Methods and related systems are described for gamma-ray detection. A gamma-ray detector is made depending on its properties and how those properties are affected by the data analysis. Desirable properties for a downhole detector include; high temperature operation, reliable/robust packaging, good resolution, high countrate capability, high density, high Z, low radioactive background, low neutron cross-section, high light output, single decay time, efficiency, linearity, size availability, etc. Since no single detector has the optimum of all these properties, a downhole tool design preferably picks the best combination of these in existing detectors, which will optimize the performance of the measurement in the required environment and live with the remaining non-optimum properties. A preferable detector choice is one where the required measurement precision (logging speed) is obtained for all of the required inelastic elements and/or minimization of unwanted background signals that complicate the data analysis.

Methods, systems, and devices for evaluating an earth formation intersected by a borehole. Methods may include irradiating the earth formation using a radiation source to provoke radiation from the formation responsive to the irradiation; taking a radiation measurement and thereby generating radiation measurement information by producing light scintillations from a scintillation material responsive to the absorption by the scintillation material of the radiation from the formation and substantial intrinsic radiation of the scintillation material; and estimating a parameter of interest of the earth formation using the radiation measurement information.

Systems and methods of the present disclosure relate to determining a borehole holdup. A method comprises logging a well with a pulsed-neutron logging (PNL) tool; receiving, via the PNL tool, transient decay measurements, capture spectrum measurements, and inelastic spectrum measurements; extracting information from each of the capture spectrum measurements, the inelastic spectrum measurements, and the transient decay measurements; inputting all of the extracted information as a single input into artificial neural networks; and determining the borehole holdup with the artificial neural networks.

A method for analyzing a formation includes entering into a computer a number of detected gamma rays resulting from imparting neutrons into the formation. The detected gamma rays are characterized by energy levels thereof. A number of detected gamma rays in each energy level comprises a measured spectrum. In the computer, a non-Gaussian filter is applied to a reference spectrum to match the measured spectrum in shape. The filtered reference spectrum and measured spectrum are used to determine a fractional volume of at least one component of the formation.

Methods and related systems are described for gamma-ray detection. A gamma-ray detector is made depending on its properties and how those properties are affected by the data analysis. Desirable properties for a downhole detector include; high temperature operation, reliable/robust packaging, good resolution, high countrate capability, high density, high Z, low radioactive background, low neutron cross-section, high light output, single decay time, efficiency, linearity, size availability, etc. Since no single detector has the optimum of all these properties, a downhole tool design preferably picks the best combination of these in existing detectors, which will optimize the performance of the measurement in the required environment and live with the remaining non-optimum properties. A preferable detector choice is one where the required measurement precision (logging speed) is obtained for all of the required inelastic elements and/or minimization of unwanted background signals that complicate the data analysis.

An apparatus for estimating a property of an earth formation and a borehole fluid includes a carrier configured to be disposed in a borehole, and a pulsed neutron measurement assembly including a pulsed neutron source configured to emit neutrons into the borehole and the earth formation, and a gamma ray detector. The apparatus also includes a fluid density measurement assembly including the gamma ray detector and a gamma ray source configured to irradiate a borehole fluid with gamma rays. The gamma ray detector is positioned relative to the gamma ray source to detect both of: gamma rays resulting from neutron interactions and gamma rays emitted from the borehole fluid in response to irradiation from the gamma ray source. The apparatus further includes a processor configured to differentiate a pulsed neutron gamma ray spectrum associated with the interactions from a density gamma ray spectrum.

A system may include one or more downhole tools, where a first downhole tool includes a pulsed neutron generator to emit neutrons into a borehole of a geological formation and one or more gamma-ray detectors to obtain a measurement of gamma-ray emissions, of a borehole environment, induced by the emitted neutrons. The system may also include data processing circuitry to determine a Sigma value associated with the borehole environment based on the measurement and determine elemental concentrations, excluding lithium, based on one or more gamma-ray energy spectra obtained via the one or more downhole tools. The data processing circuitry may also determine an elemental Sigma contribution of the elements other than lithium based on the elemental concentrations, determine a lithium Sigma contribution based on a difference between the Sigma value and the elemental Sigma contribution, and determine a lithium concentration within the borehole environment based on the lithium Sigma contribution.

A method for evaluating a formation includes determining a number of detected gamma rays resulting from imparting neutrons into a formation. The detected gamma rays are each characterized by an energy level thereof The gamma rays are detected at a first distance from a position of imparting the neutrons into the formation. Those of the detected gamma rays attributable to neutron capture by hydrogen nuclei are removed from the number of detected gamma rays. The number of detected gamma rays having hydrogen neutron capture gamma rays removed therefrom are used to calculate a property of the formation.

A method and system for identifying formation porosity and formation lithology. The method may include disposing a PNL tool into a borehole that is disposed in a formation, emitting a neutron from a neutron source on the PNL tool into the formation, and capturing one or more gammas expelled from formation in response to the neutron from the neutron source to form a plurality of pulsed neutron logging (PNL) measurements in a log. The method may further include identifying a formation porosity and a formation lithology with an artificial neural network that at least partially incorporates the PNL measurements.

A system may include one or more downhole tools, where a first downhole tool includes a pulsed neutron generator to emit neutrons into a borehole of a geological formation and one or more gamma-ray detectors to obtain a measurement of gamma-ray emissions, of a borehole environment, induced by the emitted neutrons. The system may also include data processing circuitry to determine a Sigma value associated with the borehole environment based on the measurement and determine elemental concentrations, excluding lithium, based on one or more gamma-ray energy spectra obtained via the one or more downhole tools. The data processing circuitry may also determine an elemental Sigma contribution of the elements other than lithium based on the elemental concentrations, determine a lithium Sigma contribution based on a difference between the Sigma value and the elemental Sigma contribution, and determine a lithium concentration within the borehole environment based on the lithium Sigma contribution.