1、Designation: D6727/D6727M 16Standard Guide forConducting Borehole Geophysical LoggingNeutron1This standard is issued under the fixed designation D6727/D6727M; the number immediately following the designation indicates theyear of original adoption or, in the case of revision, the year of last revisio
2、n. A number in parentheses indicates the year of lastreapproval. A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This guide is focused on the general procedures neces-sary to conduct neutron or neutron porosity (hereafter referredto as neutro
3、n) logging of boreholes, wells, access tubes,caissons, or shafts (hereafter referred to as boreholes) ascommonly applied to geologic, engineering, groundwater andenvironmental (hereafter referred to as geotechnical) explora-tions. Neutron soil moisture measurements made using neutronmoisture gauges,
4、 are excluded. Neutron logging for minerals orpetroleum applications is excluded, along with neutron activa-tion logs where gamma spectral detectors are used to charac-terize the induced gamma activity of minerals exposed toneutron radiation.1.2 This guide defines a neutron log as a record of the ra
5、teat which thermal and epithermal neutrons are scattered back toone or more detectors located on a probe adjacent to a neutronsource.1.2.1 Induction logs are treated quantitatively and should beinterpreted with other logs and data whenever possible.1.2.2 Neutron logs are commonly used to: (1) deline
6、atelithology, and (2) indicate the water-filled porosity of forma-tions (see Fig. 1).1.3 This guide is restricted to neutron logging with nuclearcounters consisting of scintillation detectors (crystals coupledwith photomultiplier tubes), or to He3-tube detectors with orwithout Cd foil covers or coat
7、ings to exclude thermalizedneutrons.1.4 This guide provides an overview of neutron loggingincluding: (1) general procedures; (2) specific documentation;(3 ) calibration and standardization, and (4) log quality andinterpretation.1.5 To obtain additional information on neutron logs seeReferences secti
8、on in this guide.1.6 This guide offers an organized collection of informationor a series of options and does not recommend a specific courseof action. This guide should not be used as a sole criterion forneutron logging and does not replace education, experience,and professional judgment. Neutron lo
9、gging procedures shouldbe adapted to meet the needs of a range of applications andstated in general terms so that flexibility or innovation are notsuppressed. Not all aspects of this guide may be applicable inall circumstances. This ASTM standard is not intended torepresent or replace the standard o
10、f care by which the adequacyof a given professional service must be judged withoutconsideration of a projects many unique aspects. The wordstandard in the title of this document means that the documenthas been approved through the ASTM consensus process.1.7 UnitsThe values stated in either inch-poun
11、d units orSI units given in brackets are to be regarded separately asstandard. The values stated in each system may not be exactequivalents; therefore, each system shall be use independentlyof the other. Combining values from the two systems mayresult in non-conformance with the standard. Add if app
12、ropri-ate: “Reporting of test results in units other than SI shall not beregarded as nonconformance with this standard.”1.8 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-pr
13、iate safety and health practices and determine the applica-bility of regulatory requirements prior to use. The use ofradioactive sources in neutron logging introduces significantsafety issues related to the transportation and handling ofneutron sources, and in procedures to ensure that sources areno
14、t lost or damaged during logging. There are differentrestrictions on the use of radioactive sources in logging indifferent states, and the Nuclear Regulatory Agency (NRC)maintains strict rules and regulations for the licensing ofpersonnel authorized to conduct nuclear source logging.2. Referenced Do
15、cuments2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and ContainedFluids1This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rockand is the direct responsibility of Subcommittee D18.01 on Surface and SubsurfaceCharacterization.Current edition approved Jan. 1, 2016. P
16、ublished January 2016. Originallyapproved in 2001. Last previous edition approved in 2007 as D6727 01(2007).DOI: 10.1520/D6727_D6727M-16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume i
17、nformation, refer to the standards Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1D5088 Practice for Decontamination of Field E
18、quipmentUsed at Waste SitesD5608 Practices for Decontamination of Field EquipmentUsed at Low Level Radioactive Waste SitesD5753 Guide for Planning and Conducting Borehole Geo-physical Logging3. Terminology3.1 Definitions:3.1.1 For definitions of common technical terms in thisstandard, refer to Termi
