract: A resistivity array having a modular design includes a transmitter module with at least one antenna, wherein the transmitter module has connectors on both ends adapted to connect with other downhole tools; and a receiver module with at least one antenna, wherein the transmitter module has connectors on both ends adapted to connect with other downhole tools; and wherein the transmitter module and the receiver module are spaced apart on a drill string and separated by at least one downhole tool. Each transmitter and receiver module may comprise at least one antenna coil with a magnetic moment orientation not limited to the tool longitudinal direction. A spacing between the transmitter and receiver module may be selected based on expected reservoir thickness.

Abstract: The present invention improves measurement of the formation induction response in the presence of the primary magnetic field generated by a logging tool's transmitter. A structure is provided having a new combination of electrical and mechanical design features which provide logging tool for internal calibration and checking of antenna performance and characteristics before during and after well logging operations.

Abstract: A method for determining a component of electric field response of the Earth's subsurface to a time-varying electromagnetic field induced in the Earth's subsurface is provided. The method includes measuring electric field response along a nonlinear pattern on at least one of the Earth's surface and the bottom of a body of water. The method includes measuring magnetic field response in three directions along the nonlinear pattern on at least one of the Earth's surface and the bottom of the body of water. The method further includes determining an electric field response in a direction normal to the measured electric field response using the electric field response and magnetic field response measurements.

Abstract: A device for guiding energy in a subsurface electromagnetic measuring system is provided, the device including a transmitting member for transmitting an electromagnetic signal into a subsurface medium, an energy-guiding member disposed in magnetic communication with the electromagnetic signal, and a receiving member for receiving a return signal induced from the subsurface medium. A method of guiding energy in a subsurface measuring system is also provided, the method including transmitting an electromagnetic signal into a subsurface medium, modifying the electromagnetic signal using a magnetic field, and then receiving a modified return signal induced from the medium using a receiving member.

Abstract: A method is proposed for a marine electromagnetic survey based on the TM mode, for the purpose of prospecting for and detecting subsurface hydrocarbon reservoirs. The method includes an electromagnetic field source (1113) that, in a submerged, essentially vertical transmitter antenna, generates and injects electric current pulses (81,82) with a sharply defined termination. An electromagnetic field generated by these pulses (81,82) is measured by at least one receiver (1109) provided with an essentially vertical receiver antenna (1111) submerged in water, during the interval when the current in the transmitter antenna (1108) of the electromagnetic field source (1113) is switched off. The distance between the electromagnetic field source (1113) and the at least one receiver (1109) is smaller than the depth of the target object. An apparatus is also described, for implementation of the method.

Abstract: A method for mapping sub-surface resistivity contrasts comprising making multi-channel transient electromagnetic (MTEM) measurements using at least one electric source with grounded input current electrodes or one magnetic source with current in a wire loop or multi loop and at least one electric field or magnetic field receiver, measuring the resultant earth response simultaneously at each receiver using a known recording system, measuring the system response by measuring directly the current in the wire at the source using effectively the same recording system, using the measured system response to recover the impulse response of the earth from each measured earth response, and creating from such impulse responses a sub-surface representation of resistivity contrasts.

Abstract: A system for determining resistivity of a region below a geologic surface by transmitting a signal from a marine location above the sea floor to a receiver comprises a vertical dipole, vertical coil, or other antenna. The receiver may have a vertical dipole, including a first conductor structure and a second conductor structure, as well as a first member. The first conductor structure may be disposed below the sea floor and the second conductor structure may be disposed above the first conductor structure. The receiver may receive the signal at the sea floor. The system may be used in a method that includes releasing the remote reader from a surface vessel, activating a drive head on the remote reader, creating a hole in the sea floor, and disposing a first conductor structure within the hole.

