Abstract: Systems and methods for drilling a wellbore. The method includes measuring a first distance that a drilling device is raised while connected to a drill string, determining a weight-on-bit in the drill string, determining a second distance to lower the drilling device such that a drill bit at a lower extremity of the drill string approaches toward a bottom of the wellbore, based on the first distance and the weight-on-bit, and lowering the drilling device by the second distance.

Abstract: A method of logging a wellbore casing and an adjacent formation comprises moving a measurement tool inside a borehole of the casing, wherein the casing is filled with air. Concurrently with moving the measurement tool inside the borehole, the method comprises emitting radioactive energy at an initial energy level from a radiation source of the measurement tool, wherein the radioactive energy is directed toward a wall of the casing and along a travel path from the radiation source to one or more detectors of the measurement tool, measuring energy loss of the radioactive energy at the one or more detectors relative to the initial energy level, and detecting a cement property outside of the casing based on the measured energy loss.

Abstract: A method and apparatus is provided to perform dead-time correction in a positron emission tomography (PET) by estimating a full singles spectrum using a scatter model. The scatter model can use a Monte Carlo method, a radiation transfer equation method, an artificial neural network, or an analytical expression. The scatter model simulates scatter based on an emission image/map and an attenuation image/map to estimate Compton scattering. In the full singles spectrum, the singles counts with energies less than 511 keV are determined from the simulated scatter. The attenuation image can be generated based on X-ray computed tomography or based on applying a joint-estimation to PET data.

Abstract: Methods are provided for determining the location and height of cement in a subterranean borehole region using pulsed neutron capture (PNC) logging tools. The methods include obtaining a pre-cementing data set, placing in the borehole region a cement slurry that includes a liquid a thermal neutron absorbing material, obtaining a post-cementing data set, comparing the pre-cementing data set and the post-cementing data set to determine the location of the cement, and correlating the location of the cement to a depth measurement of the borehole to determine the location and height of the cement placed in the borehole region.

Abstract: A method for determining azimuthal formation information using neutron activation, wherein the formation is activated by a neutron source and the activation signal is measured by at least one detector trailing the neutron source during the logging operation. The number of detected gamma rays as a function of the detector azimuth may be used to provide azimuthal information for determining an image of the formation surrounding the borehole.

Abstract: Systems, methods, and devices for inelastic gamma-ray logging are provided. In one embodiment, such a method includes emitting neutrons into a subterranean formation from a downhole tool to produce inelastic gamma-rays, detecting a portion of the inelastic gamma-rays that scatter back to the downhole tool to obtain an inelastic gamma-ray signal, and determining a property of the subterranean formation based at least in part on the inelastic gamma-ray signal. The inelastic gamma-ray signal may be substantially free of epithermal and thermal neutron capture background.

Abstract: Estimating a correction factor from logs of compensated thermal neutron porosity measurements, including modeling each measurement of the compensated thermal neutron porosity measurements of the log as resulting from at least: i) a first contribution correlated to an absorbance of a first portion of neutrons produced by irradiation of the volume attributable to interactions in the volume indicative of pore space in the matrix, and ii) a second contribution correlated to an absorbance of a second portion of the neutrons attributable to trace elements of at least one dominant neutron absorber in the formation; iii) a third contribution correlated to an absorbance of a third portion of the neutrons attributable to dry minerals in the matrix other than dominant neutron absorbers; and estimating the second contribution and determining the correction factor from the second contribution; and correcting a compensated thermal neutron porosity measurement using the correction factor.

Abstract: A formation monitoring system includes a casing that defines an annular space within a borehole. A distributed magnetomotive force sensor is positioned in the annular space and configured to communicate with the surface via a fiber-optic cable. A computer coupled to the fiber-optic cable receives measurements and responsively derives the location of any fluid fronts in the vicinity such as an approaching flood front to enable corrective action before breakthrough. A formation monitoring method includes: injecting a first fluid into a reservoir formation; producing a second fluid from the reservoir formation via a casing in a borehole; collecting magnetic field measurements with a distributed magnetomotive force sensor in an annular space between the casing and the borehole, communicating measurements to a surface interface via one or more fiber-optic cables; and operating on the measurements to locate a front between the first and second fluids.

