Abstract: Methods, systems, and computer program products for identifying annular space materials calculate a near-to-far (“N/F”) neutron count ratio from neutron count rates detected by detectors located near to and far from a neutron source, respectively. The N/F neutron count ratio may then be used along with formation porosity to provide an estimation of the type of material that may be present in the annular space.

Abstract: In some embodiments, methods, apparatus, and systems may operate to determine downhole tool standoff using a nuclear tool and photon activity, and to correct acoustic measurements using the standoff.

Abstract: A method and system for evaluating the cement behind casing and fully inverting acoustic properties of the material, including density and the speed of sound. A density map of the cement sheath is determined using a nuclear logging technique. An acoustic impedance value of the cement sheath is provided, either by measurement using an ultrasonic logging technique or simulated using an acoustic model. The acoustic model may assume a vertical incident plane wave and flat plates for casing and the cement sheath. From the density map and the acoustic impedance value, a map of the speed of sound in the cement sheath, or a gap therein, may be determined.

Abstract: Disclosed are apparatus, systems, and methods for determining the completeness of the cement sheath or gravel-pack annulus of a borehole based on gamma counts or count rates measured with a pulsed neuron tool deployed in the borehole in conjunction with a quantitative relationship between certain gamma count (rate) ratios and a parameter of completeness. In various embodiments, the determination utilizes the ratio of the net long inelastic count (rate) and the near capture count (rate), or the ratio of the net near inelastic count (rate) and the long capture count (rate). Additional apparatus, systems, and methods are disclosed.

Abstract: A gamma-ray spectrometer calibration system comprises a light guide, a photomultiplier tube, a laser, and analysis electronics. The light guide is optically coupled to the scintillation crystal, the laser and the photomultiplier tube, such that the laser can provide reference signals to the photomultiplier tube. In some embodiments, one or more temperature sensors are provided, such that the analysis electronics determine initial settings and adjust the initial settings based on the temperatures measured by the temperature sensors. Additional apparatus, methods, and systems are disclosed.

Abstract: In relation to a cut and pull operation, a nuclear tool may be used for evaluating the composition of materials located behind a pipe lining the wellbore. More specifically, a downhole method may include emitting gamma rays into the pipe and the material from a source of a nuclear tool disposed in the wellbore; detecting gamma radiation scattered back from the pipe and the material with a detector of the nuclear tool; determining a high-energy range and a low-energy range for the gamma radiation; measuring count rates of the gamma radiation in the high-energy range (CRH) and the low-energy range (CRL); performing an analysis of (1) the CRH relative to (2) the CRL; and determining a compositional equivalent for the material based on the analysis.

Abstract: Various embodiments include systems and methods to provide a pulsed chemical neutron source. The pulsed chemical neutron source can be used in well logging applications. Apparatus can be arranged to generate neutrons from a chemical neutron emitter and to pass the neutrons through an aperture of a neutron shield when the chemical neutron emitter aligns with the aperture such that the neutrons are substantially blocked by the neutron shield when the chemical neutron emitter is unaligned with the aperture. In various embodiments, movement of one or more of the chemical neutron emitter or the neutron shield can be controlled such that the aperture and the chemical neutron emitter operatively align with each other during a selected portion of the movement, generating pulses of neutrons output from the neutron shield. Additional apparatus, systems, and methods are disclosed.

Abstract: Described herein are neutron generators that employ direct field ionization of ionizable fusion gases, as well as well-logging tools and methods that utilize such neutron generators. In various embodiments, the neutron generator includes a cylindrical field-ionization structure distributed around the inner surface of a tubular housing, and a cylindrical ion-accelerating grid disposed about the longitudinal axis concentrically to the field-ionization structure. Ions generated by the field-ionization structure may accumulate inside the ion-accelerating grid, from which they can be axially extracted and accelerated towards a fusion target. Additional tools, systems, and methods are disclosed.

Abstract: A method for cement evaluation may include generating a gamma ray, from a radioactive source, into cement disposed between a casing and a geological formation. Photons reflected from the geological formation and the cement are detected on a gamma detector having a collimator. A detector-to-source distance, a collimator angle, and/or a collimator diameter are set to provide an energy spectra independent of the geological formation. The quality of the cement may be determined based on the energy spectra of the detected photons.

