Abstract: Systems and methods for monitoring a characteristic of a subterranean hydrocarbon reservoir and for placing a borehole in the vicinity of a well in an earth formation. New well completion systems with slotted stations are utilized to provide through-casing signal-transmission and/or reception. Hydraulic isolation between the interior and the exterior of the completion is provided by pressure barrier means at the slotted stations. The completions permit temporary or permanent monitoring of changes in reservoir saturation with the use of mobile sources/sensors. The completions also form part of a system for accurately placing a well within a desired distance and orientation relative to an existing well.

Abstract: A shielding method and apparatus for an antenna disposed on an elongated support adapted for disposal within a borehole. The shield providing predetermined attenuation of one or more electromagnetic energy field components as the field components interact with the shield. The shield composed of a flexible strip or cylindrical body and respectively comprising a transverse conductive element or a transverse slot therein. The shields being adapted to cover an antenna mounted on the support. The shields being compatible for use in conjunction with saddle, tilted coils or multi-layered tri-axial coils to produce a pure transverse magnetic dipole electromagnetic field. The shields are also used in methods for shielding an antenna disposed on a support to provide predetermined attenuation of an electromagnetic field component as the field components interact with the shield.

Abstract: Methods and apparatus are disclosed for minimizing or eliminating an undesired axial electric current induced along a subsurface borehole in the process of subsurface measurements with transmitter and/or receiver antennas which are substantially time varying magnetic dipoles with their dipole moments aligned at an angle to the axis of the borehole. Some antennas are disposed within the borehole on instruments having a non-conductive support member. One instrument includes a conductive all-metal body with an antenna adapted for induction frequencies. Antenna shields adapted for controlled current flow are also provided with an all-metal instrument. Methods include providing an alternate path for the current along the instrument body. Another method includes emitting a controlled current to counter the undesired current. Another method corrects for the effect of the current using a superposition technique.

Abstract: There is disclosed herein a method of enhancing the vertical resolution of an induction tool, in a manner that may advantageously also reduce undesirable borehole and “negative resistivity” effects. In one embodiment, the method comprises: a) obtaining a vertical magnetic dipole (VMD) response signal from a transmitter-receiver array of antenna elements having magnetic dipoles oriented parallel to a tool axis; b) obtaining a horizontal magnetic dipole (HMD) response signal from a transmitter-receiver array of elements having magnetic dipoles oriented perpendicular to the tool axis; and c) combining the VMD and HMD response signals to obtain a combination response signal. When the relative weights of the VMD and HMD response signals are set as described herein, the combination response signal (and any log calculated therefrom) has a narrow, substantially rectilinear, vertical measurement profile. Further, the combination response signal is relatively insensitive to borehole effects.

Abstract: Methods and apparatus are disclosed for minimizing or eliminating an undesired axial electric current induced along a subsurface borehole in the process of subsurface measurements with transmitter and/or receiver antennas which are substantially time varying magnetic dipoles with their dipole moments aligned at an angle to the axis of the borehole. Some antennas are disposed within the borehole on instruments having a non-conductive support member. One instrument includes a conductive all-metal body with an antenna adapted for induction frequencies. Antenna shields adapted for controlled current flow are also provided with an all-metal instrument. Methods include providing an alternate path for the current along the instrument body. Another method includes emitting a controlled current to counter the undesired current. Another method corrects for the effect of the current using a superposition technique.

Abstract: Methods and apparatus are disclosed for minimizing or eliminating an undesired axial electric current induced along a subsurface borehole in the process of subsurface measurements with transmitter and/or receiver antennas which are substantially time varying magnetic dipoles with their dipole moments aligned at an angle to the axis of the borehole. Some antennas are disposed within the borehole on instruments having a non-conductive support member. One instrument includes a conductive all-metal body with an antenna adapted for induction frequencies. Antenna shields adapted for controlled current flow are also provided with an all-metal instrument. Methods include providing an alternate path for the current along the instrument body. Another method includes emitting a controlled current to counter the undesired current. Another method corrects for the effect of the current using a superposition technique.

