The present disclosure provides methods for identifying chemical diverter material placed in a borehole region and provides chemical diverter material. In one embodiment, a method for detecting diverter material placed in a borehole region includes (a) obtaining a first data set by: emitting pulses of neutrons from the pulsed neutron source into the borehole region and detecting capture gamma rays resulting from nuclear reactions in the borehole region; (b) placing a diverter material comprising aqueous-swellable particles and a thermal neutron absorbing material into the borehole region; (c) obtaining a second data set by: emitting pulses of neutrons from the first pulsed neutron source or a second pulsed neutron source into the borehole region, and detecting capture gamma rays in the borehole; and (d) comparing the first data set and the second data set to determine the location of diverter material placed in the borehole region.

A method for determining a petrophysical property of a formation includes detecting gamma rays at two different spaced apart positions from a position of emitting neutrons into the formation at an energy level sufficient to induce inelastic scatting gamma rays. The neutrons are emitted in a plurality of bursts of neutrons into the formation, the bursts each having a first selected duration. Each burst is followed by a wait time having a second selected duration, the gamma rays detected during each of the bursts and each of the wait times. A ratio of numbers of gamma rays detected during the bursts is determined (burst ratio). A ratio of numbers of gamma rays detected during the wait times is determined (capture ratio). The burst ratio is used to correct the capture ratio. The petrophysical property is determined from the corrected capture ratio.

A method for determining hydrogen index includes using measurements of gamma rays detected during operation of a pulsed neutron source and numbers of thermal neutron capture gamma rays made at at least two different axial spacings from a pulsed neutron source. Either a first ratio of or a first logarithm of the first ratio of the burst gamma rays is determined for a first and second axial distance from the neutron source. A second logarithm is determined of a second ratio of the thermal neutron capture gamma rays detected at a first axial spacing with respect to the numbers detected at a second axial spacing. A corrected second ratio of the numbers of thermal neutron capture gamma rays is determined using either (i) the first logarithm and (ii) the first ratio, and the second logarithm. The corrected second ratio is used to determine the hydrogen index.

A method to interpret and quantify mineral compositions and concentrations, the method including: determining, with a computer, mineral composition models from a non-linear inversion of core or log elemental and mineral concentration data; and determining, with a computer, mineral concentrations for subsurface region from a linear inversion of core or geochemical log data from the subsurface region or analogous region and the mineral composition models.

The techniques as described herein enhance the accuracy and precision of mineralogy analysis in elemental spectroscopy logging by utilizing oxide standards and/or rock-forming mineral compounds as reference materials that provide more representative and realistic signatures of geological formations. A method comprises logging a wellbore with a tool and fitting reference spectra from oxide compounds and/or rock-forming mineral compounds against measured gamma spectra obtained with the tool, to characterize a subterranean formation that the wellbore extends through.

Disclosed are apparatus, systems, and methods for determining the completeness of the cement sheath or gravel-pack annulus of a borehole based on gamma counts or count rates measured with a pulsed neuron tool deployed in the borehole in conjunction with a quantitative relationship between certain gamma count (rate) ratios and a parameter of completeness. In various embodiments, the determination utilizes the ratio of the net long inelastic count (rate) and the near capture count (rate), or the ratio of the net near inelastic count (rate) and the long capture count (rate). Additional apparatus, systems, and methods are disclosed.

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.

A method and system for identifying one or more petrophysical properties in a formation. The method and system may include disposing a pulsed-neutron logging tool into a borehole that is disposed in a formation, emitting a neutron from a neutron source on the pulsed-neutron logging 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 and system may further include comparing the log to a database with a cost function to form a solution; and identifying a plurality of petrophysical properties based at least in part on the solution.

A method and apparatus for characterizing the properties of the region surrounding a borehole. In one embodiment, a downhole tool including a neutron generator is used to generate neutron pulses into the region surrounding the borehole. At least two detectors in the downhole tool detect gamma radiation pulses resulting from the capture of neutrons by elements in the surrounding region. For each gamma radiation pulse detected, a record is made of its amplitude and the time that the pulse was detected, measured to a resolution of a few microseconds. The amplitude/timestamp data is stored in memory in the tool for later retrieval. The data generated is stored in memory and interpretation can be made by the operator or log analyst after the memory module data has been transferred from the tool.

The present disclosure describes various embodiments related to methods for determining salinity of water in a borehole of a formation and the water in the formation. Various methods may use inelastic and capture gamma-ray spectra obtained from a pulsed neutron logging tool. Various embodiments may use a ratio of chlorine from a capture spectrum to oxygen from an inelastic spectrum for a near and a far detector to calculate apparent salinity ratios for water in a borehole and a formation. From the apparent salinity ratios, a borehole salinity and a formation salinity may be calculated using a tool characterization database and without using formation water saturation for the calculation. Other embodiments may be disclosed or claimed.