Abstract: Methods may include estimating the weight fractions of kerogen and inorganic mineral components of at least an interval of a subsurface formation; determining the grain density of kerogen and inorganic mineral components, wherein at least the grain density of kerogen is determined by one or more infrared measurements; and calculating the formation matrix density of at least an interval of the subsurface formation from the estimated weight fractions and the determined grain density.

Abstract: The presence of chlorine and nitrogen are determined and measured using a non-invasive portable neutron-generating and gamma ray detecting system(s). Portable devices of the present invention can also be used to detect chlorine and/or nitrogen-containing underground objects rapidly and on-site. Devices and systems described herein can be operated remotely and pre-programmed with search patterns, guided by an operator remotely, or programmed to home in on high-chlorine and/or nitrogen concentration areas.

Abstract: A method for separating and quantifying gamma ray induced and neutron induced responses in a radiation detector includes detecting radiation in a radiation field comprising neutrons and gamma rays. The detected events are converted into a detector pulse amplitude spectrum. The pulse amplitude spectrum is decomposed into contributions from detected gamma rays and detected neutrons using gamma ray standard spectra and neutron standard spectra and a spectral fitting procedure which results in a best fit between a weighted sum of the contributions and the detector pulse amplitude spectrum. The fitting procedure includes determining fitting parameters for each of the standard spectra wherein at least one of the fitting parameters is different for the gamma ray standard spectra and the neutron standard spectra. In one embodiment, the fitting parameter is spectral gain.

Abstract: Methods are provided for determining the location and height of a fracture in a subterranean formation using pulsed neutron capture (PNC) logging tools. The methods include obtaining a pre-fracture data set, hydraulically fracturing the formation with a slurry that includes a liquid and a proppant in which at least a portion of the proppant is tagged with a thermal neutron absorbing material, obtaining a post-fracture data set, comparing the pre-fracture data set and the post-fracture data set to determine the location of the proppant, and correlating the location of the proppant to a depth measurement of the borehole to determine the location and height of the propped fracture.

Abstract: The present invention is notably directed to computer-implemented methods and systems for recovering an image. Present methods comprise: accessing signal data representing signals; identifying subsets of points arranged so as to span a region of interest as current subsets of points; reconstructing an image based on current subsets of points, by combining signal data associated to the current subsets of points; detecting one or more signal features in a last image reconstructed; for each of the detected one or more signal features, modifying one or more subsets of the current subsets, so as to increase, for each of the modified one or more subsets, a relative number of points at a location of said each of the detected one or more signal features.

Abstract: Systems and methods for estimating absolute elemental concentrations of a subterranean formation from neutron-induced gamma-ray spectroscopy are provided. In one example, a system for estimating an absolute yield of an element in a subterranean formation may include a downhole tool and data processing circuitry. The downhole tool may include a neutron source to emit neutrons into the formation, a neutron monitor to detect a count rate of the emitted neutrons, and a gamma-ray detector to obtain gamma-ray spectra deriving at least in part from inelastic gamma-rays produced by inelastic scattering events and neutron capture gamma-rays produced by neutron capture events. The data processing circuitry may be configured to determine a relative elemental yield from the gamma-ray spectra and to determine an absolute elemental yield based at least in part on a normalization of the relative elemental yield to the count rate of the emitted neutrons.

Abstract: A method of creating three-dimensional borehole data is provided, including illuminating a borehole using collimated beams of electromagnetic radiation; rotating the collimated beams in a sweep of at least 360 degrees; detecting backscattered electromagnetic radiation returned from surfaces of associated illumination planes using electromagnetic radiation sensors; converting detected radiation into a corresponding set of volume image data; analyzing the volume image data using computational visualization processing techniques; and creating a three-dimensional image representative of the volume data.

Abstract: A method of verifying the operational status of a neutron detecting device includes at least partially enclosing a neutron detecting device including a neutron detector in a container having outer walls comprising a thermal neutron absorber material, and determining an attenuated neutron count rate of the neutron detecting device. The method then includes removing the neutron detecting device from the container, exposing the neutron detecting device to neutron radiation originating from cosmic ray background, determining an operational neutron count rate of the neutron detecting device, determining a ratio between the operational neutron count rate and the attenuated neutron count rate, and verifying the operational status of the neutron detecting device if the operational neutron count rate is higher than the attenuated neutron count rate by at least a predetermined amount and the ratio is in a predetermined range.

