Abstract: A method for signal communication between a well drilling instrument and the Earth's surface includes generating an electromagnetic field in an instrument disposed in drill string used to drill a wellbore. The electromagnetic field comprises encoded measurements from at least one sensor associated with the instrument. A signal is measured corresponding to an amplitude, phase or frequency of the electromagnetic field. The measurements are decoded from the measured signal. The measured signal comprises at least one of a voltage imparted across a capacitive electrode proximate ground surface and a galvanic electrode in contact with the ground surface, and a voltage imparted across two capacitive electrodes each proximate a ground surface and separated from each other by a known distance.

Abstract: A method for magnetic ranging includes switching an electromagnet deployed in a target wellbore between at least first and second states and acquiring a plurality of magnetic field measurements at a magnetic field sensor deployed on a drill string in a drilling wellbore while the electromagnet is switching. The magnetic field measurements may be sorted into at least first and second sets corresponding to the first and second states of the electromagnet. The first and second sets of magnetic field measurements are then processed to compute at least one of a distance and a direction from the drilling well to the target. The electromagnet may be automatically switched back and forth between the first and second states independently from the acquiring and sorting of the magnetic field measurements.

Abstract: A tool for detecting a structure in a well includes a receiver coil having a first winding and a second winding, a first circuit to apply an input signal to the second winding, and a detection circuit to detect a response of the first winding to the input signal applied to the second winding. The response of the first winding indicates presence of the structure in the well if the receiver coil is positioned proximate the structure. The depths (or locations) of these structures are used to avoid placing receivers near these structures for EM induction surveys, such as cross-well, surface-to-wellbore, or single-wellbore induction loggings with receivers in metallic casing.

Abstract: A method for signal communication between a well drilling instrument and the Earth's surface includes generating an electromagnetic field in an instrument disposed in drill string used to drill a wellbore. The electromagnetic field comprises encoded measurements from at least one sensor associated with the instrument. A signal is measured corresponding to an amplitude, phase or frequency of the electromagnetic field. The measurements are decoded from the measured signal. The measured signal comprises at least one of a voltage imparted across a capacitive electrode proximate ground surface and a galvanic electrode in contact with the ground surface, and a voltage imparted across two capacitive electrodes each proximate a ground surface and separated from each other by a known distance.

Abstract: A method for signal communication between a well drilling instrument and the Earth's surface includes generating an electromagnetic field in an instrument disposed in drill string used to drill a wellbore. The electromagnetic field includes encoded measurements from at least one sensor associated with the instrument. A signal corresponding to an amplitude of the electromagnetic field is measured and the measurements from the measured signal are decoded. The signal comprises a voltage measured across electrodes or a voltage induced in an electromagnetic receiver disposed at a selected depth below the Earth's surface. The selected depth is at least the depth of a formation below the water table having a highest resistivity within 500 meters of the surface.

Abstract: A method for signal communication between a well drilling instrument and the Earth's surface includes generating an electromagnetic field in an instrument disposed in drill string used to drill a wellbore. The electromagnetic field includes encoded measurements from at least one sensor associated with the instrument. A signal corresponding to an amplitude of the electromagnetic field is measured and the measurements from the measured signal are decoded. The signal comprises a voltage measured across electrodes or a voltage induced in an electromagnetic receiver disposed at a selected depth below the Earth's surface. The selected depth is at least the depth of a formation below the water table having a highest resistivity within 500 meters of the surface.

Abstract: A method and system for determining a geometry of a borehole includes forming an nuclear magnetic resonance (NMR) caliper with a plurality of coils and coupling the NMR caliper to a borehole assembly. The NMR caliper may be calibrated for porosity and the T2 of the drilling mud, prior to drilling, at the surface. After drilling commences, scans of the borehole may be conducted with each coil of the NMR caliper. Each scan may include propagating RF energy across a range of frequencies with each coil in order to excite a NMR signal at varying depths. Borehole wall distances from the NMR caliper may be determined by reviewing a plurality of T2 distributions from CPMG measurements derived from the scans. In some embodiments, borehole wall distances from the NMR caliper may be determined by reviewing porosity values derived from the scans.

Abstract: Methods and systems are provided that enable logging while drilling NMR measurements to be made with a tool having magnets with positions adjustable or movable relative to each other. Such movement can affect the depth of investigation of the NMR tool. A variety of moving assemblies can be used to effectuate the movement, which can be performed either at the surface or downhole. The tool also can include a magnetically permeable member to control the magnetic field gradient.

Abstract: A system and method collects at least one measurement within a borehole formed in a formation. The system and method provides a drill collar made of a non-conductive or substantially non-conductive composite material positioned within the borehole. A downhole component is capable of collecting at least one measurement and is embedded within the composite material of the drill collar. The at least one measurement collectable by the downhole component is related to the borehole or the formation about the borehole.

