Abstract: A system including a logging tool that can detect gamma rays in a wellbore, where the logging tool can have a window formed in an outer surface of a drill collar that allows increased sensitivity of a gamma ray detector assembly housed within the drill collar, with a body of the drill collar radially surrounding the gamma ray detector assembly, where the window can be filled with a material, and where the windows provide increased sensitivity to gamma rays in a wellbore in an azimuthal direction allowing azimuthal mapping of the gamma rays in formation surrounding the wellbore.

Abstract: A system including a logging tool that can detect gamma rays in a wellbore, where the logging tool can have a window formed in an outer surface of a drill collar that allows increased sensitivity of a gamma ray detector assembly housed within the drill collar, with a body of the drill collar radially surrounding the gamma ray detector assembly, where the window can be filled with a material, and where the windows provide increased sensitivity to gamma rays in a wellbore in an azimuthal direction allowing azimuthal mapping of the gamma rays in formation surrounding the wellbore.

Abstract: Various disclosed nuclear magnetic resonance (NMR) logging systems and methods employ an array of antennas to provide increased resolution without sacrificing signal-to-noise ratio. Certain method embodiments include: establishing a static magnetic field (B0) with a tool moving along a borehole through a formation; concurrently driving a multiple antenna cells to produce a radio frequency field (B1) in said formation; measuring an individual response from each antenna cell as nuclear spins undergo precession in the formation; and determining at least one characteristic relaxation time of the formation based at least in part on the individual response. The individual responses can be associated with positions where the individual responses were measured, and the relaxation time can be determined from a combination of those responses associated with a given position. Certain responses may be excluded due to tool motion that degrades the measured response.

Abstract: Various methods and tools optically analyze downhole fluid properties in situ. Some disclosed downhole optical radiometry tools include a tool body having a sample cell for fluid flow. A light beam passes through the sample cell and a spectral operation unit (SOU) such as a prism, filter, interferometer, or multivariate optical element (MOE). The resulting light provides a signal indicative of one or more properties of the fluid. A sensor configuration using electrically balanced thermopiles offers a high sensitivity over a wide temperature range. Further sensitivity is achieved by modulating the light beam and/or by providing a reference light beam that does not interact with the fluid flow. To provide a wide spectral range, some embodiments include multiple filaments in the light source, each filament having a different emission spectrum. Moreover, some embodiments include a second light source, sample cell, SOU, and detector to provide increased range, flexibility, and reliability.

Abstract: Logging systems and methods that employ nanosensors to obtain spectral measurements downhole. The nanosensors can be dispersed in borehole fluids (including cement slurries) that circulate, diffuse, or get injected in a borehole. Because the nanosensors have diameters on the order of 10 nm to 1000 nm, they readily penetrate into cracks, pores, and other voids where their carrier fluids can reach. The nanosensors transport light sources and recording media to measure spectra in these otherwise inaccessible regions. The nanosensors are then recovered and analyzed to reconstruct the measured spectra and determine relevant material characteristics. Among other things, spectral measurements can reveal the presence of certain elements and molecules in the formation and fluids, from which information scientists determine composition and phases of formation fluids and the formation itself.

Abstract: Various systems and methods for performing optical analysis downhole with an interferogram (a light beam having frequency components with a time variation that identifies those frequency components. The interferogram is produced by introducing an interferometer into the light path, with the two arms of the interferometer having a propagation time difference that varies as a function of time. Before or after the interferometer, the light encounters a material to be analyzed, such as a fluid sample from the formation, a borehole fluid sample, a core sample, or a portion of the borehole wall. The spectral characteristics of the material are imprinted on the light beam and can be readily analyzed by processing electronics that perform a Fourier Transform to obtain the spectrum or that enable a comparison with one or more templates. An interferometer designed to perform well in the hostile environments downhole is expected to enable laboratory-quality measurements.

Abstract: Various disclosed nuclear magnetic resonance (NMR) logging systems and methods employ an array of antennas to provide increased resolution without sacrificing signal-to-noise ratio. Certain method embodiments include: establishing a static magnetic field (B0) with a tool moving along a borehole through a formation; concurrently driving a multiple antenna cells to produce a radio frequency field (B1) in said formation; measuring an individual response from each antenna cell as nuclear spins undergo precession in the formation; and determining at least one characteristic relaxation time of the formation based at least in part on the individual response. The individual responses can be associated with positions where the individual responses were measured, and the relaxation time can be determined from a combination of those responses associated with a given position. Certain responses may be excluded due to tool motion that degrades the measured response.

Abstract: Logging systems and methods that employ nanosensors to obtain spectral measurements downhole. The nanosensors can be dispersed in borehole fluids (including cement slurries) that circulate, diffuse, or get injected in a borehole. Because the nanosensors have diameters on the order of 10 nm to 1000 nm, they readily penetrate into cracks, pores, and other voids where their carrier fluids can reach. The nanosensors transport light sources and recording media to measure spectra in these otherwise inaccessible regions. The nanosensors are then recovered and analyzed to reconstruct the measured spectra and determine relevant material characteristics. Among other things, spectral measurements can reveal the presence of certain elements and molecules in the formation and fluids, from which information scientists determine composition and phases of formation fluids and the formation itself.

Abstract: Various systems and methods for performing optical analysis downhole with an interferogram (a light beam having frequency components with a time variation that identifies those frequency components. The interferogram is produced by introducing an interferometer into the light path, with the two arms of the interferometer having a propagation time difference that varies as a function of time. Before or after the interferometer, the light encounters a material to be analyzed, such as a fluid sample from the formation, a borehole fluid sample, a core sample, or a portion of the borehole wall. The spectral characteristics of the material are imprinted on the light beam and can be readily analyzed by processing electronics that perform a Fourier Transform to obtain the spectrum or that enable a comparison with one or more templates. An interferometer designed to perform well in the hostile environments downhole is expected to enable laboratory-quality measurements.

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: 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: Method and apparatus are provided to accelerate the cooling of thermally sensitive components in a chamber of a downhole instrument assembly. In accordance with the invention, a passage is formed in the chamber and a fluid is conveyed through the passage to cool the components to the desired temperature. By using the method and apparatus of the present invention the amount of time to cool the components is dramatically less than the time required for cooling using conventional techniques.