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: A coil array for high resolution induction logging comprises a transmitter, a first receiver set and a second receiver set. The second receiver set includes at least one portion of the first receiver set. A method for deriving an apparent conductivity log from at least one induction well log that comprises a plurality of depth samples, comprises raising each depth sample to several predetermined powers, convolving in depth the powers of conductivity, and summing the convolutions to produce a conductivity log. An apparatus for measuring the resistivity of an earth formation, comprises a transmitter energized by a time-varying, periodic voltage, a set of receivers generating a receiver voltage, an analog-to-digital converter that outputs a digitized voltage signal, and a processor that receives the digitized voltage signal.

Abstract: A coal bed anomaly detection and imaging system comprises a synchronous transmitter and receiver that are separated by a geologic structure with embedded and hidden anomalies. The transmitter sends out two signals from magnetic dipole antennas. Such signals are widely separated in frequency but synchronized internally in the transmitter to one another. The higher frequency is used to make phase shift and attenuation measurements at the receiver by synchronous detection. The lower frequency is used at the receiver to synchronize the receiver to the transmitter. The higher frequency signal is measurably affected by anomalies in the intervening geologic structure. The lower frequency signal is fixed low enough so it is not substantially affected by the intervening geologic structure. Geologic modeling tools are preferably downloaded by geoscientists to their personal computers.

Abstract: A coal bed anomaly detection and imaging system comprises a synchronous transmitter and receiver that are separated by a geologic structure with embedded and hidden anomalies. The transmitter sends out two signals from magnetic dipole antennas. Such signals are widely separated in frequency but synchronized internally in the transmitter to one another. The higher frequency is used to make phase shift and attenuation measurements at the receiver by synchronous detection. The lower frequency is used at the receiver to synchronize the receiver to the transmitter. The higher frequency signal is measurably affected by anomalies in the intervening geologic structure. The lower frequency signal is fixed low enough so it is not substantially affected by the intervening geologic structure. Geologic modeling tools are preferably downloaded by geoscientists to their personal computers. The total attenuation and phase shift measurements are plugged into a full-wave inversion code (FWIC) process.

Abstract: Techniques are provided to transform attenuation and phase measurements taken in conjunction with a drilling operation into independent electrical parameters such as electrical resistivity and dielectric values. The electrical parameters are correlated with background values such that resulting estimates of the electrical parameters are independent of each other. It is shown an attenuation measurement is sensitive to the resistivity in essentially the same volume of an earth formation as the corresponding phase measurement is sensitive to the dielectric constant. Further, the attenuation measurement is shown to be sensitive to the dielectric constant in essentially the same volume that the corresponding phase measurement is sensitive to the resistivity. Techniques are employed to define systems of simultaneous equations that produce more accurate measurements of the resistivity and/or the dielectric constant within the earth formation than are available from currently practiced techniques.

Abstract: Systems and methods are provided for determining various subsurface formation parameters from electromagnetic measurements. Formulas are disclosed for field components in a coordinate system tied to the logging tool. Closed form expressions for a magnetic field distribution in a homogeneous anisotropic medium are derived from Moran-Gianzero formulas. A complete coupling of a tri-axial system of transmitters and receivers is derived in the tool coordinate system, allowing direct inversion of the measurements for horizontal and vertical conductivity and dip and strike (dip-azimuth) angles. Closed form expressions for these four quantities in the low frequency limit are also derived.

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. Some of the transmitter and receiver assemblies are fabricated to yield azimuthally focused resistivity measurements, and to yield vertical and horizontal resistivity in anisotropic dipping beds.

