Abstract: The disclosure provides methods of measuring an intrinsic CO ratio in a geological formation by disposing, proximate the formation, a petrophysical tool including at least one gamma-ray detector, reading a carbon gamma-ray peak for the geological formation and an oxygen gamma-ray peak for the geological formation, determining a measured CO ratio of the geological formation from the carbon gamma-ray peak and the oxygen gamma-ray peak, and correcting the measured CO ratio by applying a corrective algorithm specific for the petrophysical tool or the type of petrophysical tool to obtain an intrinsic CO ratio of the geological formation. The corrective algorithm is derived by a mathematical analysis of measured CO ratios of a sample with a known intrinsic CO ratio using the same petrophysical tool or a petrophysical tool representative of a same type of petrophysical tool. Additional methods and systems using this method are provided.

Abstract: A system includes a neutron source positionable within a wellbore to emit one or more neutrons toward a formation surrounding the wellbore. The system also includes a gamma ray detector positionable within the wellbore to detect gamma rays. Further, the system includes a gamma ray analyzer that can perform operations. The operations can include receiving data indicating detected gamma rays from the gamma ray detector. Additionally, the operations include determining, from the data indicating the detected gamma rays, an amount of activated tracer material present within the wellbore originating from non-radioactive tracer material of drill-in fluid. The operations also include determining, from the amount of activated tracer material, an amount of filtercake buildup in a wellbore, a depth of fluid-loss filtrate into the formation surrounding the wellbore, or a combination thereof.

Abstract: A system and method for evaluating integrity of cement in a wellbore with multiple casing strings. The system and method may include at least one source that can emit a field of photons, and at least one photon detector spaced away from the source by a first distance that configures the tool to measure cement integrity in a first annulus, by a portion of the source photons being scattered back to the first detector which can produce photon count rates based on energy levels of received photons. Integrity of cement in the first annulus can be determined by the photon count rates. A second detector spaced a second distance from the source can be included and can measure cement integrity in a second annulus that is radially outside the first annulus by producing photon count rates for photons received from the second annulus.

Abstract: Various apparatus or methods are arranged to operate a tool downhole in a well, where the tool has a detection package operable to detect gamma rays. Deviation of energy spectra of detected gamma rays in each selected energy window of a set of selected energy windows with respect to reference energy spectra of the respective selected energy window can be detected. One or more properties of one or more regions around the tool can be determined from the deviations, the regions being between the tool and a source of the detected gamma rays in a formation around the well. Additional apparatus, systems, and methods having a gamma ray detection package can operate in a variety of applications.

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: Methods and systems including establishing a wellbore heterogeneity profiling factor (HPF), establishing a cement quality curve representing a volumetric void space of a completion profile, and comparing the wellbore HPF and the cement quality curve, thereby determining a cement volumetric void space in a wellbore at a target depth having the completion profile.

Abstract: A system and method for evaluating integrity of cement in a wellbore with multiple casing strings. The system and method may include at least one source that can emit a field of photons, and at least one photon detector spaced away from the source by a first distance that configures the tool to measure cement integrity in a first annulus, by a portion of the source photons being scattered back to the first detector which can produce photon count rates based on energy levels of received photons. Integrity of cement in the first annulus can be determined by the photon count rates. A second detector spaced a second distance from the source can be included and can measure cement integrity in a second annulus that is radially outside the first annulus by producing photon count rates for photons received from the second annulus.

Abstract: The disclosure provides methods of measuring an intrinsic CO ratio in a geological formation by disposing, proximate the formation, a petrophysical tool including at least one gamma-ray detector, reading a carbon gamma-ray peak for the geological formation and an oxygen gamma-ray peak for the geological formation, determining a measured CO ratio of the geological formation from the carbon gamma-ray peak and the oxygen gamma-ray peak, and correcting the measured CO ratio by applying a corrective algorithm specific for the petrophysical tool or the type of petrophysical tool to obtain an intrinsic CO ratio of the geological formation. The corrective algorithm is derived by a mathematical analysis of measured CO ratios of a sample with a known intrinsic CO ratio using the same petrophysical tool or a petrophysical tool representative of a same type of petrophysical tool. Additional methods and systems using this method are provided.

Abstract: A method for material evaluation may include detecting photons from gamma ray interactions with material in an annular region between a geological formation and a casing. An energy spectrum is generated from the detected photons. A difference between materials may then be detected based on a comparison of the generated energy spectrum with a reference spectrum for a known material (e.g., good cement, known fluid).