Abstract: A gamma-ray spectrometer calibration system comprises a photomultiplier tube and analysis electronics. The photomultiplier tube provides one or more reference signals that are analyzed relative to a spectrum by the analysis electronics to calibrate a gamma-ray spectrometer. Additional apparatus, methods, and systems are disclosed.

Abstract: A radiation sensor is provided. The sensor includes a rugged scintillator, a photo-sensor, a bundle of one or more optical fibers having a first end connected to the rugged scintillator and a second end connected to the photo sensor, a power supply coupled with the photo-sensor, and a processor electronically coupled with the photo-sensor.

Abstract: A laser photopeak location system comprises a gamma-ray spectrometer and a processor. The processor computes a plurality of correlation coefficients based on a comparison of a pulse-height spectrum of the gamma-ray spectrometer with an array of values. The processor locates one or more photopeaks of the pulse-height spectrum based on at least one of the plurality of correlation coefficients. Additional apparatus, methods, and systems are disclosed.

Abstract: A method, in some embodiments, comprises lowering a neutron wireline tool into a cased borehole containing casing fluid, determining a ratio of inelastic count rate to capture count rate using gammas passing through the casing fluid, and calculating a capture cross section of the casing fluid using the ratio.

Abstract: Various embodiments can include apparatus or methods to operate and provide detection packages. In various embodiments, detection packages may include an illuminating device, a photodetector, and an optical coupling component disposed between the illuminating device and the photodetector, where the optical coupling component can be structured to enhance the coupling of light from the illuminating device to the photodetector. Additional apparatus, systems, and methods are disclosed.

Abstract: Casing condition is an important concern to oilfield operators. Systems and methods are disclosed herein for using neutron logging tools to measure casing condition, using windows in the gamma energy spectrum that are sensitive and insensitive to casing condition to obtain a ratio having a value that ranges between one extreme representative of completely absent casing and an opposite extreme representative of casing in good condition. The sensitive (“divergence”) window may be positioned at or near 7.65 MeV, the characteristic energy of gamma rays from a neutron capture event by an iron nucleus. The insensitive (“consistency”) window is preferably adjacent to the divergence window with a comparable size to the divergence window. A suitable division point between the windows may be about 6.25 MeV.

Abstract: A well logging tool includes a neutron generator to generate and emit energetic neutrons using substantially exclusively a T-T fusion reaction. The well logging tool can include measuring instrumentation for measurement and logging of formation parameters based on elastic scattering in subsurface formations of neutrons emitted by the neutron generator. The neutron generator can have a concentric layout, in which a cylindrical target structure loaded with tritium particles is located co-axially in an elongate cylindrical housing, with mobile tritium ions being accelerated radially inwardly into impact with the target structure. Production of the mobile tritium ions may be by field ionization through operation of a nano-structure field ionization array.

Abstract: In some embodiments, a method and apparatus, as well as an article, may operate to estimate a property of an earth formation by generating at least one shale model to represent an earth formation comprised of a non-zero percentage of shale. The shale model includes two curves to represent a relationship between a porosity parameter and a pulsed neutron measurement at two different corresponding percentages of gas saturation, respectively. A matrix model representing an earth formation with 0% shale is combined with one or more shale models to create a formation model. Measured pulsed neutron data is compared with the formation model to estimate a property of the earth formation. Additional apparatus, systems, and methods are disclosed.

Abstract: A gamma-ray spectrometer calibration system comprises a light guide, a photomultiplier tube, a laser, and analysis electronics. The light guide is optically coupled to the scintillation crystal, the laser and the photomultiplier tube, such that the laser can provide reference signals to the photomultiplier tube. In some embodiments, one or more temperature sensors are provided, such that the analysis electronics determine initial settings and adjust the initial settings based on the temperatures measured by the temperature sensors. Additional apparatus, methods, and systems are disclosed.

Abstract: An accelerator neutron source (ANS) including a field ionization (FI) array configured to generate deuterium and tritium ions and a plasma for containing the deuterium and tritium ions produced by the FI array. The ANS also includes a target comprising deuterium and tritium ions and the ANS is configured to accelerate deuterium and tritium ions produced by the FI array toward the target to generate neutrons by applying a voltage to an accelerating electrode.

Abstract: Various embodiments include apparatus and methods to conduct a triple phase evaluation of a formation. The evaluation can be performed using a pulsed-neutron tool including a long detector and a detector to make sigma measurements. Additional apparatus, systems, and methods are disclosed.