Abstract: Methods and apparatus are disclosed for minimizing or eliminating an undesired axial electric current induced along a subsurface borehole in the process of subsurface measurements with transmitter and/or receiver antennas which are substantially time varying magnetic dipoles with their dipole moments aligned at an angle to the axis of the borehole. Some antennas are disposed within the borehole on instruments having a non-conductive support member. One instrument includes a conductive all-metal body with an antenna adapted for induction frequencies. Antenna shields adapted for controlled current flow are also provided with an all-metal instrument. Methods include providing an alternate path for the current along the instrument body. Another method includes emitting a controlled current to counter the undesired current. Another method corrects for the effect of the current using a superposition technique.

Abstract: A shielding method and apparatus for an antenna disposed on an elongated support adapted for disposal within a borehole. The shield providing predetermined attenuation of one or more electromagnetic energy field components as the field components interact with the shield. The shield composed of a flexible strip or cylindrical body and respectively comprising a transverse conductive element or a transverse slot therein. The shields being adapted to cover an antenna mounted on the support. The shields being compatible for use in conjunction with saddle, tilted coils or multi-layered tri-axial coils to produce a pure transverse magnetic dipole electromagnetic field. The shields are also used in methods for shielding an antenna disposed on a support to provide predetermined attenuation of an electromagnetic field component as the field components interact with the shield.

Abstract: Systems and methods are provided for directional propagation-type logging measurements not sensitive to dip and anisotropy over a wide frequency range. Estimates of the distance of the logging tool to a bed boundary are obtained using “up-down” measurements with antenna configurations having tilted magnetic dipoles. These estimates are insensitive to anistropy and dip, undesirable complications of directional measurements.

Abstract: A shield apparatus for use in conjunction with a well tool to selectively attenuate one or more electromagnetic energy field components as the components interact with the shield. The shield composed of a flexible strip or conductive body and comprising at least one sloped slot or sloped conductive element therein. The shield being adapted to surround an antenna mounted on a well tool. A method for rotating the axis of the magnetic dipole of a transmitter or receiver coil. A method for winding and shielding an electric coil such that the resultant coil emits or receives selected electromagnetic energy field components.

Abstract: An integrated, single collar measurement while-while-drilling tool is presented that comprises formation sensors, directional sensors, pressure sensors, a mud pulse telemetry device, and a turbine-generator power device configured in a single collar housing that is no longer than a standard drill collar. No electrical connections are made across drill collar tool joints. The tool provides high reliability and ease of transportation.

Abstract: A device for detecting changes of resistivity or dielectrical properties due to changes of fluid composition in the near-well area about a well in a geological formation, comprising an electrically conductive tubing string, an electrical energy source, a signal generator, at least one transmitting antenna for emitting electromagnetic waves along the tubing string, one or more receiver antennas for receiving electromagnetic waves reflected along the tubing string, devices for receiving signals induced in the receiver antennas, signal processing means for processing the received signals, and communication devices for transmitting signals representing the electrical signals and for receiving control signals.

Abstract: Systems and methods are provided for determining subsurface formation properties using an antenna system disposed within a borehole traversing the formation. A logging system includes a well tool implemented with an antenna system having transverse or tilted magnetic dipoles. One antenna implementation uses a set of three coils having non-parallel axes. Through mechanical or electromagnetic rotation of an antenna about its axis in order to maximize or minimize couplings, the systems and methods are used to estimate formation anisotropic resistivity, providing reduced borehole effects in vertical and small deviation wells. This invention may also be applied in deviated wells when the borehole is perpendicular to the strike direction, as is often the case in wireline logging.

Abstract: Systems and methods are provided for determining subsurface formation properties using an antenna system disposed within a borehole traversing the formation. A logging system includes a well tool implemented with an antenna system having transverse or tilted magnetic dipoles. One antenna implementation uses a set of three coils having non-parallel axes. Through mechanical or electromagnetic rotation of an antenna about its axis in order to maximize or minimize couplings, the systems and methods are used to estimate formation anisotropic resistivity, providing reduced borehole effects in vertical and small deviation wells. This invention may also be applied in deviated wells when the borehole is perpendicular to the strike direction, as is often the case in wireline logging.

