A computer-implemented method that uses a preprogrammed neural network and a trained neural network computer program product to predict and then compared borehole and formation sigmas, when using a pulse neutron source and at least three dual-function radiation detectors. These dual-function radiation detectors are used for detecting both neutrons and gamma rays and further pre-programmed to distinguish between neutrons and gamma rays by using pulse shape discrimination techniques. The trained neural network computer program product can be used on above-surface systems, as well as below surface systems like borehole assemblies in logging-while-drilling systems. Once thermal neutron time-decay signals and capture gamma ray time-decay signals are measured by the at least three-dual function radiation detectors, a non-transitory computer readable memory device with the trained neural network computer program product is used to obtain a true borehole sigma and true formation sigma as the measurements are not affected by near-wellbore environments.

A method for measuring an oil saturation value of a subterrain formation uses a tool having multiple dual-function detectors that detect neutrons and gamma rays. The method includes emitting neutrons into the formation, detecting neutrons and gamma ray signals form the formation using the detectors, determining formation parameters including the formation type and formation porosity, and further determining parameters such as C/O ratios at each of the detectors, a total neutron count rate at each of detectors, a fast neutron count rate at each of detectors, and a thermal neutron count rate at each of the three or more detector, and calculating the oil saturation value using the determined parameters.

A computer-implemented method that uses a preprogrammed neural network and a trained neural network computer program product to predict and then compared borehole and formation sigmas, when using a pulse neutron source and at least three dual-function radiation detectors. These dual-function radiation detectors are used for detecting both neutrons and gamma rays and further pre-programmed to distinguish between neutrons and gamma rays by using pulse shape discrimination techniques. The trained neural network computer program product can be used on above-surface systems, as well as below surface systems like borehole assemblies in logging-while-drilling systems. Once thermal neutron time-decay signals and capture gamma ray time-decay signals are measured by the at least three-dual function radiation detectors, a non-transitory computer readable memory device with the trained neural network computer program product is used to obtain a true borehole sigma and true formation sigma as the measurements are not affected by near-wellbore environments.

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 a gas saturation value of a subterrain formation involves a tool having multiple dual-function detectors that detect neutrons and gamma rays. The method includes steps of emitting neutrons into the formation, detecting neutrons and gamma ray signals form the formation using the detectors, determining formation parameters including the formation type and formation porosity, and further determining parameters such as the ratio of thermal neutron count rates from at least two of three detectors, the ratio of capture gamma count rates from at least two of three detectors, and calculating the real-time gas saturation value using the determined parameters.

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 determining a corrected neutron gamma density of a formation includes emitting neutrons into a formation using a neutron source to generate gamma-rays. Additionally, the method includes detecting a first count rate of gamma-rays and a gamma-ray spectrum using at least a gamma-ray detector of the downhole tool. The method also includes detecting a second count rate of neutrons using a neutron detector. The method includes using a processor to perform a gamma-ray spectroscopy analysis on the formation based on the gamma-ray spectrum and determining a correction based on results of the gamma-ray spectroscopy analysis. The method includes applying the correction to the first count rate or the second count rate and determining a neutron gamma density of the formation based on a first corrected count rate of gamma-rays or a second corrected count rate of neutrons. The method also includes outputting the determined density of the formation.

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.

Methods of using capture gamma-ray spectroscopy for analyzing gravel-packs, frac-packs, and cement are disclosed herein. The methods can include distinguishing particles placed in a borehole region from particles placed in a subterranean formation outside of the borehole region, by utilizing a slurry comprising a liquid, particles, and a thermal neutron absorbing material to place the particles into the borehole region. The methods can also include obtaining first and second data sets by lowering into a borehole traversing the borehole region a pulsed neutron logging tool comprising a pulsed neutron source and a detector, emitting pulses of neutrons from the pulsed neutron source into the borehole region at intervals of one pulse per about 1,000 μsec for the first data set and about one pulse per about 100 μsec for the second data set, and detecting capture gamma rays resulting from nuclear reactions in the borehole and the subterranean formation.

A method for determining a formation thermal neutron decay rate from measurements of radiation resulting from at least one burst of high energy neutrons into formations surrounding a wellbore includes determining a first apparent neutron decay rate in a time window beginning at a first selected time after an end of the at least one burst, a second apparent decay rate from a time window beginning at a second selected time after the burst and a third apparent decay rate from a third selected time after the burst. The second time is later than the first time. A thermal neutron capture cross section of fluid in the wellbore is determined. A decay rate correction factor is determined based on the first and second apparent decay rates and a parameter indicative of the wellbore capture cross-section. The correction factor is applied to the third apparent decay rate to determine the formation thermal neutron decay rate.