Abstract: A device rotates at least one static magnetic field about an axis, producing a rotating magnetic dipole field, and is movable in relation to the surface of the ground. The field is periodically sensed using a receiver to produce a receiver output responsive to the field. A positional relationship between the receiver and the device is monitored using the output. In one aspect, changing the positional relationship, by moving the device nearer to a boring tool which supports the receiver, causes an increase in accuracy of depth determination. In another aspect, determination of an actual overhead position of the boring tool, and its application, are described. Use of a plurality of measurements over at least one-half revolution of each magnet is disclosed. Establishing a surface radial direction toward a boring tool and resolution of multi-valued parameters is described. Calibration techniques, as well as a three transmitter configuration are also described.

Abstract: A system for investigating subterranean strata. An electromagnetic field and a seismic event are applied from the same location and the responses are detected using respective receivers both located at a second location spaced from the first. The responses are combined to identify the presence and/or nature of subterranean reservoir. The refracted wave components are used.

Abstract: Measurements made with an induction logging tool are processed to provide a resistivity model of fluid invasion of the formation. Up to five zones can be determined over a radial distance of about 0.6 m. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Abstract: Apparatus and method for estimating the 3D orientation angles for remotely deployed devices with flexible arms such as dipole antennas of receivers used in marine controlled-source electromagnetic surveys to explore for hydrocarbons. Acoustic transponders or transducers, or other positioning sensors such as attitude sensors or strain-sensitive fiber optic cables are placed on each electrode arm of the receiver. Acoustic sensors (101) on the receiver frame (94) work in conjunction with the positioning sensor(s) (101) on the electrode arms (92) to provide accurate 3D spatial position of the receiver electrodes (93) relative to the receiver frame. Alternatively, sonar transducers mounted on the frame are used to image the electrode arms, which image can be enhanced by fixing reflectors to the arms. An attitude sensor is mounted on the receiver frame, enabling conversion of the relative electrode positions to an earth reference frame.

Abstract: Characterizing a reservoir with electromagnetic imaging surveys includes normalizing measured voltage data by transmitter moment, sorting the normalized voltage data into common receiver profiles, densely resampling transmitter locations using common positions for the receiver profiles, coarsely resampling the data at discreet transmitter locations, defining a starting model for inversion, weighting the data by a factor, converting the normalized voltage data to ratios, calculating a conductivity image using a ratio inversion method, and verifying that an inversion has converged and the image is geologically reasonable. The image can then be displayed. The invention can be used for cross-well, surface-to-borehole, and borehole-to-surface measurements by which the effects of steel casing are reduced.

Abstract: A receiver system (18) for an electromagnetic prospecting system is disclosed. The electromagnetic prospecting system comprises a transmitter for transmitting a primary electromagnetic field so as to generate a secondary electromagnetic field from a terrain that is being prospected, the secondary electromagnetic field having a transient, decaying time domain profile. The receiver system (18) comprises first and second sensors (20, 22) for detecting the secondary electromagnetic field, wherein the second sensor (22) is less sensitive than the first sensor (20) so as to detect the secondary electromagnetic field over a first time period, with the first sensor (20) being used to detect the secondary electromagnetic field after the first time period. Typically, each sensor (20, 22) comprises three orthogonal SQUID magnetometers, with the second sensor (22) being approximately 10 times less sensitive than the first sensor (20).

Abstract: A method of analyzing results from an underwater controlled source electromagnetic (CSEM) survey of an area that is thought or known to contain a subterranean hydrocarbon reservoir is described. The method is based on a wavefield extrapolation of narrow-band electromagnetic field data obtained from pairs of source and receiver locations. The data comprise a plurality of discrete frequencies between 0.01 Hz and 60 Hz. The wavefield extrapolation is performed for each of these discrete frequencies to provide distributions of electromagnetic scattering coefficient as a function of position and depth beneath the survey area. These distributions may then be combined to provide a displayable image of electromagnetic scattering coefficient. The method is able to quickly provide a displayable image that is readily interpretable.