Abstract: A method of verifying the operational status of a neutron detecting device includes at least partially enclosing a neutron detecting device including a neutron detector in a container having outer walls comprising a thermal neutron absorber material, and determining an attenuated neutron count rate of the neutron detecting device. The method then includes removing the neutron detecting device from the container, exposing the neutron detecting device to neutron radiation originating from cosmic ray background, determining an operational neutron count rate of the neutron detecting device, determining a ratio between the operational neutron count rate and the attenuated neutron count rate, and verifying the operational status of the neutron detecting device if the operational neutron count rate is higher than the attenuated neutron count rate by at least a predetermined amount and the ratio is in a predetermined range.

Abstract: A method of identifying barite in a subterranean annulus that surrounds a wellbore, where the method includes detecting gamma rays in the wellbore that are generated from the annulus, obtaining a count rate of the detected gamma rays, comparing the count rate with reference data, and determining the presence of barite in the wellbore based on the comparison. The count rate can be a ratio of counts of detected gamma rays obtained from spaced apart receivers on a downhole tool, or a ratio of detected inelastic and capture gamma rays. The reference data is obtained by using a simulation algorithm.

Abstract: A multi-source neutron logging tool has been developed. The multi-source logging tool comprises axially aligned gamma and thermal neutron detectors on either side of a multi-neutron source. The multi-source neutron logging tool may be used to evaluate formations adjacent a borehole.

Abstract: 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.

Abstract: A tool activation system and method includes receiving an authorization code of a user to verify access rights of a user to activate the tool. In one example, the authorization code is receive from a smart card. The environment around the tool, which can be in a wellbore, for example, is checked. In response to the authorization code and the checking of the environment, activation of the tool is enabled.

Abstract: A method for estimating a borehole independent porosity of a subterranean formation includes processing a neutron logging data point, preferably including average near and far detector neutron count rates with suitable input data to obtain the porosity estimate. The borehole independent formation porosity may be obtained without any compensation and without any reliance on the measurement or estimation of sensor standoff and/or borehole caliper.

Abstract: An apparatus for estimating porosities of a formation includes: a borehole conveyable pulsed neutron generator to emit a pulse of high energy neutrons; a short spaced neutron detector to provide a count rate as a function of time; a long spaced neutron detector to provide a count rate as a function of time; a timing gate to synchronize a timing of neutrons detected by the detectors with respect to the neutron pulse; and a processor. The processor is configured to determine epithermal count rates and thermal count rates for the detectors based on timing of detection of neutrons with respect to the neutron pulse and calculate a first ratio of short to long spaced detector epithermal count rates and a second ratio of short to long spaced detector thermal count rates. The processor estimates an epithermal porosity using the first ratio and a thermal porosity using the second ratio.

Abstract: A method and apparatus for borehole logging, the method comprising collecting detector output data from a radiation detector of a borehole logging tool, and resolving individual signals in the detector output data by (i) determining a signal form of signals present in the data, (ii) making parameter estimates of one or more parameters of the signals, wherein the one or more parameters comprise at least a signal temporal position, and (iii) determining the energy of each of the signals from at least the signal form and the parameter estimates. The logging tool is shorter, logging tool speed is greater, dwell time is shorter and/or resolution is improved.

Abstract: A liquid scintillation counting system employs a guard detector efficiency compensation system to adjust sample event counts to compensate for a non-ideal guard which may not detect all cosmic and environmental gamma background noise events. The system and method determines counts of events detected coincidently by a guard detector subsystem and a sample detector subsystem in one or more energy regions as well as counts of events that are detected by the sample detector subsystem and not coincidently detected by the guard detector subsystem for the respective energy regions. The system and method calculates correction values for the respective energy regions based on the counts of coincident and non-coincident events and the guard efficiency values associated with the respective energy regions, using, for example, a quenched or unquenched sample. The system then applies the calculated correction values to counts for the respective energy regions, to produce corrected sample event counts.

Abstract: Well logging method and logging tool for measuring cement density and thickness at different azimuth angles for a cemented, cased well. The method uses a gamma source, a short-spaced detector, a long-spaced detector, and preferably a backscatter detector, where the detector-to-source spacings are designed for calculating (93) thickness and density of the cement annulus (94) from the detector count rates (91).

