1、Designation: D 6727 01 (Reapproved 2007)Standard Guide forConducting Borehole Geophysical LoggingNeutron1This standard is issued under the fixed designation D 6727; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last r
2、evision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide is focused on the general procedures neces-sary to conduct neutron or neutron porosity (hereafter referredto as
3、neutron) logging of boreholes, wells, access tubes,caissons, or shafts (hereafter referred to as boreholes) ascommonly applied to geologic, engineering, ground-water andenvironmental (hereafter referred to as geotechnical) investi-gations. Neutron soil moisture measurements made usingneutron moistur
4、e gauges, are excluded. Neutron logging forminerals or petroleum applications is excluded, along withneutron activation logs where gamma spectral detectors areused to characterize the induced gamma activity of mineralsexposed to neutron radiation.1.2 This guide defines a neutron log as a record of t
5、he rateat 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) d
6、elineatelithology, 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
7、 coatings 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 s
8、ection in this guide.1.6 This guide is to be used in conjunction with StandardGuide D 5753.1.7 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 do
9、es not replace education, experience,and professional judgment. Neutron logging 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
10、. This ASTM standard is not intended torepresent or replace the standard of 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
11、 the ASTM consensus process.1.8 The geotechnical industry uses English or SI units. Theneutron log is typically recorded in units of counts per second(cps) or in percent porosity.1.9 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is therespon
12、sibility of the user of this standard to establish appro-priate 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 ofneut
13、ron sources, and in procedures to insure that sources arenot 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 au
14、thorized to conduct nuclear source logging.2. Referenced Documents2.1 ASTM Standards:2D 420 Guide to Site Characterization for Engineering De-sign and Construction PurposesD 653 Terminology Relating to Soil, Rock, and ContainedFluidsD 5088 Practices for Decontamination of Field EquipmentUsed at Wast
15、e SitesD 5608 Practices for Decontamination of Field EquipmentUsed at Low Level Radioactive Waste SitesD 5730 Guide for Site Characterization for Environmental1This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rockand is the direct responsibility of Subcommittee D18.01 on Surface
16、 and SubsurfaceCharacterization.Current edition approved July 1, 2007. Published August 2007. Originallyapproved in 2001. Last previous edition approved in 2001 as D 6727 01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For
17、Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Purposes With Emphasis on Soil, Rock, the Vadose Zoneand Ground WaterD 5
18、753 Guide for Planning and Conducting Borehole Geo-physical LoggingD 6167 Guide for Conducting Borehole Geophysical Log-ging: Mechanical CaliperD 6235 Practice for Expedited Site Characterization ofVadose Zone and Ground Water Contamination at Hazard-ous Waste Contaminated SitesD 6274 Guide for Cond
19、ucting Borehole Geophysical Log-ging - GammaD 6429 Guide for Selecting Surface Geophysical Methods3. Terminology3.1 DefinitionsDefinitions shall be in accordance withTerminology D 653, Section 13 Ref 1, or as defined below.3.2 Definitions of Terms Specific to This Standard:3.2.1 accuracy, nhow close
20、 measured log values ap-proach true value. It is determined in a controlled environment.A controlled environment represents a homogeneous samplevolume with known properties.3.2.2 depth of investigation, nthe radial distance from themeasurement point to a point where the predominant measuredresponse
21、may be considered centered, which is not to beconfused with borehole depth (for example, distance) mea-sured from the surface.3.2.3 effective porosity, nthe volume percent of connectedpore spaces within a formation that are capable of conductingground-water flow.3.2.4 epithermal neutron, nneutron wi
22、th 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 strongly affect
23、ed by absorptioncross-sections of trace minerals in the geologic environment.3.2.5 measurement resolution, nthe minimum change inmeasured value that can be detected.3.2.6 neutron generator, na device which includes aparticle accelerator to generate a flux of high-energy neutrons,and which can be tur