19、nology D653.3.2 Definitions of Terms Specific to This Standard:3.2.1 depth of exploration, nin geophysics, the radialdistance from the measurement point to a point where thepredominant measured response may be considered centered(not to be confused with depth below the surface).3.2.2 epithermal neut
20、ron, nneutron with kinetic energysomewhat greater than the kinetic energy associated withthermal lattice vibrations of the surrounding formation; suchneutrons have been slowed enough by collisions with forma-tion minerals to interact with the detector, but the population ofepithermal neutrons is not
21、 strongly affected by absorptioncross-sections of trace minerals in the geologic environment.3.2.3 neutron generator, na device which includes aparticle accelerator to generate a flux of high-energy neutrons,and which can be turned on and off through connection with anexternal power supply.3.2.4 neu
22、tron slowing distance, nthe distance traveled bya neutron within a formation over the time required for theneutron to be slowed to half of its original velocity by repeatedcollisions with the atoms in the formation.3.2.5 thermalized neutron, nneutron that has been slowedto a kinetic energy approxima
23、tely equal to that of the thermalkinetic energy of the surrounding formation.3.2.6 volume of exploration, nin geophysics, the volume,which is non-spherical and has gradation boundaries, thatcontributes 90 percent of the measured response and it deter-mined by a combination of theoretical and empiric
24、al modeling.4. Summary of Guide4.1 This guide applies to borehole neutron logging.4.2 This guide briefly describes the significance and use,apparatus, calibration and standardization, procedures, andreports for conducting borehole neutron logging.5. Significance and Use5.1 An appropriately developed
25、, documented, and executedguide is essential for the proper collection and application ofneutron logs.5.2 The benefits of its use include improving selection ofneutron logging methods and equipment; neutron log qualityand reliability; usefulness of the neutron log data for subse-quent display and in
26、terpretation.5.3 This guide applies to commonly used neutron loggingmethods for geotechnical applications.6. Interferences6.1 Most extraneous effects on neutron logs are caused bylogging too fast, instrument problems, borehole conditions,partially saturated formations, and geologic conditions.6.2 Lo
27、gging too fast can significantly degrade the quality ofneutron logs, especially when neutron detectors are designed toASingle detector epithermal neutron log plotted in counts per second.BDual-detector neutron log calibrated in limestone porosity units.CGamma log showing maximum and minimum values u
28、sed as endpoints for the gamma activity scale.DDual detector neutron log plotted in porosity units corrected for the non-effective porosity of clay minerals using the equation:Nc5 N02 Cshshwhere:Nc= corrected neutron log,N0= original neutron log,Csh= computed shale fraction based upon the gamma log
29、position between the endpoints of 10 and 120 cps, andsh= estimate of shale non-effective porosity of about 40 % picked from intervals on the log where sh= 1.0.FIG. 1 Typical Neutron Logs for a Sedimentary Rock EnvironmentD6727/D6727M 162exclude thermalized neutrons, resulting in relatively low count
30、-ing rates. Neutron counts measured at a given depth need to beaveraged over a time interval such that the natural statisticalvariation in the rate of neutron emission is negligible.6.3 Instrument problems include electrical leakage of cableand grounding problems; degradation of detector efficiencya
31、ttributed to loss of crystal transparency (fogging) or fracturesor breaks in the crystal; and mechanical damage causingseparation of crystal and photomultiplier tube.6.4 Borehole conditions include changes in borehole diam-eter; borehole wall roughness whenever neutron logs are rundecentralized; and
32、 steel casing or cement in the annulus aroundcasing, and thickness of the annulus.6.5 Geologic conditions include the presence of clay min-erals with significant non- effective porosity (Fig. 2), and thepresence of minerals such as chlorine with relatively largeneutron absorption cross-sections.6.6
33、Neutron log response is designed to measure water-filled pore spaces so that neutron logs do not measure unsatu-rated porosity.7. Apparatus7.1 A geophysical logging system has been described in thegeneral guide (Section 6, Standard Guide D5753).7.2 Neutron logs are collected with probes using He3det
34、ectors, which may be coated with Cd to exclude thermalizedneutrons, or may be un-coated to detect both thermal andepithermal neutrons; neutron logs may occasionally be col-lected using detectors using lithium-iodide scintillation crystalscoupled to photomultiplier tubes (Fig. 3).7.2.1 A neutron shie
