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.

A gamma ray spectrum unfolding method for elemental capture spectroscopy logging and a device therefor including the steps of first preprocessing the data obtained from an elemental capture spectrometry instrument; constructing a primary element group and an auxiliary element group according to the degree of interactions among the elements via theoretical analysis and numerical calculation of spectrum profiles, characteristic peak channels, and backgrounds of different elements; unfolding by using the least square method based on the construction of the primary element group and the auxiliary element group; and finally reconstructing the spectrum based on theory according to the yield of each element obtained by unfolding with the least square method, and comparing the measured gamma ray spectrum with the reconstructed gamma ray spectrum for error control, thereby improving the spectrum unfolding precision.

The inelastic and capture ratio is optimized for porosity measurements in downhole applications. Pulsed-neutron data is acquired using a pulsed-neutron downhole tool. At each sampling point or log depth, the inelastic count rates and capture rates are computed. The inelastic count rate is corrected for the capture count background to increase porosity sensitivity. The capture count rate is computed by summing a range of time windows in the decay curve. In this process, the inelastic and capture responses are matched for borehole sensitivity. The ratio of inelastic and capture counts is computed. This ratio is the input to the characterized transform algorithm to compute measured porosity.

A neutron imaging device employs a neutron source including a sealed enclosure, gamma ray detector(s) spaced from the neutron source, and particle detector(s) disposed in the sealed enclosure of the neutron source. The output of the particle detector(s) can be used to obtain a direction of particles generated by the neutron source and corresponding directions of neutrons generated by the neutron source. Such information can be processed to determine locations in the surrounding borehole environment where the secondary gamma rays are generated and determine data representing formation density at such locations. In one aspect, the gamma ray detector(s) of the neutron imaging device can include at least one scintillation crystal with shielding disposed proximate opposite ends of the scintillation crystal. In another aspect, the particle detector(s) of the neutron imaging device can include a resistive anode encoder having a ceramic substrate and resistive glaze.

Through-tubing, cased-hole sealed material density can be evaluated using gamma ray measurements. Density evaluation comprises detecting, by at least one detector positioned within a casing of a wellbore including a sealing material positioned between the casing and a subsurface formation, electromagnetic radiation generated in response to nuclear radiation being emitted outward toward the subsurface formation, determining an electromagnetic radiation count based on the detected electromagnetic radiation, selecting at least one of a first reference material having a density that is less than a density of the sealing material and a second reference material having a density that is greater than the density of the sealing material, adjusting the electromagnetic radiation count based on the density of the at least one of the first reference material and the second reference material, and determining a density of the sealing material based on the adjusted electromagnetic radiation count.

A method for making natural gamma ray measurements of a subterranean formation includes causing a natural gamma ray sensor on an LWD tool to acquire a spectral gamma ray measurement while a neutron source emits neutrons. The measurements are evaluated to compute first and second drilling fluid activation corrections using corresponding first and second correction methodologies. The first and second corrections are processed to compute a third drilling fluid activation correction which is applied to the gamma ray measurements to compute a corrected total natural gamma ray measurement.

Methods and associated systems are disclosed for performing a logging operation within a subterranean wellbore extending within a subterranean reservoir. In an embodiment, the method includes (a) emitting neutrons into the subterranean wellbore or the subterranean reservoir, and (b) detecting gamma rays emitted from atoms disposed within the subterranean wellbore or the subterranean reservoir. In addition, the method includes (c) determining a first gamma ray count within a first energy window of the gamma rays detected at (b), and (d) determining a second gamma ray count within a second energy window of the gamma rays detected at (b). The second energy window is different than the first energy window. Further, the method includes (e) calculating a ratio of the first gamma ray count to the second gamma ray count.

A method and system for determining a density. The method may comprise disposing a nuclear density tool into a wellbore, performing a spectral deconvolution, determining an energy channel for a first measurement layer, recording a count rate with the gamma detector for the first measurement layer, applying a slope operator to the count rate, and identifying a first density of the first measurement layer. The system may comprise a nuclear density tool that includes a gamma source and a gamma detector configured to record a count rate, wherein the gamma detector and the gamma source are disposed on a longitudinal axis of the nuclear density tool. The system may also comprise an information handling system.

A method, including emitting from a source of ultrafast neutrons within a logging tool deployed in a borehole, a pulse of ultrafast neutrons into an irradiated portion of a formation surrounding the borehole. The method further includes detecting, with one or more gamma ray detectors located at increasing distances from the source of ultrafast neutrons, a flux of stimulated gamma rays generated within the irradiated portion of the formation by the pulse of ultrafast neutrons; and determining, from the detected flux of stimulated gamma rays, one or more petrophysical properties of the irradiated portion of the formation.

A method and system for determining a density. The method may comprise disposing a nuclear density tool into a wellbore, performing a spectral deconvolution, determining an energy channel for a first measurement layer, recording a count rate with the gamma detector for the first measurement layer, applying a slope operator to the count rate, and identifying a first density of the first measurement layer. The system may comprise a nuclear density tool that includes a gamma source and a gamma detector configured to record a count rate, wherein the gamma detector and the gamma source are disposed on a longitudinal axis of the nuclear density tool. The system may also comprise an information handling system.