Abstract: A method for tracking a sinusoidal electromagnetic signal in noisy data using a Kalman filter or other tracking algorithm. The method is useful for controlled source electromagnetic surveying where longer source-receiver offsets can cause the source signal to decay significantly and be difficult to retrieve from magnetotelluric or other electromagnetic background.

Abstract: Two embodiments of marine geo-electric probe methods for hydrocarbon deposits survey comprise—excitation of electromagnetic field in a surveyed medium by transmitting two rectangular current pulses therethrough, the first—during forward traveling of a probe device along a profile and the second—during backward traveling thereof, —measuring instant values of the first and second electric potential differences during the time between the pulses, wherein, the equal-zero condition of the electric potential differences along the profile is ensured, —calculating three sets of normalized electrical parameters based on difference values, —solving an inverse problem via a differential equation for the dipole source voltage in an electrochemically polarizable medium using the parameters, —producing data according to said electrical parameters, and—determining conductivity of the medium, induced-polarization factor and decay time constant of the polarization potential difference.

Abstract: A method for electrical survey of hydrocarbons deposits under seabed depths up to 1500 m and equipment therefor are provided. The equipment includes a vessel, a generator, an excitation field block, connected with a vertical dipole with coax electrodes, a data registration/processing block, bottom systems with. The lower dipole electrode is situated at maximally 100 m from the seabed, the upper electrode at maximally 200 m from the surface. The operation of the generator and bottom systems is synchronized the dipole is submersed into the sea, and fed with alternating-sign rectangular current pulses, whose on-off time ratio and duration are programmably determined. The bottom systems register reflected signals and electromagnetic field components, when the dipole's current is on and off.

Abstract: A method is disclosed for determining earth vertical electrical anisotropy from offshore electromagnetic survey measurements. The method requires both online and offline data, which includes at least one electromagnetic field component sensitive at least predominantly to vertical resistivity and another component sensitive at least predominantly to horizontal resistivity. Using a horizontal electric dipole source, online EZ and offline HZ measurements are preferred. For a horizontal magnetic dipole source, online HZ and offline EZ data are preferred. Magnetotelluric data may be substituted for controlled source data sensitive to horizontal resistivity. Maxwell's equations are solved by forward modeling or by inversion, using resistivity models of the subsurface that are either isotropic or anisotropic.

Abstract: A sea electrical survey method for carbohydrates deposits, situated under seabed not exceeding 10 meters of depth, is disclosed, comprising: providing a plurality of multi-channel bottom systems with receiving lines having at least three electrodes and capable to register electromagnetic signals, excitation means generating a series of alternating-sign pulses controlled by a computer a horizontally positioned dipole, synchronizing the excitation means and bottom systems, submerging the systems upon the seabed along a predetermined direction, aligning the receiving lines, moving the dipole within the survey zone, excitation of the pulses, registering signals measuring the potentials difference and the spatial derivatives of the signals during the pulses and the pauses, recording data, analyzing the data with accounting the fields behavior in time and in space simultaneously, determining the environment resistivity and environment polarizability based on a predetermined mathematical model, and compiling the dep

Abstract: An electromagnetic logging that includes a support; and at least one four-coil array disposed on the support, wherein the at least one four-coil array comprises: a transmitter, a bucking coil, a receiver, and a trim coil. A method for balancing an induction array includes applying an alternating current to a transmitter of the induction array that comprises the transmitter, a bucking coil and a receiver; measuring a mutual coupling between the transmitter and the receiver; and adding an extra bucking coil, if the mutual coupling exceeds a selected criterion.

Abstract: A method for determining formation electrical properties includes deploying one or more receivers for electromagnetic logging; obtaining measurement data indicative of the formation electrical properties using the deployed receivers; correcting the measurement data for receiver imperfection; and inverting the corrected measurement data to obtain one or more parameters of formation electrical properties.

Abstract: An electromagnetic receiver includes at least one sensor for measuring electromagnetic signals, and a calibration antenna configured to generate an electromagnetic signal at a first frequency.

