Abstract: A drill string can include at least one transmit antenna and at least one receive antenna. The transmit antenna transmits at least one electromagnetic signal into a region of an earth formation. The receive antenna receives the signal from the region of the earth formation. The transmit antenna comprises one of a magnetic dipole and an electric dipole, and the receive antenna comprises the other of the magnetic dipole and the electric dipole. At least one characteristic of the region of the earth formation is determined, based at least partially on the signal received by the receive antenna. A homogeneous part of the electromagnetic signal may be reduced, to thereby increase a depth of detection of the characteristic.

Abstract: Disclosed herein are electromagnetic resistivity logging systems and methods that employ magnetic dipole antennas embedded in wall-contacting surfaces. In some embodiments, the antennas are pot-core or ferrite-rod antennas. Prototypes of electromagnetic resistivity logging tools having such antennas exhibit good resistivity logging performance in both water-based and oil-based borehole fluids, indicating that this architecture may yield a logging tool that is suitable for use with borehole fluids of all types. Moreover, the tool offers good spatial resolution, enabling the creation of formation resistivity images for the borehole walls.

Abstract: Various embodiments include apparatus and methods to operate a tool downhole in a well, where the tool has an optical computation element to determine different properties of downhole structures. Such an optical computation element can be structured to provide optical analysis of fluid and material composition of the downhole environment associated with a drilling operation. The data measurements from the optical computation element can be used in a geosteering operation. Additional apparatus, systems, and methods are disclosed.

Abstract: A drill string can include at least one transmit antenna and at least one receive antenna. The transmit antenna transmits at least one electromagnetic signal into a region of an earth formation. The receive antenna receives the signal from the region of the earth formation. The transmit antenna comprises one of a magnetic dipole and an electric dipole, and the receive antenna comprises the other of the magnetic dipole and the electric dipole. At least one characteristic of the region of the earth formation is determined, based at least partially on a first signal as received by the receive antenna at a first time, a second signal as received by the receive antenna at a second time, and a distance traveled by the drill string between the first and the second times. A homogeneous part of the electromagnetic signal may be reduced, to thereby increase a depth of detection of the characteristic.

Abstract: A formation core analysis system can include an inner barrel and a toroidal electromagnetic antenna which transmits electromagnetic signals into a formation core when the core is received in the inner barrel. Another formation core analysis system can include an inner barrel and multiple longitudinally spaced apart electrodes which electrically contact a formation core when the core is received in the inner barrel. A speed of displacement of the core into the inner barrel may be indicated by differences between measurements taken via the electrodes as the core displaces into the inner barrel. A method of measuring resistivity of a formation core as the core is being cut can include transmitting electromagnetic signals into the core from a toroidal electromagnetic antenna as the core is being cut by a coring bit.

Abstract: Nearby conductors such as pipes, well casing, etc., are detectable from within a borehole filled with an oil-based fluid. At least some method embodiments provide a current flow between axially-spaced conductive bridges on a drillstring. The current flow disperses into the surrounding formation and causes a secondary current flow in the nearby conductor. The magnetic field from the secondary current flow can be detected using one or more azimuthally-sensitive antennas. Direction and distance estimates are obtainable from the azimuthally-sensitive measurements, and can be used as the basis for steering the drillstring relative to the distant conductor. Possible techniques for providing current flow in the drillstring include imposing a voltage across an insulated gap or using a toroid around the drillstring to induce the current flow.

Abstract: Various embodiments include apparatus and methods of operation with respect to well logging. Apparatus and methods can include a tool having an arrangement of spaced apart transmitter antennas and receiver antennas in transmitter-receiver antenna pairs to make shallow measurements and deep measurements. The signals acquired from the shallow measurements and deep measurements can be processed to provide a look-ahead signal in a drilling operation. The transmitter and receiver antennas can be oriented to cancel or substantially cancel out signals from layers between the transmitter antenna and the receiver antenna in response to the transmitter being operated downhole in a well. Additional apparatus, systems, and methods are disclosed.

Abstract: Various embodiments include apparatus and methods to detect and locate conductive structures below the earth's surface. Tools can be configured with receiving sensors arranged to receive signals generated from a conductive structure in response to a current flowing on the conductive structure. Magnetic-related values from the signals can be processed, relative to the tool, to determine a position of a conductive structure from which the signal was generated in response to current flowing on the conductive structure. Additional apparatus, systems, and methods are disclosed.

Abstract: A method and system to compensate for inaccuracies in crosswell tomography is presented. The method includes obtaining data from at least two receivers in response to transmissions from at least two transmitters. Next, at least one compensated value is derived based on the responses of the receivers to the transmitters. Finally, an inversion is performed based at least in part on the compensated value derived. This method eliminates inaccuracies that can be caused by sensor gain and phase variations in the inversion process. Inversion results with gain and phase compensation produce better imaging results that can better help determine the shape and boundaries of the reservoir.

Abstract: One method of monitoring a formation core during coring operations can include measuring resistivities of a formation internal and external to a core barrel assembly, comparing the resistivities of the formation internal and external to the core barrel assembly, and determining a displacement of the core into the core barrel assembly, based at least in part on the comparing, while the core is being cut. A formation core analysis system can include multiple longitudinally spaced apart sets of transmitters and receivers which measure resistivity of a core while the core displaces into a core barrel assembly, and multiple longitudinally spaced apart sets of transmitters and receivers which measure resistivity of a formation external to the core barrel assembly while a coring bit penetrates the formation. A speed of displacement of the core may be indicated by differences in time between measurements taken via the different sets as the core displaces.