35、ld is needed for the storage of theneutron source during transport to and from the logging site.7.2.2 A secure storage facility is needed for neutron sourceduring the time between logging projects when the sourcecannot be left in the shield in the logging truck.7.2.3 Radiation monitoring equipment i
36、s needed for check-ing of radiation levels outside the neutron shield and inworking areas during use of the neutron source to verify thatradiation hazards do not exist.7.3 Neutron logging probes generate neutron fluxes using achemical radioactive source such as Ca252or a combination ofAm and Be; or
37、by using a neutron generator.7.4 Neutron probes generate nuclear counts as pulses ofvoltage that are amplified and clipped to a uniform amplitude.7.4.1 Neutron probes used for geotechnical applications canbe run centralized or decentralized (held against the side of theborehole); decentralized probe
38、s can be collimated (shielded onthe side away from the borehole wall to reduce the influence ofthe borehole fluid column). However, collimation requires animpracticably heavy, large-diameter logging probe, and suchprobes are rarely used in geotechnical logging (Fig. 3C).7.4.2 Neutron probes can have
39、 a single detector (Fig. 3A),or a pair of detectors located at different separations from theneutron source. When logging probes contain two detectors,the far detector is significantly larger than the near detector tocompensate for the decreasing population of neutrons withdistance from the neutron
40、source, as indicated in Fig. 3B.FIG. 2 Comparison of Single Detector Epithermal Neutron Log with Clay Mineral Fraction Determined Form Core Samples for a Bore-hole in Sedimentary Bedrock (from Keys, 1990)D6727/D6727M 1637.4.3 Neutron probes are designed with source-to-receiverspacing such that measu
41、red neutron counts are proportional tothe slowing down distance of the neutrons, which is assumed tobe inversely proportional to the water-filled porosity of theformation.7.5 The Volume of Exploration and Depth of Explorationare primarily determined by the moisture content of thematerial near the pr
42、obe which controls the average distance aneutron can travel before being absorbed.7.5.1 The Volume of Exploration for neutron logs is gener-ally considered spherical with a radius of 1.5 to 2.5 ft 40 to 70cm from the midpoint between the neutron source anddetector(s) in typical geological formations
43、.7.5.2 The Depth of Exploration for neutron logs is generallyconsidered to be 1.5 to 2.5 ft 40 to 70 cm.7.6 Vertical Resolution of neutron logs is determined by thesize of the volume over which neutrons are scattered backtowards the detector after being emitted by the source. Intypical geological fo
44、rmations surrounding a fluid-filledborehole, this is a roughly spherical volume about 1 to 2 ft 30to 60 cm in diameter. Excessive logging speed can decreasevertical resolution.7.7 Measurement Resolution of neutron probes is deter-mined by the counting efficiency of the nuclear detector ordetectors b
45、eing used in the probe. Typical MeasurementResolution is 1 cps.7.8 A variety of neutron logging equipment is available forgeotechnical investigations. It is not practical to list all of thesources of potentially acceptable equipment.8. Calibration and Standardization of Neutron Logs8.1 General:8.1.1
46、 National Institute of Standards and Technology(NIST) calibration and standardization procedures do not existfor neutron logging.8.1.2 Neutron logs can be used in a qualitative (for example,comparative) or quantitative (for example, estimating water-filled porosity) manner depending upon the project
47、 objectives.8.1.3 Neutron calibration and standardization methods andfrequency shall be sufficient to meet project objectives.8.1.3.1 Calibration and standardization should be performedeach time a neutron probe is suspected to be damaged,modified, repaired, and at periodic intervals.8.2 Calibration
48、is the process of establishing values forneutron response associated with specific values of water-filledporosity in the sampled volume and is accomplished with arepresentative physical model. Calibration data values relatedto the physical properties (for example, formation porosity)may be recorded
49、in units (for example, cps), which can beconverted to units of percent, water-saturated porosity.8.2.1 Calibration is performed by recording neutron logresponse in cps recorded by one or a pair of detectors inboreholes centered within volumes containing a uniform, fullywater-saturated medium of known porosity and mineral com-position.8.2.2 Calibration volumes should be designed to containmaterial as close as possible to that in the environment wherethe logs are to be obtained to allow for effects such as boreholediameter, formation density, and formation che