Abstract: A detector for underwater electromagnetic surveying is described. The detector comprises first, second, third and fourth electrodes which are arranged to define first, second and third electric dipole antennae extending between pairs of the electrodes. Each dipole antennae extends between a pair of the electrodes and the fourth electrode is common to all three dipole antennae. Thus the first electrode is separated from the fourth electrode along a first direction to provide the first dipole antenna, the second electrode is separated from the fourth electrode along a second direction to provide the second dipole antenna, and the third electrode is separated from the fourth electrode along a third direction to provide the third dipole antenna. The electrodes are arranged so that the first, second and third directions are inclined at an angle of between 20 and 70 degrees to a surface on which the detector rests when in normal use.

Abstract: A method for monitoring a high-resistivity reservoir rock formation (2) below one or more less resistive formations (3). The method includes transmitting an electromagnetic signal (S) propagating from near a seafloor or land surface (1) by means of an electromagnetic transmitter (5) powered by a voltage signal generator (G). The electromagnetic signal (S) propagates from the seafloor (1) and is guided along a conductive string (7) to the high-resistive formation (2), and propagates as a guided-wave electromagnetic signal (S2) at a relatively higher speed (V2) inside the high-resistivity formation (2) than a propagation speed (V3) in the less resistive formations (3).

Abstract: The present invention, in various embodiments, is directed to a geophysical system and method in which a transmitter coil is oriented with its axis horizontally, and a sensor is positioned below the coil to measure an ambient electrical and/or magnetic parameter associated with a conductive medium surrounding the at least one transmitter coil.

Abstract: A logging radar system and method for measuring propped fractures and down-hole formation conditions in a subterranean formation including: a radar source; an optical source; an optical modulator for modulating an optical signal from the optical source according to a signal from the radar source; a photodiode for converting the modulated optical signal output from the optical modulator to the source radar signal; a transmitter and receiver unit; and a mixer. The transmitter and receiver unit receives the source radar signal from the photodiode, transmits the source radar signal into the formation and receives a reflected radar signal. The mixer mixes the reflected radar signal with the source radar signal to provide an output. This technology can be used to describe all fractures connected to the wellbore and differentiate between the dimensions of the two vertical wings of a propped fracture.

Abstract: Location determination is performed using a transmitter including an elongated generally planar loop antenna defining an elongation axis. The elongation axis is positioned along at least a portion of a path. A magnetic field is then generated which approximates a dipole field. Certain characteristics of the magnetic field are then determined at a receiving position radially displaced from the antenna elongation axis. Using the determined certain characteristics, at least one orientation parameter is established which characterizes a positional relationship between the receiving position and the antenna on the path. The magnetic field may be transmitted as a monotone single phase signal. The orientation parameter may be a radial offset and/or an angular orientation between the receiving position and the antenna on the path. The antenna of the transmitter may be inserted into a first borehole to transmit the magnetic field to a receiver inserted into a second borehole.

Abstract: A device rotates at least one static magnetic field about an axis, producing a rotating magnetic dipole field, and is movable in relation to the surface of the ground. The field is periodically sensed using a receiver to produce a receiver output responsive to the field. A positional relationship between the receiver and the device is monitored using the output. In one aspect, changing the positional relationship, by moving the device nearer to a boring tool which supports the receiver, causes an increase in accuracy of depth determination. In another aspect, determination of an actual overhead position of the boring tool, and its application, are described. Use of a plurality of measurements over at least one-half revolution of each magnet is disclosed. Establishing a surface radial direction toward a boring tool and resolution of multi-valued parameters is described. Calibration techniques, as well as a three transmitter configuration are also described.

Abstract: A method processing an electromagnetic wavefield response in a seabed logging operation. The wavefield is resolved into upgoing- and downgoing components. The downgoing component represents reflections from the sea surface while the upgoing component represents reflections and refractions from subterranean strata. The upgoing component is then subjected to analysis.