Abstract: Methods and tools for detecting casing position downhole is presented. The method utilizes electromagnetic. (EM) tools with tilted antenna systems to detect casing position. Sometimes titled antenna designs also increase EM tools' sensitivity to formation parameters, which can lead to false signals for casing detection. In addition, it is very difficult to distinguish measured signals between a casing source and a formation source. The methods presented help to distinguish between the two sources more clearly. The methods and tools presented also help to minimize those environmental effects, as well as enhance the signals from a surrounding conductive casing. The methods herein provide ideas of EM tool's design to precisely determine casing position within a certain distance to casing position.

Abstract: Various embodiments include apparatus and methods to detect and locate conductive structures below the earth's surface. Tools can be configured with receiving sensors arranged to receive signals generated from a conductive structure in response to a current flowing on the conductive structure. Magnetic-related values from the signals can be processed, relative to the tool, to determine a position of a conductive structure from which the signal was generated in response to current flowing on the conductive structure. Additional apparatus, systems, and methods are disclosed.

Abstract: Methods and apparatus for detecting nearby conductors such as pipes, well casing, etc., from within a borehole. A nearby casing string can be detected by transmitting an electromagnetic signal from a first antenna on a downhole logging tool and measuring a response signal with a second antenna. As the tool rotates, the transmitting and measuring are repeated to determine the azimuthal dependence of the response signal. The azimuthal dependence is analyzed to determine an diagonal component and a cross component. The amplitude of the diagonal component is indicative of distance to the conductive feature. Direction can be determined based on the diagonal component alone or in combination with the cross component. Sinusoidal curve fitting can be employed to improve accuracy of the distance and direction estimates. At least one of the antennas is preferably tilted. Measurement results are presented for parallel tilted and perpendicular tilted antennas.

Abstract: Disclosed herein are multicomponent borehole radar tools and methods. At least some tool embodiments employ at least two antennas that receive reflections of electromagnetic pulses transmitted from the tool. A processor processes the receive signals to identify reflection signals and to determine a direction and/or distance to the sources of the reflection signals. Possible sources include formation boundaries, fluid boundaries, cased wells, and other features that cause contrasts in electromagnetic properties. In addition to reflection signals, the measured responses may include direct signal measurements that are useful for determining formation resistivity and permittivity. Each of the antennas may transmit and receive, and they may be collocated to reduce tool size and reduce processing complexity. Disclosed logging tool examples employ both electric and magnetic dipole antennas.

Abstract: Systems and methods are disclosed for reducing boundary-related artifacts in logs taken from resistivity logging tools. Such tools often exhibit “horns” at boundaries between formation beds having different resistivities. A boundary indicator signal serves to identify the location of these boundaries. When derived from an azimuthally-sensitive resistivity tool, the bed boundary indicator may have a magnitude and shape that serves to nearly eliminate the horns even in high-dip angle environments. Logs that are processed to eliminate these artifacts are expected to be more accurate and thus easier to interpret.

Abstract: Various embodiments include apparatus and methods to operate an induction measurement process in a borehole that addresses direct coupling of a signal between sensors of a measuring tool. Apparatus and methods can include a processing unit to generate formation parameters from signals received in the measurement tool. Additional apparatus, systems, and methods are disclosed.

Abstract: Logging tools and methods employing an at-bit loop antenna to acquire azimuthal resistivity measurements proximate to the bit enable low-latency geosteering signals to be generated. In some embodiments, the at-bit antenna is part of a bottom hole assembly that includes a drill bit, a mud motor, and a resistivity tool. The mud motor is positioned between the at-bit antenna and the resistivity tool. The resistivity tool includes at least one loop antenna that is not parallel to the at-bit loop antenna. The at-bit antenna is part of an at-bit module that, in some embodiments, transmits periodic electromagnetic signal pulses for the resistivity tool to measure. In other embodiments, the at-bit module measures characteristics of electromagnetic signal pulses sent by the resistivity tool and communicates the measured characteristics to the resistivity tool via a short hop telemetry link.

Abstract: Multi-array laterolog tool systems and methods acquire a set of array measurements sufficient to provide laterolog tool measurements of differing array sizes. Such systems and method offer multiple depths of investigation while offering greater measurement stability in borehole environments having high resistivity contrasts. In at least some system embodiments, a wireline or LWD tool body has a center electrode positioned between multiple pairs of guard electrodes and a pair of return electrodes. The tool's electronics provide a current from the center electrode to the pair of return electrodes and currents from each pair of guard electrodes to the pair of return electrodes. Each of the currents may be distinguishable by frequency or distinguishable by some other means. This novel arrangement of currents provides a complete set of measurements that enables one tool to simultaneously emulate a whole range of laterolog tools.

Abstract: Various embodiments include apparatus and methods to land a well in a target zone with minimal or no overshoot of target zone. The well may be directed to a target in the target zone based on the separation distance between a transmitter sensor (212) and a receiver sensor (214) being sufficiently large to detect a boundary of the target zone from a distance from the boundary of the target zone such that collected received signals from activating the transmitter sensor (212) can be processed in a time that provides minimal or no overshoot of a target zone. Additional apparatus, systems, and methods are disclosed.

Abstract: Multi-array laterolog tool systems and methods acquire a set of array measurements sufficient to provide laterolog tool measurements of differing array sizes. Such systems and method offer multiple depths of investigation while offering greater measurement stability in borehole environments having high resistivity contrasts. In at least some system embodiments, a wireline or LWD tool body has a center electrode positioned between multiple pairs of guard electrodes and a pair of return electrodes. The tool's electronics provide a current from the center electrode to the pair of return electrodes and currents from each pair of guard electrodes to the pair of return electrodes. Each of the currents may be distinguishable by frequency or distinguishable by some other means. This novel arrangement of currents provides a complete set of measurements that enables one tool to simultaneously emulate a whole range of laterolog tools.