Abstract: A neutron logging tool includes a neutron source and at least one position sensitive thermal or epithermal neutron detector. The logging tool further includes an electronic controller configured to estimate the axial location of detected neutrons. Measurement of the axial neutron flux distribution enables other formation and borehole parameters such as formation porosity and sensor standoff to be computed. In logging while drilling embodiments, a borehole caliper may also be computed form the axial neutron flux distribution.

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: The invention concerns a method for determining the porosity of an earth formation penetrated by a borehole. The method comprises conveying a tool along said borehole, wherein the tool comprises a source of neutron radiation and at least two detectors axially spaced from said source at at least two different spacings. At least one near detector and at least one far detector are selected and a correction computed. The porosity of the earth formation is determined by correcting the far detector porosity with the computed correction.

Abstract: An apparatus for estimating at least one property of an earth formation is disclosed. The apparatus includes: a carrier configured to be disposed in the formation; a neutron tube disposed at the carrier and located on an axis; a high voltage power source disposed in the carrier and electrically connected to the neutron tube, the high voltage power source located remotely from the neutron tube; and at least one detector disposed in the carrier and located proximate to the neutron tube.

Abstract: An apparatus for irradiating an earth formation is disclosed. The apparatus includes: a carrier configured to be disposed in the formation; a neutron tube disposed at the carrier and located on an axis; and a high voltage power source disposed at the carrier and electrically connected to the neutron tube, the high voltage power source being offset from the axis.

Abstract: An apparatus for performing an operation in a borehole penetrating the earth, the apparatus having: a carrier configured for conveyance through the borehole; and a neutron source disposed at the carrier and configured to produce a nuclear fusion reaction that emits a neutron to perform the operation.

Abstract: A C/O ratio is determined using measurements of inelastically scattered gamma rays with a pulsed neutron source. Combined with look-up tables, the C/O measurement is used as an indicator of formation fluid influx into wellbore such as gas kick.

Abstract: An apparatus for estimating a property of an earth formation penetrated by a borehole, the apparatus includes: a carrier configured to be conveyed through the borehole; a neutron source disposed at the carrier and configured to irradiate the earth formation with neutrons; a neutron detector disposed at the carrier and configured to detect neutrons reflected by the earth formation to the detector; a neutron reflector disposed partially around the detector, an area of the detector not covered by the reflector being configured to admit the reflected neutrons; and a neutron absorber disposed at least around the reflector.

Abstract: A downhole tool for performing measurement of a formation. The tool comprising a housing surrounding a source for generating neutrons and a detector for detecting the neutrons. A shield is located outside of, or embedded in, the housing and focuses the neutrons.

Abstract: Example composite materials and calibration assemblies using the same. An example calibration assembly for use in calibrating a downhole formation evaluation tool includes a first body comprising a first material and having a first geometry, a second body comprising a second material formed to receive the first body, wherein the first and second materials and the first geometry are selected so that a calibration property of the calibration assembly substantially matches a corresponding calibration property of a third material.

Abstract: In one aspect of the invention, a downhole tool string component comprises a tubular body with a first and a second tool joint adapted to connect to adjacent tool string components, and a central bore adapted to pass drilling mud between the joints. A sleeve circumferentially disposed about an outer surface of the tubular body. The sleeve is rigidly attached to the outer surface at first and second sleeve ends and forming at least three stabilizer blades. A nuclear source and at least one nuclear detector are disposed within a gap formed between the inner surface of the sleeve and the outer surface of the tubular body.

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: In one aspect of the invention, a downhole tool string component comprises a tubular body with a first and a second tool joint adapted to connect to adjacent tool string components, and a central bore adapted to pass drilling mud between the joints. A sleeve circumferentially disposed about an outer surface of the tubular body. The sleeve is rigidly attached to the outer surface at first and second sleeve ends and forming at least three stabilizer blades. A nuclear source and at least one nuclear detector are disposed within a gap formed between the inner surface of the sleeve and the outer surface of the tubular body.

