Abstract: A system for performing downhole logging operations includes a conductor coil configured to alternate between producing a magnetic field and measuring a magnetic field induced in a formation, a power supply couplable to the conductor coil for providing an electrical control current to conductor coil, and a signal acquisition system couplable to the conductor coil. The system further includes a permanent magnet coupled to the conductor coil, and a multi-state switch operable in a first state and a second state. In the first state, the conductor coil is coupled to an output of the power supply and decoupled from an input of the signal acquisition system. In the second state, the conductor coil is coupled to the input of acquisition electronics and decoupled from the output of the power supply.

Abstract: A resistivity imaging device and a method of operating the resistivity imaging device in a wellbore. The resistivity imaging device includes a first electrode, a second electrode, and a circuit electrically coupled to the first electrode and the second electrode. An impedance is measured of a formation surrounding the wellbore. Based on the impedance, the circuit is configured into one of a first circuit configuration for operating the resistivity imaging device in a first mode and a second circuit configuration for operating the resistivity imaging device in a second mode. The resistivity imaging device is operated using the circuit in the one of the first circuit configuration and the second circuit configuration.

Abstract: A device for generating oscillating signals includes an energy transfer device configured to apply an oscillating signal to a sensitive volume, and a resonant tuning circuit including the energy transfer device. The tuning circuit includes a tuning capacitor configured to cause the tuning circuit to resonate at a selected frequency, and an energy storage device. The transmitting device also includes a controller configured to apply a pulse sequence to the tuning circuit having a series of pulses, the energy storage device configured to retain electrical energy at an end of a first pulse, and discharge the electrical energy to the tuning circuit at an onset of a next pulse of the pulse sequence.

Abstract: A resistivity imaging device and a method of operating the resistivity imaging device in a wellbore. The resistivity imaging device includes a first electrode, a second electrode, and a circuit electrically coupled to the first electrode and the second electrode. An impedance is measured of a formation surrounding the wellbore. Based on the impedance, the circuit is configured into one of a first circuit configuration for operating the resistivity imaging device in a first mode and a second circuit configuration for operating the resistivity imaging device in a second mode. The resistivity imaging device is operated using the circuit in the one of the first circuit configuration and the second circuit configuration.

Abstract: Methods and logging systems for performing nuclear magnetic resonance (NMR) logging in downhole operations are described. The methods include performing a scout logging acquisition operation using an NMR logging tool to determine NMR logging parameters of a formation interval, setting an NMR logging acquisition mode based on the NMR logging parameters from the scout logging acquisition operation, and performing an NMR data logging operation to determine properties of the formation interval based on the set NMR logging acquisition mode.

Abstract: A device for generating oscillating signals includes an energy transfer device configured to apply an oscillating signal to a sensitive volume, and a resonant tuning circuit including the energy transfer device. The tuning circuit includes a tuning capacitor configured to cause the tuning circuit to resonate at a selected frequency, and an energy storage device. The transmitting device also includes a controller configured to apply a pulse sequence to the tuning circuit having a series of pulses, the energy storage device configured to retain electrical energy at an end of a first pulse, and discharge the electrical energy to the tuning circuit at an onset of a next pulse of the pulse sequence.

Abstract: An apparatus for performing a nuclear magnetic resonance (NMR) measurement in a borehole penetrating a subsurface formation includes an NMR tool having an outside diameter that is less than an inside diameter of a drill tubular disposed in the borehole, the drill tubular having an opening at the distal end of the drill tubular leading into the borehole, and a retaining device configured to allow at least a section of the NMR tool to protrude through the opening of the drill tubular and prevent an unrestrained release of the NMR tool through the opening. The apparatus also includes a transmitter antenna and a receiver antenna coupled to the NMR tool, wherein the transmitter antenna and/or the receiver antenna are extendable from the NMR tool.

Abstract: Methods and logging systems for performing nuclear magnetic resonance (NMR) logging in downhole operations are described. The methods include performing a scout logging acquisition operation using an NMR logging tool to determine NMR logging parameters of a formation interval, setting an NMR logging acquisition mode based on the NMR logging parameters from the scout logging acquisition operation, and performing an NMR data logging operation to determine properties of the formation interval based on the set NMR logging acquisition mode.