Abstract: Methods and apparatus are disclosed for canceling or eliminating borehole eccentricity effects on a formation resistivity measurement obtained with transmitter and/or receiver antennas which are substantially time varying magnetic dipoles with their dipole moments aligned at an angle to the axis of the borehole. Various apparatus are configured with a plurality of antennas having tilted or transverse magnetic dipole moments, at least one current sensor, means for conducting alternating current through one or more of the antennas, and means for calculating a scaling factor from signal measurements and for scaling the alternating current with the factor. One method includes scaling an alternating current and passing said current through one or more antennas to obtain the resistivity measurement.

Abstract: In one embodiment the invention comprises a system for generating an image of an Earth formation surrounding a borehole penetrating the formation. Resistivity of the formation is measured using a DC measurement, and conductivity and resistivity of the formations is measured with a time domain signal or AC measurement. Acoustic velocity of the formation is also measured. The DC resistivity measurement, the conductivity measurement made with a time domain electromagnetic signal, the resistivity measurement made with a time domain electromagnetic signal and the acoustic velocity measurements are combined to generate the image of the Earth formation.

Abstract: A multi-mode resistivity tool for use in a logging-while-drilling (LWD) system includes an asymmetric transmitter design with multiple transmitters capable of generating electromagnetic (EM) signals at multiple depths of investigation. An array of at least three receivers is positioned amongst a transmitter array to detect the EM signals after they have traversed the region in the vicinity of the borehole. In a first mode, two pairs of receivers combine with the asymmetrical transmitter array to produce a plurality of compensated resistivity measurements. In an alternative mode, one pair of receivers, consisting of a receiver from each of the previous pairs, combines with the array of transmitters to create a plurality of non-compensated measurements. This multi-mode capability enables the resistivity tool to operate successfully in a wide variety of drilling formations and under a broad scope of drilling conditions.

Abstract: A probe serving for detecting the structure of a dielectric medium. The probe includes at least one transmitter/receiver antenna located near a dielectric boundary surface that defines a dielectric medium, and a signal processor for receiving signals from the antenna and generating data representative of the structure of the dielectric medium. Between the antenna and the face is inserted a cushion of a material having a dielectric number higher than that of the air. In one embodiment, the probe is adapted to inspect if there is a void in the soil around a dielectric pipe, for example a sewer pipe. In this case, the probe is guided inside the pipe with the antennas located on a shaft mounted on the probe with the same axis as the axis of the pipe. Due to the presence of the cushion, an optimally good connection between the antennas and the face defining the dielectric medium is obtained.

Abstract: An electromagnetic antenna extension assembly for connection downhole into a pipe string between a data transmission unit and an electromagnetic antenna. Further, a method for connecting the data transmission unit with the antenna utilizing the assembly. The antenna includes an outer antenna member and an inner antenna member having a lower electrical connector. The data transmission unit includes an outer transmission member and an inner data transmission tool having an upper electrical connector connectable with the lower connector of the inner antenna member.

Abstract: In one embodiment the invention comprises a system for generating an image of an Earth formation surrounding a borehole penetrating the formation. Resistivity of the formation is measured using a DC measurement, and conductivity and resistivity of the formations is measured with a time domain signal or AC measurement. Acoustic velocity of the formation is also measured. The DC resistivity measurement, the conductivity measurement made with a time domain electromagnetic signal, the resistivity measurement made with a time domain electromagnetic signal and the acoustic velocity measurements are combined to generate the image of the Earth formation.

Abstract: A method for detecting electrical properties in a geological formation in a well which has within it a tubing string comprising the steps of mounting a transmitter antenna outside of the tubing string in a fixed position with respect to the geological formation, mounting a receiving antenna outside of the tubing string in a fixed position with respect to the geological formation, generating a first series of electromagnetic waves at a first time, receiving a first series of reflected electromagnetic waves in the receiver antenna, transforming the first series of reflected electromagnetic waves to form a first registration, generating a second series of electromagnetic waves at a second time, receiving a second series of reflected electromagnetic waves in the receiver antenna, transforming the second series of reflected electromagnetic waves to form a second registration, and comparing the registrations. Also disclosed is a device for accomplishing the method.

