A distance of a water flow path and a velocity of the water flow is calculated using data obtained from both a pulsed neutron sensor and distributed acoustic sensors. The two distance and velocity values are compared to obtain a first calculated distance and velocity. The distance of the water flow path and the velocity of the water flow are calculated using the Doppler data obtained from distributed Doppler sensors. The distance and velocity values are compared with the first calculated distance and first calculated velocity to obtain a second calculated distance and velocity values. The distance of the water flow path and the velocity of the water flow are calculated using temperature data obtained from distributed temperature sensors. The distance and velocity values are compared with the second calculated distance and velocity to determine a distance of a cement interface, and a velocity of a water flow therein.

In some embodiments, a method and apparatus, as well as an article, may operate to estimate a property of an earth formation by generating at least one shale model to represent an earth formation comprised of a non-zero percentage of shale. The shale model includes two curves to represent a relationship between a porosity parameter and a pulsed neutron measurement at two different corresponding percentages of gas saturation, respectively. A matrix model representing an earth formation with 0% shale is combined with one or more shale models to create a formation model. Measured pulsed neutron data is compared with the formation model to estimate a property of the earth formation. 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.

Methods and systems for determining the elemental composition of formation rock are disclosed. The systems include a pulsed-neutron geochemical logging tool that is conveyed in a borehole traversing the formation. The pulsed-neutron geochemical logging tool can collect inelastic and capture neutron spectra. The inelastic and capture spectra are processed to provide the elemental composition of formation rock after removing contributions due to elements in the borehole and in the pores of the formation.

A method for determining a composition of a formation, includes characterizing by energy detected gamma rays resulting from interaction of neutrons that irradiated the formation. Elemental yields are determined by spectrally analyzing the energy characterized gamma rays. A subset of the elemental yields is selected as background yields. The background yields are filtered. An apparent contribution of the filtered background yields to the characterized gamma rays is determined. Foreground elemental yields are determined by spectrally analyzing the characterized gamma rays having the apparent contribution removed.

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.

Systems, methods, and devices for evaluating an earth formation intersected by a borehole. Apparatus may include at least one radiation detector configured to generate an analog electrical signal responsive to a plurality of radiation events, comprising absorption of incident ionizing radiation at a corresponding energy level, and an ionizing radiation spectrometer configured to convert each analog electrical signal from the at least one radiation detector into a plurality of digital signal pulses corresponding to the radiation events and resolve the plurality of digital signal pulses into radiation count information representative of the radiation events. Spectrometers include an input channel for each detector of the at least one radiation detector comprising an analog-to-digital converter (ADC) and configured to convert the analog electrical signal for each detector into the plurality of digital signal pulses; and at least one processor configured to generate the radiation count information.

Various embodiments include apparatus and methods to conduct a triple phase evaluation of a formation. The evaluation can be performed using a pulsed-neutron tool including a long detector and a detector to make sigma measurements. Additional apparatus, systems, and methods are disclosed.

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.

A presence of cement may be identified based on a downhole tool that may emit neutrons into a wellbore having at least one cement casing. The neutrons may interact with the particular material via inelastic scattering, inelastic neutron reactions, capture of neutrons and/or neutron activation through one of these reactions and cause a material to emit an energy spectrum of gamma rays, and wherein the downhole tool is configured to detect an energy spectrum of the gamma rays that is specific to at least one of a plurality of elements and associated a region within the wellbore. An amount of elements, such as calcium and silicon, may be determined from the gamma ray spectra that may indicate a present of cement within the wellbore.