Abstract: A method and apparatus for processing neutron log data having the steps of a) deriving from the near-spaced neutron count of a neutron logging tool an approximate, unfiltered, lithology-related characteristic of a formation; b) deriving a correction that is essentially independent of the lithology; c) long filtering the correction; and d) adding the resulting, long-filtered correction to the approximate, unfiltered characteristic resulting from step a. in order to derive a compensated characteristic. The method provides statistically good, compensated logs while permitting the use of low activity neutron sources.

Abstract: A method for determining at least one formation property calculated from neutron measurements acquired with a downhole tool includes emitting neutrons from a source in the tool into the formation, detecting neutrons with at least one detector in the downhole tool, calculating a first slowing-down length (L1) based on the detected neutrons, and deriving a second slowing-down length (L2) based on the first slowing-down length (L1). Further steps include deriving a correlation function for relating slowing-down lengths from a first tool to slowing-down lengths associated with a different source, wherein the correlation function depends on formation properties such as bulk density; and applying the correlation function to the slowing-down length of the first tool to derive the slowing-down length of the second tool.

Abstract: A method for fabricating a supermirror for forming a neutron guide. In the method, a neutron supermirror, which is widely used in the formation of thin films in cold neutron guides and the spectrometer field, is fabricated with nickel thin films and titanium thin films, having varying thickness, using a combination of monochromator structures in which nickel thin films and titanium thin films, having the same thickness, are stacked in the form of periodic structures. According to the method, a combination of monochromator structures having a variety of different thicknesses is formed, such that the amount of the overlap of peaks due to the monochromator structures can be adjusted to increase reflectivity, and some of the monochromator structures can be removed during the fabrication of the supermirror to make it easy to extract monochromatic beams, such that it is easy to fabricate a transmission monochromator, rather than a reflection monochromator.

Abstract: In general, in one aspect, the invention relates to a method for evaluating a volcanic reservoir formation having volcanic rock forming elements and a borehole penetrating the volcanic reservoir formation. The method includes controlling chlorine concentration in an environment of the borehole and a tool operation to enable neutron capture spectroscopy measurements of the volcanic rock forming elements, obtaining neutron capture spectroscopy data relating to the volcanic rock forming elements from borehole logging tools, determining a lithology of the volcanic reservoir formation based on at least the neutron capture spectroscopy data, and generating an evaluation of the volcanic reservoir formation based on at least the lithology.

Abstract: A method for determining the location and height of a fracture in a subterranean formation using a neutron emitting logging tool. The method includes obtaining a pre-fracture data set, fracturing the formation with a slurry that includes a proppant doped with a high thermal neutron capture cross-section 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 fracture. Using the PNC tool, it is also possible to determine whether the proppant is located in the fracture, in the borehole adjacent to the fracture, or in both. The method may also include a plurality of post-fracture logging procedures used to determine various fracture and production characteristics in the formation.

Abstract: A neutron generator and method of constructing the same. The generator includes a grid configured to produce an ionizable gas when heated by electrons impinging thereon. A cathode emits electrons to heat the grid and to collide with produced ionizable gas atoms to generate ions. Neutrons are generated from a collision of ions impinging on a target in the generator. A tool for subsurface use incorporating the neutron generator.

Abstract: A neutron generator system is provided that uses substantially only the T-T fusion reaction to generate neutrons for a neutron borehole tool.

Abstract: A nuclear tool includes a tool housing; a neutron generator disposed in the tool housing; and a solid-state neutron monitor disposed proximate the neutron generator for monitoring the output of the neutron generator. A method for constructing a nuclear tool includes disposing a neutron generator in a tool housing; and disposing a solid-state neutron monitor proximate the neutron generator for monitoring the output of the neutron generator.

Abstract: A nuclear tool includes a tool housing; a d-D neutron generator disposed in the tool housing; a d-T neutron generator disposed in the tool housing; and, optionally, a control circuit for controlling pulsing of the d-D neutron generator and the d-T neutron generator. A method for well-logging using a nuclear tool includes disposing the nuclear tool in a wellbore penetrating a formation; pulsing a d-D neutron generator to emit neutrons at a first energy level into the formation; pulsing a d-T neutron generator to emit neutrons at a second energy level into the formation; and measuring signals returning from the formation.