Abstract: A tool for performing electromagnetic measurements within a borehole includes a transmitter including a coil having N-turns wound coaxially around a long metallic mandrel and a receiver including a coil having a one-turn receiving loop wound coaxially around the mandrel; wherein the transmitter is adapted for providing a current I of a predetermined frequency f of a maximum intensity in a predetermined part of a near borehole zone; and wherein the receiver is disposed a distance L from the transmitter and adapted for receiving a signal from the transmitter. A method for use of the tool is provided.

Abstract: A method of processing an electromagnetic wavefield response in a seabed logging operation. The wavefield is resolved into upgoing and downgoing components. The downgoing component represents reflections from the sea surface while the upgoing component represents reflections and refractions from subterranean strata. The upgoing component is then subjected to analysis.

Abstract: A geophysical prospecting method and apparatus that utilizes the harmonics and sub harmonics waves induced into the earth by the electric power grid. The amplitude-frequency data are converted to amplitude-depth data and further converted to a differential curve. The resulting differential curve is compared to known patterns of the interested geological features, such as hydrocarbon reservoir, to identify whether the features exist and at what depth such geological features lie.

Abstract: An underground prospecting method and apparatus that utilizes the harmonics and fractional harmonic waves induced into the earth by the electric power grid. The data are converted to amplitude-depth and phase-depth data. The resulting data may be plotted and are compared to known patterns of the interested underground features, such as hydrocarbon, water, minerals and cavities, to identify whether the features exist and at what depth such underground features lie.

Abstract: A signaling apparatus comprises a magnet and a shield moveable relative to the magnet. The shield is moveable relative to the magnet between a first position in which the magnet is relatively exposed and a second position in which the magnet is relatively shielded. The apparatus can include a synchronization signal source, a downhole sensor signal source, and/or means for modulating the magnetic field in response to the signal from any source. A method of using the signaling apparatus to locate a bottomhole assembly includes moving the shield so as to modulate the magnetic field created by the magnet, sensing the modulation of the magnetic field, and determining the location of the bottomhole assembly using the information collected. The BHA can be located using phase shift or amplitude measurements. Receivers detecting the modulated magnetic field can be at or below the earth's surface.

Abstract: Location determination is performed using a transmitter including an elongated generally planar loop antenna defining an elongation axis. The elongation axis is positioned along at least a portion of a path. A magnetic field is then generated which approximates a dipole field. Certain characteristics of the magnetic field are then determined at a receiving position radially displaced from the antenna elongation axis. Using the determined certain characteristics, at least one orientation parameter is established which characterizes a positional relationship between the receiving position and the antenna on the path. The magnetic field may be transmitted as a monotone single phase signal. The orientation parameter may be a radial offset and/or an angular orientation between the receiving position and the antenna on the path. The antenna of the transmitter may be inserted into a first borehole to transmit the magnetic field to a receiver inserted into a second borehole.

Abstract: A system for detecting or determining the nature of a subterranean reservoir. An electromagnetic field is applied using a dipole antenna transmitter and this is detected using a dipole antenna receiver. The measurements are taken with the antenna both in-line and parallel and the difference between the two sets of measurements is exploited. A characteristic difference indicates a high resistive layer, which corresponds to a hydrocarbon reservoir.

Abstract: A transverse induction logging tool having a transmitter and receiver for downhole sampling of formation properties, the tool having a symmetrical shielded split-coil transmitter coil and a bucking coil interposed between the split transmitter coils to reduce coupling of the transmitter time varying magnetic field into the receiver. The tool provides symmetrical shielding of the coils and grounding at either the transmitter or receiver end only to reduce coupling of induced currents into the received signal. The tool provides an insulator between receiver electronics and the conductive receiver housing having contact with conductive wellbore fluid, to reduce parasitic current flowing in a loop formed by the upper housing, feed through pipe, lower housing and wellbore fluid adjacent the probe housing or mandrel. An internal verification loop is provided to track changes in transmitter current in the real and quadrature component of the received data signal.