Abstract: Shoulder corrections are applied to measurements obtained from a multi-component electromagnetic logging tool. An anisotropic resistivity model is obtained using the shoulder corrected data. The process is iterated until a good match is obtained between the shoulder corrected data and the model output.

Abstract: A logging tool is disclosed having transmitting and receiving antennas to measure formation anisotropy. The antennas may preferably be combinations of toroidal, horizontal electric dipole, and horizontal magnetic dipole antennas. In one embodiment, the tool: (a) induces a current flow in the tubing or drill string traversing the formation in a borehole; (b) measures a signal difference between two receiver antennas on the drill string; (c) determines an apparent conductivity of the formation from the resistive component of the signal difference; and (d) uses the apparent conductivity to calculate an anisotropy coefficient with a knowledge of the horizontal conductivity. The tool may further determine a second apparent conductivity of the formation from the reactive component of the signal difference, and use both apparent conductivities to calculate the anisotropy coefficient and the horizontal conductivity. The vertical conductivity can also be determined from these two calculated values in the usual manner.

Abstract: Methods and apparatus for making subsurface measurements with reduced or eliminated borehole effects. Antenna and electrode configurations address the undesired axial electric currents that are induced along the borehole when antennas with tilted or transverse axes are used to make electromagnetic measurements. Current and measure electrodes are used in combination with antennas to limit the flow of undesired axial borehole currents. Embodiments use passive, active, or semi-active electrodes to limit the undesired current flow.

Abstract: A coal mining operation begins by using directional drilling to bore several horizontal shafts through a coal deposit with its natural overburden still intact. Any methane gas permeating the coal deposit is pumped out and preferably sold as natural gas to commercial and residential customers, or used locally in support of mining operations. The methane gas evacuation continues until the concentrations are reduced to safe levels for mining. But before mining begins, ground penetrating radar equipment is lowered into the boreholes for electronic imaging studies of the coal deposit. One borehole is used for a transmitter and another for a receiver. Many measurements are made at a variety of frequencies and equipment positions within the boreholes. Such studies estimate the electrical conductivity of the surrounding material, and thereby give clues where and how much coal is actually deposited.

Abstract: A method is provided for detecting geophysical anomalies. Electrical energy is capacitively accumulated with a charging circuit until a breakdown voltage of a switch is reached. Thereafter, the accumulated electrical energy is discharged by passing a discharge current through a transmitter antenna to transmit an electromagnetic pulse into a geophysical region. This technique allows an increase in the strength of an electromagnetic sounding signal, while simultaneously reducing energy consumption, and thereby also permitting smaller weights and dimensions for the power supply.

Abstract: A sonde is movable lengthwise in and relative to tubular structure such as a drill collar; slits extend through the tubular structure; and antennae coils on the sonde come into registration with the slits, for transmitting electromagnetic energy into the underground formation via certain slits, and for receiving such transmitted energy back through other of the slits, for processing.

Abstract: The invention is a device for measuring and surveillance of resistivity in a petroleum reservoir in a geological formation with an injection-, observation- or production well comprising an electrically conductive metallic well tubing, with the new and inventive being characterized by the following features: a) an electrical energy source; b) at least one inductive transmitter antenna for electromagnetic waves, fixedly arranged in the well, outside of the well tubing's outer metallic surface; c) at least one series of sensors comprising n inductive resistivity sensors (5a, 5b, . . . , 5n) arranged for receiving the electromagnetic waves and generation of measurement signals, fixedly arranged in the well, by the petroleum reservoir and outside the well tubing's outer metallic surface; and d) a signal conductor for the measurement signals.