Abstract: A method for determining at least one formation property calculated from neutron measurements acquired with a downhole tool includes emitting neutrons from a source in the tool into the formation, detecting neutrons with at least one detector in the downhole tool, calculating a first slowing-down length (L1) based on the detected neutrons, and deriving a second slowing-down length (L2) based on the first slowing-down length (L1). Further steps include deriving a correlation function for relating slowing-down lengths from a first tool to slowing-down lengths associated with a different source, wherein the correlation function depends on formation properties such as bulk density; and applying the correlation function to the slowing-down length of the first tool to derive the slowing-down length of the second tool.

Abstract: Data acquired using a pulsed nuclear source are susceptible to two sources of error. One error is due to large statistical noise towards the end of an acquisition window. Another source of error is the contamination of the early portion of the data by borehole and other effects. The beginning of the processing window is adjusted based on the signal level at the end of the processing window for the preceding pulsing of the source. The end of the processing window is derived from statistical considerations.

Abstract: An apparatus for logging a formation traversed by a borehole includes a plurality of logging tools adapted for conveyance inside the borehole. The plurality of logging tools includes a tool body, a sensing pad responsive to a density property of the formation coupled to the tool body, a current emitting measure electrode responsive to a lateral resistivity property of the formation incorporated on the sensing pad, a mechanism for urging the sensing pad in contact with a side of the borehole coupled to the tool body, and a pair of mass isolation bands disposed about the tool body to isolate a mass of the tool body adjacent the measure electrode.

Abstract: An apparatus for measuring characteristics of earth formations surrounding a borehole, comprises a resistivity measurement device having a multiplicity of antennae spaced between each other in a longitudinal direction of the apparatus. A neutron measurement device of the apparatus comprises at least a neutron source and at least a neutron detector, each of the neutron detectors being at a distance from the neutron source in the longitudinal direction of the apparatus. The multiplicity of antennae are interleaved with the neutron measurement device in order to reduce a total length of the apparatus and in order to allow a determined area of the earth formation to be measured simultaneously using the neutron measurement device and the resistivity measurement device.

Abstract: The invention concerns radiographic equipment. The equipment includes a source of substantially mono-energetic fast neutrons produced via the deuterium-tritium or deuterium-deuterium fusion reactions, comprising a sealed-tube or similar generator for producing the neutrons. The equipment further includes a source of X-rays or gamma-rays of sufficient energy to substantially penetrate an object to be imaged and a collimating block surrounding the neutron and gamma-ray sources, apart from the provision of one or more slots emitting substantially fan-shaped radiation beams. Further included is a detector array comprising a multiplicity of individual scintillator pixels to receive radiation energy from the sources and convert the received energy into light pulses, the detector array aligned with the fan-shaped beams emitted from the source collimator and collimated to substantially prevent radiation other than that directly transmitted from the sources reaching the array.

Abstract: Measurements made with porosity and density logging tools in a gas reservoir may differ due to invasion effects. The effects are particularly large on measurement-while-drilling applications where invasion is minimal. Using a Monte-Carlo method, a relationship is established between true formation porosity and porosity estimates from density and porosity tools. This relationship is used on real data to get an improved estimate of formation porosity and of gas saturation.

Abstract: A system for detecting neutron radiation. A liquid cocktail mixture comprised of a neutron absorber and a scintillator is housed in a Teflon® tube having a mirror at one end of the tube and a windowed portal at the other end of the tube. Neutrons that penetrate the tube react with the neutron absorber producing ionization that excites a scintillator to produce photons. A photo-multiplier tube is coupled with the windowed portal for receiving photons and converting the photons to electrical signals. A processing device is coupled to the photo-multiplier output for receiving and analyzing the electrical signals so as to provide a measurement pertaining to the presence and relative strength of neutron radiation. The tube can be adapted to function as a portable survey instrument. Alternatively, the tube can be stretched to cover large apertured areas. In such implementations a wavelength shifter is employed to convert light emitted to another wavelength giving a multiplier effect necessary for long light guides.