Abstract: The present invention relates to a system and apparatus for detecting and recovering hydrocarbons located in a subterranean reservoir In some embodiments, an electromagnetic field is applied by a transmitter positioned on a seabed and detected by antenna also positioned on the seabed.

Abstract: A resistivity logging tool suitable for downhole use includes a transmitter, two spaced apart receivers. The measured resistivities at the two receivers are corrected for differences in receiver characteristics based on measuring the responses of the receivers to a calibration signal passed through calibration circuits. The logging tool may be used in reservoir navigation. A calibration antenna positioned between the two receivers may be used to identify factors other than the distance to a bed boundary that may effect the receiver signals.

Abstract: An electromagnetic survey method for surveying an area previously identified as potentially containing a subsea hydrocarbon reservoir, comprising obtaining first and second survey data sets with an electromagnetic source aligned end-on and broadside relative to the same or different receivers. The invention also relates to planning a survey using this method, and to analysis of survey data taken in combination allow the galvanic contribution to the signals collected at the receiver to be contrasted with the inductive effects, and the effects of signal attenuation, which are highly dependent on local properties of the rock formation, overlying water and air at the survey area. This is very important to the success of using electromagnetic surveying for identifying hydrocarbon reserves and distinguishing them from other classes of structure.

Abstract: There is disclosed a method of selecting, in real time, a soil stabilizing protocol for clay-bearing soils occurring in construction sites. The method includes the steps of: obtaining soil conductivity data values at locations within a defined site without disturbing the surface of the soil; correlating the soil conductivity data values with corresponding estimates of soluble sulfate levels; recommending a calcium-based soil stabilizing protocol if the estimated level of soluble sulfates is less than a predetermined threshold; and performing a laboratory analysis of soil samples from selected portions of the defined site when the estimated soluble sulfate concentration equals or exceeds the predetermined threshold.

Abstract: A system for detecting or determining the nature of a subterranean reservoir. An electromagnetic field is applied using a dipole antenna transmitter and this is detected using a dipole antenna receiver. The measurements are taken with the antenna both in-line and parallel and the difference between the two sets of measurements is exploited. A characteristic difference indicates a high resistive layer, which corresponds to a hydrocarbon reservoir.

Abstract: An induction logging tool is used on a MWD bottom hole assembly. Due to the finite, nonzero, conductivity of the mandrel, conventional multi frequency focusing (MFF) does not work. A correction is made to the induction logging data to give measurements simulating a perfectly conducting mandrel. MFF can then be applied to the corrected data to give formation resistivities.

Abstract: Systems and methods utilizing an elongated sub body adapted to receive a run-in tool within its inner bore. The run-in tool including nuclear sources and sensors to provide nuclear formation evaluation while tripping. The nuclear sources and sensors align with partially or fully penetrating windows in the sub to allow for measurements through the sub. The sub wall includes an inner passage adapted to direct radiation energy emitted from within the sub back to the sub bore to align the run-in tool within the sub. The sub also includes fully penetrating openings in its walls to provide through-tubular signal passage. Hydraulic isolation at the sub openings is provided by pressure barrier means. A run-in tool configuration also includes antennas, neutron, and gamma-ray sources/sensors to provide a retrievable triple combo system.

Abstract: Location determination is performed using a transmitter including an elongated generally planar loop antenna defining an elongation axis. The elongation axis is positioned along at least a portion of a path. A magnetic field is then generated which approximates a dipole field. Certain characteristics of the magnetic field are then determined at a receiving position radially displaced from the antenna elongation axis. Using the determined certain characteristics, at least one orientation parameter is established which characterizes a positional relationship between the receiving position and the antenna on the path. The magnetic field may be transmitted as a monotone single phase signal. The orientation parameter may be a radial offset and/or an angular orientation between the receiving position and the antenna on the path. The antenna of the transmitter may be inserted into a first borehole to transmit the magnetic field to a receiver inserted into a second borehole.