A method for measuring subterranean formation porosity includes the steps of: deploying a nuclear logging tool having one or more neutron sources and two or more dual-function detectors disposed in into a subterranean formation; causing the one or more neutron sources to emit neutrons in a plurality of neutron pulses into the subterranean formation and generating neutrons and gamma rays in the subterranean formation; obtaining one or more neutron count rates for each of the two or more detectors; determining a formation type of the subterranean formation based on gamma rays received at the one or more detectors; calculating one or more neutron count rate ratios between the neutron count rates of two detectors selected from the two or more detectors; and obtaining one or more formation porosities based on the formation type and the one or more neutron count rate ratios.

Methods and tools for determining one or more parameters of an earth formation using time-of-flight (TOF) measurements of fast neutrons through the formation are disclosed. The disclosed tools feature a neutron source capable of emitting a population of fast neutrons having a distribution of neutron energies and one or more neutron detectors. The TOF of the fast neutrons travelling from the neutron source to the detector(s) and traversing a portion of the formation is measured and binned as a function of TOF (which is a function of neutron energy). By determining which neutron energies are attenuated by the intervening formation, the composition of the intervening formation is determined.

Systems and methods may utilize information collected by a pulsed-neutron logging tool along with modeling a characterization of a borehole to form a 3-stage correction algorithm. This algorithm may be used to find an oil, water, and gas holdup in the borehole. During operations, a pulsed neutron logging tool which emits neutrons to interact with nuclei inducing gamma radiation. The gamma radiation is detected into a response which may be correlated to the location of a holdup in a borehole by using the entire spectrum or ratios of selected peaks. In examples, a borehole density index may be implemented to complement the response and improve accuracy and measurement confidence.

Systems and methods for determining holdup in a wellbore using a neutron-based downhole tool. In examples, the tool includes nuclear detectors that may measure gammas induced by highly energized pulsed-neutrons emitted by a generator. The characteristic energy and intensity of detected gammas indicate the elemental concentration for that interaction type. A detector response may be correlated to the borehole holdup by using the entire spectrum or the ratios of selected peaks. As a result, measurements taken by the neutron-based downhole tool may allow for a two component (oil and water) or a three component (oil, water, and gas) measurement. The two component or three component measurements may be further processed using machine learning (ML) and/or artificial intelligence (AI) with additional enhancements of semi-analytical physics algorithms performed at the employed network's nodes (or hidden layers).

A method for wireline or logging-while-drilling systems that uses pulsed neutron sources coupled to multiple dual-function radiation detectors of neutrons and gamma rays, as well as a non-transitory computer readable memory device that can distinguish using pulse shape discrimination techniques the neutrons from the gamma rays in order to measure thermal neutron time-decay signals and thermal neutron capture gamma ray time-decay signals that are later further process using the non-transitory computer readable memory device to obtain a borehole sigma and formation sigma that are not affected by near-wellbore environments.

A method for obtaining nuclear measurement data includes measuring a burst gate source intensity. The method also includes measuring at least one of burst gate neutron count rate or a capture gate neutron count rate at a neutron detector arranged proximate a gamma ray detector. The method further includes determining, based at least in part on the burst gate source intensity and at least one of the burst gate neutron count rate or the capture gate neutron count rate, a normalized neutron count rate. The method also includes determining at least one of an inelastic spectrum or a capture spectrum. The method includes determining based at least in part on the normalized neutron count rate, at least one of a corrected inelastic spectrum or a corrected capture spectrum.

A method and apparatus of logging downhole formation and obtaining formation porosity using a pulsed neutron generator and multiple dual-function detectors that detect both neutrons and gamma rays. Ratios of thermal neutrons, epithermal neutrons, and capture gamma rays from multiple detectors are utilized to obtain neutron porosity, gamma porosity and formation porosity by using a trained neural network. The method can provide formation porosity measurements independent of environmental factors, such as borehole size, tool standoff, salinity, temperature, pressure, etc. Effects from environmental factors can be automatically corrected by employing multiple dual-function detectors that detect both neutrons and gamma rays.

A nuclear logging tool has a housing, one or more neutron sources, one or more shields, and two or more detectors disposed about the housing. Each of the one or more neutron sources is configured to generate neutrons in pulses or continuously and each of the two or more detectors is operable to detect neutrons and gamma rays. The two or more detectors include a first detector disposed at a first distance from a first neutron source and a second detector disposed at a second distance from the first neutron source. The first distance is shorter than the second distance. The first distance and the second distance is measured in the longitudinal direction of the housing. Each shield is operable to absorb neutrons and gamma rays and is disposed inside the housing between one of the one or more neutron source and one of the one or more detectors.

Formation porosity is measured using a logging tool that has a pulsed neutron generator and multiple dual-function detectors that detect both neutrons and gamma rays. Ratios of thermal neutrons, epithermal neutrons, and capture gamma rays from multiple detectors are utilized to obtain multiple neutron porosities and multiple gamma-ray porosities within different depth of investigations. The neutron porosity and the gamma-ray porosity may be further corrected by excluding peak areas attributable to hydrogen and/or chlorine to reduce the shale effect and/or the chlorine effect. The neutron porosity and the gamma-ray porosity may be combined to provide improved porosity evaluations within different depth of investigations into the formation in the entire porosity measurement range (0-100 p.u.).

A method and apparatus of logging downhole formation and obtaining formation porosity using a pulsed neutron generator and multiple dual-function detectors that detect both neutrons and gamma rays. Ratios of thermal neutrons, epithermal neutrons, and capture gamma rays from multiple detectors are utilized to obtain neutron porosity, gamma porosity and formation porosity by using a trained neural network. The method can provide formation porosity measurements independent of environmental factors, such as borehole size, tool standoff, salinity, temperature, pressure, etc. Effects from environmental factors can be automatically corrected by employing multiple dual-function detectors that detect both neutrons and gamma rays.