Abstract: Downhole deployable tools for measuring tracer concentrations are disclosed. According to one embodiment, an apparatus comprises a support cable configured to allow the apparatus to be lowered into and raised from a wellbore. A housing is attached to the support cable. The housing includes a detector window on the exterior of the housing. A detector system within the housing includes a detector that measures tracer concentrations. The detector is operably connected to the detector window to direct energy or particles from the detector window to the detector.

Abstract: A disclosed system includes a light source and a nonlinear converter optically coupled to and remote from the light source. The nonlinear light converter converts a light pulse received from the light source to a broadened or spectrum-shifted light pulse. The system also includes a sensor in situ with the nonlinear light converter. The sensor performs a sense operation based on the broadened or spectrum-shifted light pulse and generates an electrical signal corresponding to the sense operation. The system also includes an electro-optical interface in situ with the sensor that transforms the electrical signal to an optical signal for conveyance to a signal collection interface A related method includes generating a light pulse and conveying the light pulse to a remote nonlinear light converter. The method also includes converting the light pulse to a broadened or spectrum-shifted light pulse.

Abstract: Cross-well electromagnetic (EM) imaging is performed using high-power pulsed magnetic field sources, time-domain signal acquisition, low-noise magnetic field sensors, spatial oversampling and super-resolution image enhancement and injected magnetic nanofluids. The acquired signals are processed and inter-well images are generated mapping electromagnetic (EM) signal speed (group velocity) rather than conductivity maps. EM velocity maps with improved resolution for both native and injected fluids are provided.

Abstract: A method for estimating a parameter of interest of an earth formation having a fluid contained in pores of the earth formation, the method includes: conveying a carrier through a borehole penetrating the earth formation; irradiating the earth formation with neutrons from a neutron source disposed at the carrier; measuring radiation emitted from the earth formation resulting from the irradiating using at least one detector; calculating or determining a mathematical parameter from radiation measured by the at least one detector; predicting values of the mathematical parameter over a range of values of an earth formation property; and comparing the mathematical parameter to the predicted values to estimate the parameter of interest.

Abstract: Cross-well electromagnetic (EM) imaging is performed using high-power pulsed magnetic field sources, time-domain signal acquisition, low-noise magnetic field sensors, spatial oversampling and super-resolution image enhancement and injected magnetic nanofluids. Inter-well images are generated mapping electromagnetic (EM) signal speed (group velocity) rather than conductivity maps. EM velocity maps with improved resolution for both native and injected fluids are provided.

Abstract: The present invention provides a device for measuring a mean free path capable of measuring directly the mean free path of a charged particle, a vacuum gauge, and a method for measuring a mean free path. The device for measuring a mean free path according to one embodiment of the invention includes an ion source for generating an ion, a collector (24a) for detecting the number of first charged particles being charged particles having a first flight distance L1 that is a flight distance of zero or more from the ion source, and a collector (24b) for detecting the number of second charged particles having a second flight distance longer than the first flight distance. The control part of the device calculates the mean free path from a ratio between the numbers of the first and second charged particles.

Abstract: Hourly CO2 concentration, amount of solar radiation, and plant distribution information are calculated through observation from predetermined satellites. A concentration of CO2 absorbed by plant-chlorophyll per each time unit is calculated. By adding up the CO2 concentration on the earth and the concentration of CO2 absorbed by the plant-chlorophyll, a CO2 concentration obtained provided that no plant-chlorophyll exist is calculated for a certain period. Thereafter, a mean concentration of CO2 that is absorbed according to changes in the distribution of plant-chlorophyll is calculated on the basis of a monthly mean solar radiation amount and plant-chlorophyll distribution information. By subtracting the CO2 concentration, which is a mean, from the total CO2 concentration, a CO2 concentration, which is a normal, is calculated.

Abstract: Various systems and methods for implementing a directional radiation detection tool are disclosed. One such method involves receiving outputs from several radiation sensors (e.g., gamma ray sensors), which are each facing a different direction. The received outputs are then combined, such that a directional error in one of the outputs is reduced, based upon another one of the outputs.

Abstract: Systems and methods for neutron porosity well logging with high precision and reduced lithology effects are provided. In accordance with an embodiment, a downhole neutron porosity tool may include a neutron source, a neutron monitor, a neutron detector, and data processing circuitry. The neutron source may emit neutrons into a subterranean formation while the neutron monitor detects a count of neutrons proportional to the neutrons emitted. The neutron detector may detect a count of neutrons that scatters off the subterranean formation. The data processing circuitry may determine an environmentally corrected porosity of the subterranean formation based at least in part on the count rate of neutrons scattered off the subterranean formation normalized to the count rate of neutrons proportional to the neutrons emitted by the neutron source.