Abstract: The invention concerns a neutron measurement method for determining porosity of an earth formation surrounding a borehole comprising: conveying a tool along said borehole, wherein said tool comprises a source of neutron radiation and at least one detector axially spaced from said source; generating measured detector response for said at least one detector that is indicative of neutron radiation from said source interacting with said earth formations; operating said measured detector response with a predetermined mathematical equation and thereby obtaining corrected detector response that is independent of the density of said earth formation; and determining porosity of the earth formation surrounding the borehole from said corrected detector response. The invention also relates to a system implementing said method.

Abstract: In the field of wellbore data logging it is known to use isotopic neutron sources in a neutron capture logging technique. However, continuous isotopic sources are unpopular for regulatory and safety reasons. Attempts to employ neutron generator tubes to generate neutron bursts for use in the neutron capture technique have encountered various difficulties in areas connected with signal identification and processing. The disclosure relates to a method of data logging in which a low burst rate neutron generator tube is pulsed at comparatively low rates to generate neutron bursts that are captured in atomic nuclei in a proximal formation. The gamma radiation arising from the neutron capture is detected over a gating intervals defined by temporally distinct points. The gamma detector output is integrated over the gating interval to provide a measure of the decay rate that is independent of the pulse rate. Consequently the signal processing problems do not arise.

Abstract: A borehole logging system for determining bulk density, porosity and formation gas/liquid fluid saturation of formation penetrated by a borehole. Measures of fast neutron radiation and inelastic scatter gamma radiation, induced by a pulsed neutron source, are combined with an iterative numerical solution of a two-group diffusion model to obtain the formation parameters of interest. Double-valued ambiguities in prior art measurements are removed by using the iterative solution of the inverted two-group diffusion model. The system requires two gamma ray detectors at different axial spacings from the source, and a single neutron detector axially spaced between the two gamma ray detectors. The system can be embodied as a wireline system or as a logging-while-drilling system.

Abstract: Techniques for calibrating well-logging sensors comprising emitting a first signal into a first calibration substance disposed proximate to the sensor, measuring a first sensor response from the first signal, emitting a second signal into a second calibration substance disposed proximate to the sensor, measuring a second sensor response from the second signal, and determining a sensor response function from the first sensor response and the second sensor response. One embodiment includes providing a well-logging sensor having a known response function, determining an expected range of a quality check response of the sensor using a quality-check substance with known properties, emitting a quality check signal into the quality-check substance, measuring the quality check response from the quality check signal, and comparing the expected range with the quality check response.

Abstract: Methods and systems for enabling estimations of porosity that are less sensitive to standoff and borehole size effects, and less reliant on corrective techniques for such effects. In one embodiment, a method is provided for estimating porosity of a formation using a downhole neutron tool. The method includes obtaining a near count rate in water, obtaining a far count rate in water, obtaining a near count rate in the formation and a corresponding far count rate in the formation, subtracting the near count rate in water from the near count rate in the formation to form an adjusted near count rate, subtracting the far count rate in water from the far count rate in the formation to form an adjusted far count rate, and estimating a formation porosity value as a function of the adjusted near count rate and the adjusted far count rate.

Abstract: The present invention provides scintillation material having good stability at continuous operating temperatures of at least 175° C. The scintillation material includes a cross linked copolymer with improved aromatic character that form a host plastic having properties of a thermoset polymer. The host plastic contains a primary fluorescent agent and a wavelength shifter. Preferably, the copolymer is comprised of a styrene derivative such as, for example, p-t-butylstyrene, and a higher melting point compound such as, for example, 4-vinylbiphenyl. In accordance with one aspect of the present invention, the scintillation material possesses properties of: good mechanical properties at high temperature (e.g., a Tg of about 180° C.); excellent light output (e.g., energy transfer efficiency); high hydrogen content for fast neutron detection; good optical transparency; and stable operation at temperature.