Abstract: An apparatus for performing a nuclear magnetic resonance (NMR) measurement in a borehole penetrating a subsurface formation includes an NMR tool having an outside diameter that is less than an inside diameter of a drill tubular disposed in the borehole, the drill tubular having an opening at the distal end of the drill tubular leading into the borehole, and a retaining device configured to allow at least a section of the NMR tool to protrude through the opening of the drill tubular and prevent an unrestrained release of the NMR tool through the opening. The apparatus also includes a transmitter antenna and a receiver antenna coupled to the NMR tool, wherein the transmitter antenna and/or the receiver antenna are extendable from the NMR tool.

Abstract: An NMR measurement apparatus includes a transmitting antenna including a transmitter coil, a capacitor, a dissipating component and a restricting component, and a receiving antenna physically separated from the transmitting antenna. A processor is configured to apply a drive signal at a first voltage level to generate a transmission signal having a selected transmission frequency, where the receiving antenna is deactivated during generation, connect the dissipating component to the transmitter coil to dissipate stored energy in the transmitter coil, connect the restricting component to the transmitter coil to restrict the transmitting antenna to a second voltage level smaller than the first voltage level and based on a voltage of NMR signals from the sensitive volume, activate the receiving antenna and detect a NMR signal, where the restricting component is connected to the transmitter coil and restricts the transmitting antenna during the activating and the detecting.

Abstract: An example method includes disposing a carrier in a borehole in an earth formation. The carrier includes a logging assembly for performing a formation evaluation of the earth formation using a sensor in proximity to a borehole wall of the borehole, fluid being disposed at least partially between the sensor and the borehole wall. The method further includes estimating an apparent dielectric loss angle of the fluid to determine a stand-off effect caused by the fluid. The method further includes estimating a formation dielectric loss angle and determining a formation resistance based at least in part on the formation dielectric loss angle. The method further includes adjusting the formation evaluation based at least in part on the estimated formation resistance that accounts for the stand-off effect caused by the fluid. The method further includes performing a wellbore operation based at least in part on the adjusted formation evaluation.

Abstract: A downhole electrical logging tool includes a mandrel, and a pad coupled to and radially extendable from the mandrel. The pad includes an isolated power supply configured to receive DC or AC power via the mandrel and convert the DC or AC power into one or more DC voltages for powering electronic components on the pad. The pad further includes a digital data processor (e.g., a microcontroller, field programmable gate array, or digital signal processor) powered by the isolated power supply, a transmitter electrode, and a sensing electrode. The pad also includes a housing in which the controller and isolated power supply are located, and a pad body coupled to the mandrel. Components inside the housing are electrically isolated from the pad body. The tool further includes a signal generator electrically coupled to the transmitter electrode to drive the transmitter electrode.

Abstract: A system for performing downhole logging operations includes a conductor coil configured to alternate between producing a magnetic field and measuring a magnetic field induced in a formation, a power supply couplable to the conductor coil for providing an electrical control current to conductor coil, and a signal acquisition system couplable to the conductor coil. The system further includes a permanent magnet coupled to the conductor coil, and a multi-state switch operable in a first state and a second state. In the first state, the conductor coil is coupled to an output of the power supply and decoupled from an input of the signal acquisition system. In the second state, the conductor coil is coupled to the input of acquisition electronics and decoupled from the output of the power supply.

Abstract: A system for performing downhole logging operations includes a power supply for providing a current and a conductor coil electrically coupled to receive the current from the power supply. The system further includes a switch electrically coupled to the power supply for controlling current provided to the conductor coil and enabling a pulse of current to be supplied to the conductor coil for an “on” duration and turning off current provided to the conductor coil for an “off” duration after the “on” duration, in which the “off” duration lasts longer than the “on” duration. The system also includes a permanent magnet coupled to the conductor coil. The conductor coil receives the pulse of current from the power supply during the “on” duration and not receiving current during the “off” duration. The pulse of current causes the permanent magnet to reverse polarity and generate a transient magnetic field.

