Abstract: A downhole tool, in some embodiments, comprises a casing collar locator (CCL) to generate a signal that indicates the presence of a casing discontinuity; and a modulator, coupled to the CCL, to modulate fixed-wavelength light in a fiber optic cable based on said signal.

Abstract: A disclosed subsurface detection system includes a first communication device positioned in a borehole and configured to scan a plurality of frequencies in at least a portion of an annulus surrounding an exterior of a tubing including the casing string in the borehole or an interior of the tubing including the casing string. The plurality of frequencies include a first frequency corresponding to a first type of RFID tag and a second frequency corresponding to a second type of RFID tag. The first communication device is further configured to detect a response to the scan from an RFID tag of the first type or the second type in the portion of the annulus or the interior of the tubing. The system further includes a processor configured to receive communication of the detected response from the first communication device, and based on the detected response, determine one or more characteristics of an environment around the corresponding RFID tag (e.g.

Abstract: Switchable multi-antenna fluid sensing systems and methods, including a tubular-mounted switchable multi-antenna fluid sensing system that includes two antenna arrays that each senses fluid characteristics not sensed by other antenna arrays, each array including multiple antenna sub-arrays and each sub-array including a receive and transmit antenna with a radial transmission direction different from that of other sub-arrays. The system also includes two RF multiplexers, each coupled to the antennas within the arrays and to corresponding RF transceivers within a sensor tube. A CPU within the sensor tube couples to the RF transceivers, controls signal transmission by, and processes received signals from, the antennas. RF cables coupling the RF transceivers and RF multiplexers are grouped and routed through one end of the sensor tube. The CPU further causes the RF multiplexers to periodically couple to the antennas and stores and/or transmits data representing the received signals.

Abstract: A disclosed subsurface detection system includes a first communication device positioned in a borehole and configured to scan a plurality of frequencies in at least a portion of an annulus surrounding an exterior of a tubing including the casing string in the borehole or an interior of the tubing including the casing string. The plurality of frequencies include a first frequency corresponding to a first type of RFID tag and a second frequency corresponding to a second type of RFID tag. The first communication device is further configured to detect a response to the scan from an RFID tag of the first type or the second type in the portion of the annulus or the interior of the tubing. The system further includes a processor configured to receive communication of the detected response from the first communication device, and based on the detected response, determine one or more characteristics of an environment around the corresponding RFID tag (e.g.

Abstract: A downhole tool, in some embodiments, comprises a casing collar locator (CCL) to generate a signal that indicates the presence of a casing discontinuity; and a modulator, coupled to the CCL, to modulate fixed-wavelength light in a fiber optic cable based on said signal.

Abstract: Systems and methods are provided for generating a phase compensated numerically controlled signal using a fixed-point algorithm. In one example, a method includes receiving, at a downhole device, parameters including an input frequency and a compensation value. The method further includes converting, based on the parameters, the input frequency to a delta phase value. The method also includes calculating, with the downhole device, an accumulation error for a digital signal. In response to determining that the accumulation error is greater than or equal to the compensation value, the method removes the accumulation error from the digital signal to generate an output signal.

Abstract: Switchable multi-antenna fluid sensing systems and methods, including a tubular-mounted switchable multi-antenna fluid sensing system that includes two antenna arrays that each senses fluid characteristics not sensed by other antenna arrays, each array including multiple antenna sub-arrays and each sub-array including a receive and transmit antenna with a radial transmission direction different from that of other sub-arrays. The system also includes two RF multiplexers, each coupled to the antennas within the arrays and to corresponding RF transceivers within a sensor tube. A CPU within the sensor tube couples to the RF transceivers, controls signal transmission by, and processes received signals from, the antennas. RF cables coupling the RF transceivers and RF multiplexers are grouped and routed through one end of the sensor tube. The CPU further causes the RF multiplexers to periodically couple to the antennas and stores and/or transmits data representing the received signals.

Abstract: Systems and methods are provided for generating a phase compensated numerically controlled signal using a fixed-point algorithm. In one example, a method includes receiving, at a downhole device, parameters including an input frequency and a compensation value. The method further includes converting, based on the parameters, the input frequency to a delta phase value. The method also includes calculating, with the downhole device, an accumulation error for a digital signal. In response to determining that the accumulation error is greater than or equal to the compensation value, the method removes the accumulation error from the digital signal to generate an output signal.

Abstract: In one aspect, a resistivity logging tool for a fluid-producing formation if provided. The resistivity logging tool includes at least one transmitter device connected to at least one excitation electrode, multiple receiver devices respectively connected to monitoring electrodes, and a controller. The transmitter can inject an excitation current into the formation via the excitation electrode. Each receiver device can determine a respective voltage level induced by the excitation current. The controller can determine whether a voltage level measured by at least one receiver device is within a specified range. Based on the measured voltage level, the controller can select a global amplitude adjustment algorithm for modifying excitation currents or a localized amplitude adjustment algorithm for modifying one or more gains of one or more receiver devices. The controller can modify the excitation current or gains by executing the selected algorithm.