Abstract: A borehole logging system for determining bulk density, porosity and formation gas/liquid fluid saturation of formation penetrated by a borehole. Measures of fast neutron radiation and inelastic scatter gamma radiation, induced by a pulsed neutron source, are combined with an iterative numerical solution of a two-group diffusion model to obtain the formation parameters of interest. Double-valued ambiguities in prior art measurements are removed by using the iterative solution of the inverted two-group diffusion model. The system requires two gamma ray detectors at different axial spacings from the source, and a single neutron detector axially spaced between the two gamma ray detectors. The system can be embodied as a wireline system or as a logging-while-drilling system.

Abstract: A tool for measuring formation properties in situ. The tool includes a solid state neutron detector and a neutron source disposed on a drill string or wireline. The detector includes a boron carbon surface deposited on a substrate, and the surface can be multi-planar or curved for allowing sensitivity in more than one direction.

Abstract: Methods and systems for enabling estimations of porosity that are less sensitive to standoff and borehole size effects, and less reliant on corrective techniques for such effects. In one embodiment, a method is provided for estimating porosity of a formation using a downhole neutron tool. The method includes obtaining a near count rate in water, obtaining a far count rate in water, obtaining a near count rate in the formation and a corresponding far count rate in the formation, subtracting the near count rate in water from the near count rate in the formation to form an adjusted near count rate, subtracting the far count rate in water from the far count rate in the formation to form an adjusted far count rate, and estimating a formation porosity value as a function of the adjusted near count rate and the adjusted far count rate.

Abstract: A method, of logging a borehole, for use in a cased oil well for detecting the gas/oil or water/oil contact in a hydrocarbon reservoir, using a neutron capture technique to detect one or more properties of fluid includes comparing the count rates from two or more radiation detectors spaced at respective first and second distances from an isotopic source of continuous neutron radiation. The contact detection criteria are arranged to be substantially independent of borehole fluid characteristics. Apparatus (10) for carrying out the method includes a logging tool (10) having an isotopic source (16) and two spaced detectors (17,18).

Abstract: The present invention provides scintillation material having good stability at continuous operating temperatures of at least 175° C. The scintillation material includes a cross linked copolymer with improved aromatic character that form a host plastic having properties of a thermoset polymer. The host plastic contains a primary fluorescent agent and a wavelength shifter. Preferably, the copolymer is comprised of a styrene derivative such as, for example, p-t-butylstyrene, and a higher melting point compound such as, for example, 4-vinylbiphenyl. In accordance with one aspect of the present invention, the scintillation material possesses properties of: good mechanical properties at high temperature (e.g., a Tg of about 180° C.); excellent light output (e.g., energy transfer efficiency); high hydrogen content for fast neutron detection; good optical transparency; and stable operation at temperature.

Abstract: A method is disclosed for measuring neutron interaction properties of an earth formation. The method includes irradiating the formation with bursts of high energy neutrons. The bursts have a duration selected to enable detection of short duration burst related phenomena. After at least one of the bursts, short duration burst related phenomena are measured. After a selected number of the bursts, long duration neutron burst-related phenomena are detected. In some embodiments, the short duration burst related phenomena include at least one of inelastic gamma ray related phenomena, neutron slowing down related phenomena and short capture cross section related phenomena.

Abstract: A method is disclosed for operating a well logging tool having a controllable radiation source operatively coupled to a power source. The method includes monitoring at least one condition in a wellbore, and operatively disconnecting the power source from the radiation source when the at least one condition changes. Also disclosed is a downhole measurement assembly, which includes a radiation source, a power source, and at least one interlock operatively connected between the power source and the radiation source, where the at least one interlock is adapted to selectively arm and disarm the radiation source.

Abstract: A method is disclosed for determining a characteristic of a mud mixture surrounding a drilling tool within a borehole in which a drilling tool is received. The method includes turning the tool in the borehole. Energy is applied into the borehole from an energy source disposed in the tool. Measurement signals are received at a sensor disposed in the tool from a location around the borehole. The cross-section of the borehole is separated into at least a first sector and a second sector. A first measurement signal from the first sector is substantially in response to returning energy which results from the interaction of the applied energy with the mud mixture. A second measurement signal from the second sector is substantially in response to returning energy which results from the interaction of the applied energy with the formation. An indication of an intrinsic characteristic of the mud mixture is derived from the first measurement signals associated with the first sector of the borehole.