Abstract: This invention is directed to a downhole method and apparatus for simultaneously determining the horizontal resistivity, vertical resistivity, and relative dip angle for anisotropic earth formations. The present invention accomplishes this objective by using an antenna configuration in which a transmitter antenna and a receiver antenna are oriented in non-parallel planes such that the vertical resistivity and the relative dip angle are decoupled. Preferably, either the transmitter or the receiver is mounted in a conventional orientation in a first plane that is normal to the tool axis, and the other antenna is mounted in a second plane that is not parallel to the first plane. This invention also relates to a method and apparatus for steering a downhole tool during a drilling operation in order to maintain the borehole within a desired earth formation.

Abstract: A method and system for determining the location of a microseismic event is disclosed. An electromagnetic sensor measures the electromagnetic energy which is caused by a microseismic event. Seismic data from the microseismic event is measured and recorded using plurality of ground motion sensors. The time at which microseismic event occurred is estimated based at least in part on the time at which electromagnetic energy caused by the microseismic event is received by the electromagnetic sensor. The location of said source of the microseismic event is determined using the estimated occurrence time and the time at which the seismic energy arrived at the ground motion sensors. A method of triggering a seismic recording device is also disclosed. The electromagnetic energy from a microseismic event is measured and recorded using an electromagnetic sensor. The time at which the microseismic event occurred is estimated based on the measured electromagnetic energy.

Abstract: A coating composite is provided for a platform surface of an antenna array for, when applied to the platform, affording isolation of radiating and receiving antennas of the array. The coating composite includes a plurality of conductively coated elongate tubes dispersed in an insulating polymer matrix at a volume loading density approaching that at which the composite begins to conduct electrically over macroscopic distances, i.e., close to the percolation threshold. The tubes are preferably comprised of microtubules comprised of biologically-derived, high-aspect rod-shaped particles of microscopic dimensions having an electroless plated metal coating thereon.

Abstract: An apparatus and method for determining a location and an orientation of an underground boring tool by employment of a radar-like probe and detection technique. The boring tool is provided with a device which generates a specific signature signal in response to a probe signal transmitted from above the ground. Cooperation between the probe signal transmitter at ground level and the signature signal generating device provided at the underground boring tool results in accurate detection of the boring tool location and, if desired, orientation, despite the presence of a large background signal. Precision detection of the boring tool location and orientation enables the operator to accurately locate the boring tool during operation and, if provided with a directional capacity, avoid buried obstacles such as utilities and other hazards. The signature signal produced by the boring tool may be generated either passively or actively, and may be a microwave or an acoustic signal.

Abstract: Methods and apparatus are disclosed for minimizing or eliminating an undesired axial electric current induced along a subsurface borehole in the process of subsurface measurements with transmitter and/or receiver antennas which are substantially time varying magnetic dipoles with their dipole moments aligned at an angle to the axis of the borehole. Some antennas are disposed within the borehole on instruments having a non-conductive support member. One instrument includes a conductive all-metal body with an antenna adapted for induction frequencies. Antenna shields adapted for controlled current flow are also provided with an all-metal instrument. Methods include providing an alternate path for the current along the instrument body. Another method includes emitting a controlled current to counter the undesired current. Another method corrects for the effect of the current using a superposition technique.

Abstract: The invention subject of this specification utilizes the technique of inductive magnetic coupling of Electromagnetic waves to EM barrier materials in combination with transmission of Electromagnetic waves through non-permeable material to facilitate the measurement of resistivity of geologic formation beyond the well casing.

Abstract: A multi-mode resistivity tool for use in an LWD system includes an asymmetric transmitter design with multiple transmitters capable of generating EM signals at multiple depths of investigation. An array of at least three receivers is positioned amongst a transmitter array to detect the EM signals after they have traversed the region in the vicinity of the borehole. In a first mode, two pairs of receivers combine with the asymmetrical transmitter array to produce a plurality of compensated resistivity measurements. In an alternative mode, one pair of receivers, consisting of a receiver from each of the previous pairs, combines with the array of transmitters to create a plurality of non-compensated measurements. This multi-mode capability enables the resistivity tool to operate successfully in a wide variety of drilling formations and under a broad scope of drilling conditions.