Abstract: An example method includes disposing a carrier in a borehole in an earth formation. The carrier includes a logging assembly for performing a formation evaluation of the earth formation using a sensor in proximity to a borehole wall of the borehole, fluid being disposed at least partially between the sensor and the borehole wall. The method further includes estimating an apparent dielectric loss angle of the fluid to determine a stand-off effect caused by the fluid. The method further includes estimating a formation dielectric loss angle and determining a formation resistance based at least in part on the formation dielectric loss angle. The method further includes adjusting the formation evaluation based at least in part on the estimated formation resistance that accounts for the stand-off effect caused by the fluid. The method further includes performing a wellbore operation based at least in part on the adjusted formation evaluation.

Abstract: Systems, devices, and methods for estimating a value of a downhole parameter of interest. Aspects include an apparatus for evaluating a tubular. The apparatus may include a sensor including an electromagnetic acoustic transducer (EMAT) device configured to be conveyed into the tubular. The EMAT device may include measurement circuitry comprising at least one conductive coil; and a magnet array comprising magnets arranged with a corresponding direction of magnetization of each magnet oriented according to a configuration producing a greater magnetic flux on a first side of the array than on a second side opposing the first side. The magnetic flux produced from the second side may be substantially zero. In embodiments, the configuration of magnets comprises at least a first set of permanent magnets in a linear Halbach configuration.

Abstract: Systems, devices, and methods for estimating a value of a downhole parameter of interest. Aspects include an apparatus for evaluating a tubular. The apparatus may include a sensor including an electromagnetic acoustic transducer (EMAT) device configured to be conveyed into the tubular. The EMAT device may include measurement circuitry comprising at least one conductive coil; and a magnet array comprising magnets arranged with a corresponding direction of magnetization of each magnet oriented according to a configuration producing a greater magnetic flux on a first side of the array than on a second side opposing the first side. The magnetic flux produced from the second side may be substantially zero. In embodiments, the configuration of magnets comprises at least a first set of permanent magnets in a linear Halbach configuration.

Abstract: Methods and apparatus configured to evaluate a volume of interest of an earth formation intersected by a borehole. Apparatus comprise a transceiver electrode on the tool body configured to provide electrical current to the earth formation; a return electrode configured to receive the electrical current returning from the earth formation; a multi-function electrode on the resistivity imager tool; and an electrical system configured to provide current measurements at the transceiver electrode. In the first operational mode, the electrical system maintains the tool body at a first electrical potential, and maintains the multi-function electrode and the transceiver electrode at a second electrical potential; and in the second operational mode, the electrical system maintains the tool body at the first electrical potential, maintains the multi-function electrode at the first electrical potential, and maintains the transceiver electrode at the second potential.

Abstract: Methods and apparatus configured to evaluate a volume of interest of an earth formation intersected by a borehole. Apparatus comprise a transceiver electrode on the tool body configured to provide electrical current to the earth formation; a return electrode configured to receive the electrical current returning from the earth formation; a multi-function electrode on the resistivity imager tool; and an electrical system configured to provide current measurements at the transceiver electrode. In the first operational mode, the electrical system maintains the tool body at a first electrical potential, and maintains the multi-function electrode and the transceiver electrode at a second electrical potential; and in the second operational mode, the electrical system maintains the tool body at the first electrical potential, maintains the multi-function electrode at the first electrical potential, and maintains the transceiver electrode at the second potential.

Abstract: A method and system for measuring formation resisitivity is achieved by introducing an electrical signal into the formation. The current of the introduced electrical signal is then sensed, producing an analog voltage signal as a measurement of the formation. The introduced electrical signal is compared with the measured signal of the formation. The comparison is made in a quadrature demodulation device, producing an in-phase demodulated signal. A quasi-direct-current signal is extracted from the in-phase demodulated signal, producing an analog measurement related to the resistivity of the formation.