Abstract: Systems, methods, and devices for determining a porosity of a subterranean formation corrected for borehole effects are provided. One such device may be a downhole tool capable of being lowered into a borehole of a subterranean formation that may include a neutron source, two or more neutron detectors, and data processing circuitry. The neutron source may emit neutrons into the subterranean formation. The two or more neutron detectors may be respectively disposed at two or more azimuthal orientations within the downhole tool, and may detect neutrons scattered by the subterranean formation or borehole fluid in the borehole, or both. Based on the neutrons detected by the neutron detectors, the data processing circuitry may determine a porosity of the subterranean formation corrected for borehole effects.

Abstract: An apparatus for determining fractional amounts of each phase of a multiple phase fluid includes an x-ray generator includes a sample chamber is configured to admit therein a sample of fluid for analysis. The chamber is disposed in a radiation path output from the generator. A filter is disposed in the radiation path between the output of the generator and the radiation input of the sample chamber. A first radiation detector is positioned in a radiation path from the sample chamber after radiation has passed through the sample chamber. A thickness and a material of the filter are selected to optimize resolution of radiation detected by the first detector to changes in volume fraction of oil and water in the fluid sample when a gas fraction thereof is between about 90 to 100 percent.

Abstract: Methods for determining the locations/heights of fractures in a subterranean formation use a post-fracture log obtained with a compensated neutron or pulsed neutron logging tool. Utilizing predetermined relationships between tool count rates and associated near/far count rate ratios, the methods detect the presence of proppant containing high thermal neutron capture cross-section material, substantially eliminating proppant determination uncertainty resulting from changes in formation hydrogen index. In an interval of a well with given borehole and formation conditions, and not containing proppant, a relationship is developed between detector count rate and near/far ratio. This relationship is used to compute count rate from the ratio in intervals of the well possibly containing proppant and which have similar formation and borehole conditions.

Abstract: A method for conducting density measurements in downhole environments corrects for high standoff, by adding a second correction term to the spine and rib method. This second term is a correction based on an apparent standoff estimated using the photo electric effect of the mud. This correction is term depends on the mud properties, both in terms of apparent standoff and correction and therefore requires property calibration for each well. The calibration can be done using the azimuthal information available with LWD tool when the tool is turning. At each depth in homogeneous formation, there can be a succession of density measurements with various tool standoff when the tool is not centered in the borehole. All this information is used to build up a standoff correction fitting perfectly the mud properties.

Abstract: The present invention relates to a well type neutron counter containing a He-3 detector which includes at least one annular gas layer in a polyethylene moderator, which includes a body formed of a neutron moderator and having a sample cavity for inserting a sample of nuclear material therein; and an annular He-3 detector tube including at least one annular gas layer into which at least He-4 or He-3 gas or their mixture is injected and a plurality of anode rods stood in the annular gas layer with an equal spaces, wherein the He-3 detector tube is formed in an inside of the body so as to surround the sample cavity. The neutron counter has a largely reduced size, simplified structure and resultant decreased failure rate as compared to a conventional counter with a large volume.

Abstract: A method for measuring radiation, the method includes selecting at least two radiation detectors, each detector having a spatial resolution that differs from the spatial resolution of other detectors; measuring the radiation with the detectors; and combining a response from at least two of the detectors to produce a composite response exhibiting a spatial resolution.

Abstract: A method for determining the diameter of a wellbore, the wellbore being drilled by a drill string immersed in weighted mud, the weighted mud having a significant weight fraction of a heavy component. A well logging instrument having a gamma ray source and energy-sensitive gamma ray detectors rotates within the wellbore to define a transient interface with a facing portion of the wellbore wall. The instrument measures Compton-effect gamma ray scattering and photoelectric-effect gamma ray scattering of gamma rays that cross a first interface, and of later gamma rays that cross an opposite interface, at each of a plurality of locations along the wellbore to produce a group of gamma ray counts at each of a series of wellbore locations. The counts are used to determine standoffs, weight fraction, and wellbore diameter.