Abstract: An apparatus and a method for controlling oilfield production to improve efficiency includes a remote sensing unit that is placed within a subsurface formation, an antenna structure for communicating with the remote sensing unit, a casing joint having nonconductive “windows” for allowing a internally located antenna to communicate with the remote sensing unit, and a system for obtaining subsurface formation data and for producing the formation data to a central location for subsequent analysis. The remote sensing unit is placed sufficiently far from the wellbore to reduce or eliminate effects that the wellbore might have on formation data samples taken by the remote sensing unit. The remote sensing unit is an active device with the capability of responding to control commands by determining certain subsurface formation characteristics such as pressure or temperature, and transmitting corresponding data values to a wellbore tool.

Abstract: A method is disclosed for determining a diameter of a wellbore. The method includes inducing an electromagnetic field in the wellbore and a formation surrounding the wellbore from a first location along the wellbore. At a first time, a phase is measured, with respect to the field at the first location, of a signal induced by the electromagnetic field at a second and at a third location axially spaced apart from the first location and from each other. The measuring is repeated at a second time, and a resistivity of the formation, and the wellbore diameter at the first time and at the second time are determined from the measurements of phase made at the first and at the second times. Any ambiguity in the resistivity is resolved by using resistivity determined from the measurements made at the first time.

Abstract: Systems and methods for monitoring a subsurface formation property and for placing a borehole in the vicinity of a well in the formation. A slotted tubular is utilized to provide through-tubular signal transmission and/or reception using an antenna adapted to generate a magnetic dipole moment with a transverse or controllable orientation. Hydraulic isolation between the interior and exterior of the tubular at the slot is provided by a pressure barrier. The tubular also forms part of a system for accurately placing a well within a desired distance and orientation relative to an existing well.

Abstract: Borehole orientation information, typically azimuth and inclination, is derived from measurements of gravitational and magnetic components along a borehole axis (O) and transverse thereto. The transverse components are measured by a fluxgate (12) and accelerometer (14) arranged to rotate around the borehole axis (O) at a constant angular velocity (w). The calculations necessary to derive the desired parameters are detailed.

Abstract: A borehole survey method is provided for processing continuous measurements of the earth's magnetic and gravitational fields obtained while drilling a borehole. The present invention improves borehole acquisition of targeted geological structures by substantially reducing continuous measurement errors attributable to noise, shock and vibrations from turning the drill bit against rock.

Abstract: A method and apparatus for determining the size or diameter of boreholes extending to a wide range of dimensions and/or the resistivity of the surrounding earth formations utilizing a well tool disposed in the borehole. The method involves generating model data representative of the well tool responses to different borehole diameters contrasted with formation and borehole fluid resistivity values, determining the borehole fluid resistivity, transmitting electromagnetic energy into the formation, measuring the energy shed back into the borehole at arbitrary sensor stations on the tool and generating resistivity signal data associated with the measured energy, and matching the signal data and the fluid resistivity against the modeled response data to determine the borehole caliper and/or formation resistivity. The apparatus forms part of a system for calculating a borehole caliper and/or the surrounding formation resistivity.

Abstract: A shield apparatus for use in conjunction with a well tool to selectively attenuate one or more electromagnetic energy field components as the components interact with the shield. The shield composed of a flexible strip or conductive body and comprising at least one sloped slot or sloped conductive element therein. The shield being adapted to surround an antenna mounted on a well tool. A method for rotating the axis of the magnetic dipole of a transmitter or receiver coil. A method for winding and shielding an electric coil such that the resultant coil emits or receives selected electromagnetic energy field components.

Abstract: A borehole tool for logging resistivity of geologic formations, having at least two inner transmitters surrounded by at least two outer receivers. Each transmitter is sequentially excited, and measurements are taken at each of the receivers. The phase differences between these received signals are determined, once for each transmitter, and the two values are averaged to estimate the resistivity value of the surrounding formations. More than two receivers can be used. An azimuthal receiver array is also used to identify boundary transitions.