Abstract: A borehole logging system for determining bulk density, porosity and formation gas/liquid fluid saturation of formation penetrated by a borehole. Measures of fast neutron radiation and inelastic scatter gamma radiation, induced by a pulsed neutron source, are combined with an iterative numerical solution of a two-group diffusion model to obtain the formation parameters of interest. Double-valued ambiguities in prior art measurements are removed by using the iterative solution of the inverted two-group diffusion model. The system requires two gamma ray detectors at different axial spacings from the source, and a single neutron detector axially spaced between the two gamma ray detectors. The system can be embodied as a wireline system or as a logging-while-drilling system.

Abstract: An improved fast neutron detector fabricated with alternating layers of hydrogenous, optically transparent, non scintillating material and scintillating material. Fast neutrons interact with the hydrogenous material generating recoil protons. The recoil protons enter the scintillating material resulting in scintillations. The detector is optically coupled to a photomultiplier tube which generates electrical pulses proportional in amplitude to the intensity of the scintillations, and therefore are an indication of the energy of the fast neutrons impinging upon the detector. Alternating layers of materials are dimensioned to optimize total efficiency of the detector, or to optimize the spectroscopy efficiency of the detector. The scintillating material is preferably ZnS, and the hydrogenous material is preferably plastic. The detector is ideally suited for well logging applications and fast neutron monitor applications.

Abstract: An improved fast neutron detector fabricated with alternating layers of hydrogenous, optically transparent, non scintillating material and scintillating material. Fast neutrons interact with the hydrogenous material generating recoil protons. The recoil protons enter the scintillating material resulting in scintillations. The detector is optically coupled to a photomultiplier tube which generates electrical pulses proportional in amplitude to the intensity of the scintillations, and therefore are an indication of the energy of the fast neutrons impinging upon the detector. Alternating layers of materials are dimensioned to optimize total efficiency of the detector, or to optimize the spectroscopy efficiency of the detector. The scintillating material is preferably ZnS, and the hydrogenous material is preferably plastic. The detector is ideally suited for well logging applications and fast neutron monitor applications.

Abstract: A method is disclosed for measuring neutron interaction properties of an earth formation. The method includes irradiating the formation with bursts of high energy neutrons. The bursts have a duration selected to enable detection of short duration burst related phenomena. After at least one of the bursts, short duration burst related phenomena are measured. After a selected number of the bursts, long duration neutron burst-related phenomena are detected. In some embodiments, the short duration burst related phenomena include at least one of inelastic gamma ray related phenomena, neutron slowing down related phenomena and short capture cross section related phenomena.

Abstract: A system for measuring the size of a borehole penetrating an earth formation is disclosed. The system uses a neutron source and a least one neutron detector. The neutron detector responds primarily to the composite hydrogen content of material within the borehole and formation upon irradiation by the neutron source. A partition response function is used to delineate the portion of the detector response resulting from borehole and from the formation. Since the detector response from the borehole can be isolated using the partition function and the hydrogen content of the borehole fluid is generally known, the size of the borehole can be determined from borehole response portion of the composite detector response if combined with a neutron porosity measurement of the formation. The neutron porosity measurement can be obtained independently, or by combining the neutron detector response with the response of a second neutron detector at a different axial spacing from the neutron source.

Abstract: Methods and apparatus are disclosed for determining gas saturation, liquid saturation, porosity and density of earth formations penetrated by a well borehole. Determinations are made from measures of fast neutron and inelastic scatter gamma radiation induced by a pulsed, fast neutron source. The system preferably uses two detectors axially spaced from the neutron source. One detector is preferably a scintillation detector responsive to gamma radiation, and a second detector is preferably an organic scintillator responsive to both neutron and gamma radiation. The system can be operated in cased boreholes which are filled with either gas or liquid. Techniques for correcting all measurements for borehole conditions are disclosed.