Abstract: A portable mapping tool for use in a horizontal drilling system and associated methods use a boring tool configured for transmitting a locating signal. The mapping tool also includes at least one electromagnetic field detector which is configured for measuring the locating signal from a fixed position proximate to the surface of the ground in a drilling area. The mapping tool includes a housing and a transmitter arrangement supported by the housing for transmitting a setup locating signal for reception by the detector in the region for use in determining certain initial conditions at least prior to drilling. The associated methods include the step of configuring the mapping tool for transmitting a setup locating signal for reception by the detector in the region and using the received setup locating signal in determining certain initial conditions at least prior to drilling.

Abstract: A logging-while-drilling density sensor includes a gamma ray source and at least two NaI detectors spaced apart from the source for determining measurements indicative of the formation density. An acoustic caliper is used for making standoff measurements of the NaI detectors. Measurements made by the detectors are partitioned into standoff bins. An adaptive spine and rib method uses the standoff measurements to obtain density estimates. The method of the invention may also be used with neutron porosity logging devices.

Abstract: For the purpose of reducing artifacts caused by a scan plane tilted with respect to a rotation plane when a multi-row detector is employed, a j-th detector row which an X-ray passing through a pixel point g(x, y) enters is selected based on the distance ?z from a scan center plane to an image reconstruction plane in a z-axis direction and the position (x, y) of the pixel point g in the image reconstruction plane, and data of the j-th detector row is used to determine the pixel value of the pixel point g, where the scan center plane at a certain view angle is defined as an x-y plane, and a direction normal to the x-y plane, i.e., a detector row direction, is defined as the z-axis direction.

Abstract: A method of reconstructing tomography images comprising: acquiring data on individual radiation events; distributing a weight of the individual radiation events along a line of flight associated with the event determined from the acquired data; and iteratively reconstructing the image based on the individually reprojected data.

Abstract: A portable mapping tool for use in a horizontal drilling system and associated methods use a boring tool configured for transmitting a locating signal. The mapping tool also includes at least one electromagnetic field detector which is configured for measuring the locating signal from a fixed position proximate to the surface of the ground in a drilling area. The mapping tool includes a housing and a transmitter arrangement supported by the housing for transmitting a setup locating signal for reception by the detector in the region for use in determining certain initial conditions at least prior to drilling. The associated methods include the step of configuring the mapping tool for transmitting a setup locating signal for reception by the detector in the region and using the received setup locating signal in determining certain initial conditions at least prior to drilling.

Abstract: A portable mapping tool for use in a horizontal drilling system and associated methods use a boring tool configured for transmitting a locating signal. The mapping tool also includes at least one electromagnetic field detector which is configured for measuring the locating signal from a fixed position proximate to the surface of the ground in a drilling area. The mapping tool includes a housing and a transmitter arrangement supported by the housing for transmitting a setup locating signal for reception by the detector in the region for use in determining certain initial conditions at least prior to drilling. The associated methods include the step of configuring the mapping tool for transmitting a setup locating signal for reception by the detector in the region and using the received setup locating signal in determining certain initial conditions at least prior to drilling.

Abstract: We disclose density measurement methods that are accurate over an extended range of standoff distances. One method embodiment includes: a) obtaining a standoff distance, a near detector count rate, and a far detector count rate; b) determining a formation density measurement using near and far detector count rates when the standoff distance is less than a predetermined value; and c) determining the formation density measurement using just the far detector count rate and the standoff distance measurement when the standoff distance is greater than the predetermined value. The method may further include calculating a calibration parameter when the standoff distance is less than the predetermined value. The calibration parameter serves to calibrate a standoff-based correction to the far detector count rate, enabling accurate formation density measurements at large standoff distances. The measurements are made with a rotating logging tool, causing the standoff distance to cycle between large and small values.

Abstract: A method and counter for reducing the background counting rate in gas-filled alpha particle counters wherein the counter is constructed in such a manner as to exaggerate the differences in the features in preamplifier pulses generated by collecting the charges in ionization tracks produced by alpha particles emanating from different regions within the counter and then using pulse feature analysis to recognize these differences and so discriminate between different regions of emanation. Thus alpha particles emitted from the sample can then be counted while those emitted from the counter components can be rejected, resulting in very low background counting rates even from large samples. In one embodiment, a multi-wire ionization chamber, different electric fields are created in different regions of the counter and the resultant difference in electron velocities during charge collection allow alpha particles from the sample and counter backwall to be distinguished.