Abstract: The disclosed embodiments include downhole neutron generators and methods to utilize downhole neutron generators in a downhole environment. In one embodiment, a downhole neutron generator includes a heating element to dissipate heat to a first transition metal, which heats up the first transition metal and facilitates the first transition metal to absorb deuterium and tritium gases flowing proximate said transition metal. The downhole neutron generator also includes a second transition metal separated from the target foil, where the second transition metal is doped with of deuterium and the tritium ions, and a laser to direct optical pulses onto a surface of the first transition metal to produce deuterium and the tritium ions from the absorbed deuterium and tritium, where said ions traverse through a back surface of the first transition metal to the second transition metal to interact with the doped deuterium and the tritium ions to initiate fusion reaction.

Abstract: The disclosure provides a well integrity monitoring tool for a wellbore, a method, using a nuclear tool and an EM tool, for well integrity monitoring of a wellbore having a multi-pipe configuration, and a well integrity monitoring system. In one example, the method includes: operating a nuclear tool in the wellbore to make a nuclear measurement at a depth of the wellbore, operating an EM tool in the wellbore to make an EM measurement at the depth of the wellbore, determining a plurality of piping properties of the multi-pipe configuration at the depth employing the EM measurement, determining, employing the piping properties, a processed nuclear measurement from the nuclear measurement, and employing the processed nuclear measurement to determine an integrity of a well material at the depth and within an annulus defined by the multi-pipe configuration.

Abstract: A method may comprise providing a wellbore penetrating a subterranean formation, the wellbore being lined with a pipe and having a cement between the pipe and the wellbore, wherein the cement contains a defect; providing a control spectrum of gamma radiation count rates as a function of energy for a control, wherein the control comprises the cement without the defect; emitting gamma rays into the pipe and the cement having the defect from a source of a nuclear tool disposed in the wellbore; detecting count rates of gamma radiation scattered back from the pipe and the cement having the defect with a detector of the nuclear tool as a function of energy to produce a sample spectrum; and deriving one or more physical attributes related to the defect based on a comparison of the sample spectrum and the control spectrum.

Abstract: Methods including taking a gamma spectrum from a wellbore at a target depth, wherein the wellbore penetrates a subterranean formation and has a completion profile comprising a pipe and an annulus between the pipe and the subterranean formation; determining a cement volumetric void space in the wellbore at the target depth; establishing a cement-void-spatial calibration curve based on obtained gamma spectra representing cement spatial void space locations in the annulus of the completion profile, wherein each cement volumetric void space amount in the wellbore has a characteristic cement-void-spatial calibration curve; comparing the wellbore gamma spectrum and the cement-void-spatial calibration curve; and determining a location of the cement volumetric void space in the wellbore at the target depth.

Abstract: A method for monitoring tubing wall thickness includes conveying a tool through a tubular string in a borehole, the tool including a photon source that directs a photon beam along a radial path toward a wall of the borehole, the tool further including an array of collimated detectors that measure Compton backscattering rates at respective distance bins along the radial path. The method further includes calculating a sequence of ratios between measurements from neighboring detectors. The method further includes identifying one or more local extrema in the sequence, each extremum representing a boundary between different materials. The method further includes determining a wall thickness of the tubular string from absolute or relative positions of the one or more extrema. The method further includes displaying a representation of the wall thickness.

Abstract: A neutron generator includes a gas control interface and a vacuum chamber coupled to the gas control interface. The neutron generator also includes a target rod disposed within the vacuum chamber and having a longitudinal axis aligned with a central axis of the vacuum chamber, and further including a target disposed on a surface of the target rod facing the getter. The neutron generator also includes a planar ion source adjacent to the gas control interface and disposed between the target and the gas control interface. The planar ion source includes an array grid that is offset from the target and generally perpendicular to the longitudinal axis of the target rod.

Abstract: A fiber optic distributed sensing system for installation within a wellbore is provided. The system includes a first set of downhole sensors having one or more nuclear sensors with nuclear field sensitivity. The system additionally includes, a second set of downhole sensors having one or more ElectroMagnetic (EM) sensors with electromagnetic field sensitivity. The fiber optic distributed sensing system also includes a processor system configured to receive data measurements from the first and second sets of sensors and configured to conjointly process the data measurements into representations of physical attributes of the wellbore.

Abstract: Various embodiments include apparatus and methods to conduct neutron-neutron measurements and to evaluate quality of cement between a casing and a formation. A tool can include a neutron source, a far detector, and a near detector, where the far detector and the near detector detect neutrons in response to activation of the neutron source. Measured counts of the detected neutrons can be compared with respect to expected counts of neutrons. From one or more comparisons, the quality of the cement can be evaluated. Additional apparatus, systems, and methods are disclosed.

Abstract: A system and method to determine a characteristic of a wellbore based on count rates of scattered photons. The system and method can include determining at least one characteristic of a material surrounding a wellbore by, emitting photons from a photon source at a location in the wellbore, detecting, via one or more detectors, photons scattered by the material, counting the scattered photons based on an energy level, producing count rates of the detected photons for various energy ranges, and calculating a value of the characteristic based on the count rates. The material can be at least one of mud, mud cake, and earth formation.

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: 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.