A first example azimuthal neutron porosity tool for imaging foiniation and cement volumes surrounding a borehole is provided, the tool including at least an internal length comprising a sonde section, wherein said sonde section further comprises one sonde-dependent electronics; a slip-ring and motor section; and a plurality of tool logic electronics and PSUs. An alternative azimuthal neutron porosity tool for imaging formation and cement volumes surrounding a borehole is also provided, the tool including at least a far space detector; a near space detector; and a source located within a moderator shield that rotates around an internal tool axis.

A method for determining a fractional volume of at least one component of a formation includes entering into a computer a number of detected radiation events resulting from imparting neutrons into the formation at an energy level of at least 1 million electron volts (MeV). The detected radiation events correspond to at least one of an energy level of the imparted neutrons and thermal or epithermal energy neutrons. A measurement of at least one additional petrophysical parameter of the formation is made. The at least one additional petrophysical parameter measurement and at least one of a fast neutron cross-section and a thermal neutron cross-section determined from the detected radiation events are used in the computer to determine the fractional volume of the at least one component of the formation. In another embodiment, the fast neutron cross-section and the thermal neutron cross-section may be used on combination to determine the fractional volume.

Embodiments of the present disclosure include a downhole inspection system including a neutron generation unit operable to emit neutrons toward a target in a wellbore. The system also includes a neutron detection unit fixed relative to the neutron generator and operable to detect thermal neutrons from the target. The system includes a shielding arrangement forming at least a portion of the neutron detection unit, the shielding arrangement blocking at least a portion of the thermal neutrons, from penetrating beyond a predetermined radial location within the neutron detection unit.

A method for evaluating induced fractures in a wellbore includes obtaining a first set of data in a wellbore using a downhole logging tool. A first proppant is pumped into the wellbore, after the first set of data is captured. The first proppant includes a first tracer that is not radioactive. A second proppant is also pumped into the wellbore, after the first proppant is pumped into the wellbore. The second proppant includes a second tracer that is not radioactive, and the second tracer is different than the first tracer. A second set of data is obtained in the wellbore using the downhole tool after the first and second proppants are pumped into the wellbore. The first and second sets of data are compared.

A method for determining a fractional volume of at least one component of a formation includes entering into a computer a number of detected radiation events resulting from imparting neutrons into the formation at an energy level of at least 1 million electron volts (MeV). The detected radiation events correspond to at least one of an energy level of the imparted neutrons and thermal or epithermal energy neutrons. A measurement of at least one additional petrophysical parameter of the formation is made. The at least one additional petrophysical parameter measurement and at least one of a fast neutron cross-section and a thermal neutron cross-section determined from the detected radiation events are used in the computer to determine the fractional volume of the at least one component of the formation. In another embodiment, the fast neutron cross-section and the thermal neutron cross-section may be used on combination to determine the fractional volume.

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.

A first example azimuthal neutron porosity tool for imaging formation and cement volumes surrounding a borehole is provided, the tool including at least an internal length comprising a sonde section, wherein said sonde section further comprises one sonde-dependent electronics; a slip-ring and motor section; and a plurality of tool logic electronics and PSUs. An alternative azimuthal neutron porosity tool for imaging formation and cement volumes surrounding a borehole is also provided, the tool including at least a far space detector; a near space detector; and a source located within a moderator shield that rotates around an internal tool axis.

A method for determining formation hydrogen index includes using as input to a computer measurements of numbers of burst gamma rays (gamma rays detected during operation of a pulsed neutron source) and numbers of thermal neutron capture gamma rays made at two different axial spacings from the pulsed neutron source. A ratio of the numbers of burst gamma rays and a ratio of the numbers of thermal neutron capture gamma rays is determined. A corrected ratio of the numbers of thermal neutron capture gamma rays using the ratio of numbers of burst gamma rays is determined. The formation hydrogen index is determined from the corrected ratio.

A system that may identify when a pulsed neutron generator is operating while disposed in an undesirable environment, such as in air, may include a pulsed neutron generator designed to emit neutrons in an environment. The system may also include a radiation detector designed to take measurements of the neutrons. The system may also include data processing circuitry designed to determine if the environment surrounding the pulsed neutron generator is air based at least in part on a neutron signal obtained by the radiation detector. The determination may include comparing one or more characteristics of the neutron signal with corresponding reference characteristics.

A method for evaluating induced fractures in a wellbore includes obtaining a first set of data in a wellbore using a downhole logging tool. A first proppant is pumped into the wellbore, after the first set of data is captured. The first proppant includes a first tracer that is not radioactive. A second proppant is also pumped into the wellbore, after the first proppant is pumped into the wellbore. The second proppant includes a second tracer that is not radioactive, and the second tracer is different than the first tracer. A second set of data is obtained in the wellbore using the downhole tool after the first and second proppants are pumped into the wellbore. The first and second sets of data are compared.