Abstract: A method and system for determining a geometry of a borehole includes forming an nuclear magnetic resonance (NMR) caliper with a plurality of coils and coupling the NMR caliper to a borehole assembly. The NMR caliper may be calibrated for porosity and the T2 of the drilling mud, prior to drilling, at the surface. After drilling commences, scans of the borehole may be conducted with each coil of the NMR caliper. Each scan may include propagating RF energy across a range of frequencies with each coil in order to excite a NMR signal at varying depths. Borehole wall distances from the NMR caliper may be determined by reviewing a plurality of T2 distributions from CPMG measurements derived from the scans. In some embodiments, borehole wall distances from the NMR caliper may be determined by reviewing porosity values derived from the scans.

Abstract: Impedances of an electromagnetic (EM) coil positioned in a well lined with an electrically conductive liner are determined. The impedances correspond to plural frequencies of operation of the EM coil. Based on the impedances of the EM coil corresponding to the plural frequencies, an attenuation factor associated with the electrically conductive liner is determined.

Abstract: Methods and systems are provided that enable logging while drilling NMR measurements to be made with a tool having magnets with positions adjustable or movable relative to each other. Such movement can affect the depth of investigation of the NMR tool. A variety of moving assemblies can be used to effectuate the movement, which can be performed either at the surface or downhole. The tool also can include a magnetically permeable member to control the magnetic field gradient.

Abstract: A tool for detecting a structure in a well includes a receiver coil having a first winding and a second winding, a first circuit to apply an input signal to the second winding, and a detection circuit to detect a response of the first winding to the input signal applied to the second winding. The response of the first winding indicates presence of the structure in the well if the receiver coil is positioned proximate the structure. The depths (or locations) of these structures are used to avoid placing receivers near these structures for EM induction surveys, such as cross-well, surface-to-wellbore, or single-wellbore induction loggings with receivers in metallic casing.

Abstract: Impedances of an electromagnetic (EM) coil positioned in a well lined with an electrically conductive liner are determined. The impedances correspond to plural frequencies of operation of the EM coil. Based on the impedances of the EM coil corresponding to the plural frequencies, an attenuation factor associated with the electrically conductive liner is determined.

Abstract: A downhole controller is used to tune the resonance frequency of an antenna after each NMR measurement sequence. At the end of the sequence, the downhole controller causes a pulse sequencer to generate a calibration pulse. The downhole controller then observes a voltage decay across the antenna after the calibration pulse. The downhole controller performs a Fast Fourier Transform (FFT) of the voltage decay to derive the resonant frequency of the antenna. The downhole controller determines a difference between the determined resonance frequency and the Larmor frequency and makes corresponding corrections by activating switches of the resonance tuning circuit. After each NMR measurement sequence, the downhole controller repeats the calibration to keep the antenna tuned to a frequency near the Larmor frequency.

Abstract: An NMR tool includes RF antennae and a cylindrical permanent magnet to establish a static magnetic B0 field for performing the NMR measurement sequence. The magnetic field of the magnet is polarized across the diameter of the magnet. A ferrite material is located adjacent to the permanent magnet. The antennae are located near opposite ends of the ferrite material and are formed from corresponding coils that are wound around the ferrite material such that the magnetic moments of the antennae are parallel to the longitudinal axis of the magnet.

Abstract: A method of determining the displacements of a logging tool during a measurement interval of the logging tool in a borehole includes obtaining a set of accelerometer signals corresponding to accelerations of the logging tool along each of three orthogonal axes of the logging tool during the measurement interval. The method further includes calculating a lower bound for the displacements of the logging tool during the measurement interval when the initial velocity and the gravitational acceleration are unknown. The lower bound on the displacements of the logging tool is used to flag the validity of the measurements made by the logging tool.

Abstract: An NMR logging tool includes at least one antenna and a pulse sequencer. The pulse sequencer is coupled to said at least one antenna and is adapted to receive state descriptors that are indicative of states of an NMR measurement sequence. The pulse sequencer uses the antenna(e) to perform the NMR measurement sequence downhole in a subterranean formation in response to the state descriptors.

Abstract: A downhole controller is used to tune the resonance frequency of an antenna after each NMR measurement sequence. At the end of the sequence, the downhole controller causes a pulse sequencer to generate a calibration pulse. The downhole controller then observes a voltage decay across the antenna after the calibration pulse. The downhole controller performs a Fast Fourier Transform (FFT) of the voltage decay to derive the resonant frequency of the antenna. The downhole controller determines a difference between the determined resonance frequency and the Larmor frequency and makes corresponding corrections by activating switches of the resonance tuning circuit. After each NMR measurement sequence, the downhole controller repeats the calibration to keep the antenna tuned to a frequency near the Larmor frequency.

Abstract: An NMR tool includes RF antennae and a cylindrical permanent magnet to establish a static magnetic B0 field for performing the NMR measurement sequence. The magnetic field of the magnet is polarized across the diameter of the magnet. A ferrite material is located adjacent to the permanent magnet. The antennae are located near opposite ends of the ferrite material and are formed from corresponding coils that are wound around the ferrite material such that the magnetic moments of the antennae are parallel to the longitudinal axis of the magnet.