Abstract: In one aspect, a resistivity logging tool for a fluid-producing formation if provided. The resistivity logging tool includes at least one transmitter device connected to at least one excitation electrode, multiple receiver devices respectively connected to monitoring electrodes, and a controller. The transmitter can inject an excitation current into the formation via the excitation electrode. Each receiver device can determine a respective voltage level induced by the excitation current. The controller can determine whether a voltage level measured by at least one receiver device is within a specified range. Based on the measured voltage level, the controller can select a global amplitude adjustment algorithm for modifying excitation currents or a localized amplitude adjustment algorithm for modifying one or more gains of one or more receiver devices. The controller can modify the excitation current or gains by executing the selected algorithm.

Abstract: An apparatus and method for minimizing the effects of a common mode voltage signal in downhole logging tools utilized to determine the resistivity of an adjacent portion of a borehole wall. Two current electrodes are energized by an excitation source to create an oscillatory electric field in a borehole wall. A voltage drop across a segment of the borehole wall is measured by two voltage electrodes, and the differential voltage is used in combination with a measured current flow to determine a resistivity value for the borehole wall. A common mode voltage in front of the two voltage electrodes is measured and minimized by controlling the excitation source, thereby reducing the resistivity measurement error.

Abstract: Oil-based mud imaging systems and methods having leakage current compensation. In some embodiments, disclosed logging systems include a logging tool in communication with surface computing facilities. The logging tool is provided with a sensor array having at least two voltage electrodes positioned between at least two current electrodes that create an electric field in a borehole wall, and is further provided with electronics coupled to the current electrodes to determine a differential voltage between the voltage electrodes in response to different current frequencies from the current electrodes. From the voltage measurements at different frequencies, the computing facilities determine borehole wall resistivity as a function of depth and azimuth, and may display the resistivity as a borehole wall image.

Abstract: Oil-based mud imaging systems and methods that measure formation permittivity. In some embodiments, disclosed logging systems include a logging tool in communication with surface computing facilities. The logging tool is provided with a sensor array having at least two voltage electrodes positioned between at least two current electrodes that create an electric field in a borehole wall, and is further provided with electronics coupled to the voltage electrodes to determine a differential voltage magnitude and phase. From the magnitude and phase, formation resistivity and permittivity measurements can be determined and used to construct a borehole wall image.

Abstract: An apparatus and method for minimizing the effects of a common mode voltage signal in downhole logging tools utilized to determine the resistivity of an adjacent portion of a borehole wall. Two current electrodes are energized by an excitation source to create an oscillatory electric field in a borehole wall. A voltage drop across a segment of the borehole wall is measured by two voltage electrodes, and the differential voltage is used in combination with a measured current flow to determine a resistivity value for the borehole wall. A common mode voltage in front of the two voltage electrodes is measured and minimized by controlling the excitation source, thereby reducing the resistivity measurement error.

Abstract: An apparatus and method for minimizing the effects of a common mode voltage signal in downhole logging tools utilized to determine the resistivity of an adjacent portion of a borehole wall. Two current electrodes are energized by an excitation source to create an oscillatory electric field in a borehole wall. A voltage drop across a segment of the borehole wall is measured by two voltage electrodes, and the differential voltage is used in combination with a measured current flow to determine a resistivity value for the borehole wall. A common mode voltage in front of the two voltage electrodes is measured and minimized by controlling the excitation source, thereby reducing the resistivity measurement error.

Abstract: Oil-based mud imaging systems and methods having standoff compensation. In some embodiments, disclosed logging systems include a logging tool in communication with surface computing facilities. The logging tool is provided with a sensor array having at least two voltage electrodes positioned between two current electrodes energized by an excitation source to create an oscillatory electric field in a borehole wall. The two current electrodes are each shielded with conductive shields to prevent current leakage into the logging tool body. A common mode voltage is measured, and the phase and amplitude of the excitation source is controlled to reduce the difference between the common mode voltage and reference voltage of a voltage detector. The logging tool is further provided with electronics coupled to the voltage detector and the current electrodes to determine a differential voltage between the voltage electrodes and two current flows from separate ones of the current electrodes.

Abstract: Oil-based mud imaging systems and methods that measure formation permittivity. In some embodiments, disclosed logging systems include a logging tool in communication with surface computing facilities. The logging tool is provided with a sensor array having at least two voltage electrodes positioned between at least two current electrodes that create an electric field in a borehole wall, and is further provided with electronics coupled to the voltage electrodes to determine a differential voltage magnitude and phase. From the magnitude and phase, formation resistivity and permittivity measurements can be determined and used to construct a borehole wall image.

Abstract: Oil-based mud imaging systems and methods having leakage current compensation. In some embodiments, disclosed logging systems include a logging tool in communication with surface computing facilities. The logging tool is provided with a sensor array having at least two voltage electrodes positioned between at least two current electrodes that create an electric field in a borehole wall, and is further provided with electronics coupled to the current electrodes to determine a differential voltage between the voltage electrodes in response to different current frequencies from the current electrodes. From the voltage measurements at different frequencies, the computing facilities determine borehole wall resistivity as a function of depth and azimuth, and may display the resistivity as a borehole wall image.