24、ned on and off through connection with anexternal power supply.3.2.7 neutron 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.3.2.8 repeata
25、bility, nthe difference in magnitude of twomeasurements with the same equipment and in the sameenvironment.3.2.9 thermalized neutron, nneutron that has been slowedto a kinetic energy approximately equal to that of the thermalkinetic energy of the surrounding formation.3.2.10 total porosity, nthe tot
26、al amount of pore spaceexpressed as a volume fraction in percent in a formation; thistotal consists of effective pore space which can conductground-water flow, and additional unconnected pores that willnot conduct ground-water.3.2.11 vertical resolution, nthe minimum thickness thatcan be separated i
27、nto distinct units.3.2.12 volume of investigation, nthe volume that contrib-utes 90 percent of the measured response. It is determined bya combination of theoretical and empirical modeling. Thevolume of investigation is non-spherical and has gradationalboundaries.4. Summary of Guide4.1 This guide ap
28、plies to borehole neutron logging and is tobe used in conjunction with Standard Guide D 5753.ASingle 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 used as endpoints for the
29、gamma activity scale.DDual detector neutron log plotted in porosity units corrected for the non-effective porosity of clay minerals using the equation:Nc5 N0 Csh Fshwhere:Nc= corrected neutron log,N0= original neutron log,Csh= computed shale fraction based upon the gamma log position between the end
30、points of 10 and 120 cps, andFsh= estimate of shale non-effective porosity of about 40 % picked from intervals on the log where Fsh= 1.0.FIG. 1 Typical Neutron Logs for a Sedimentary Rock EnvironmentD 6727 01 (2007)24.2 This guide briefly describes the significance and use,apparatus, calibration and
31、 standardization, procedures, andreports for conducting borehole neutron logging.5. Significance and Use5.1 An appropriately developed, documented, and executedguide is essential for the proper collection and application ofneutron logs. This guide is to be used in conjunction withStandard Guide D 57
32、53.5.2 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 interpretation.5.3 This guide applies to commonly used neutron loggingmethods for geotechnical applic
33、ations.5.4 It is essential that personnel (see Section 8.3.2, StandardGuide D 5753) consult up-to-date textbooks and reports on theneutron technique, application, and interpretation methods.6. Interferences6.1 Most extraneous effects on neutron logs are caused bylogging too fast, instrument problems
34、, borehole conditions,partially saturated formations, and geologic conditions.6.2 Logging too fast can significantly degrade the quality ofneutron logs, especially when neutron detectors are designed toexclude thermalized neutrons, resulting in relatively low count-ing rates. Neutron counts measured
35、 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 efficiencyattributed to loss of crystal transp
36、arency (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 steel casing or cement in the annu
37、lus 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 Neutron log response is designed to
38、 measure water-filled pore spaces so that neutron logs do not measure unsat-urated porosity.7. Apparatus7.1 A geophysical logging system has been described in thegeneral guide (Section 6, Standard Guide D 5753).7.2 Neutron logs are collected with probes using He3detectors, which may be coated with C
39、d 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 shield is needed for the storage of th
40、eneutron 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 is needed for check-ing of radiatio
41、n levels outside the neutron shield and inworking areas during use of the neutron source to verify thatradiation hazards do not exist.FIG. 2 Comparison of Single Detector Epithermal Neutron Log with Clay Mineral Fraction Determined Form Core Samples for aBorehole in Sedimentary Bedrock (from Keys, 1
42、990)D 6727 01 (2007)37.3 Neutron logging probes generate neutron fluxes using achemical radioactive source such as Ca252or a combination ofAm and Be; or 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
43、.4.1 Neutron probes used for geotechnical applications canbe run centralized or decentralized (held against the side of theborehole); decentralized probes can be collimated (shielded onthe side away from the borehole wall to reduce the influence ofthe borehole fluid column). However, collimation req
44、uires animpracticably heavy, large-diameter logging probe, and suchprobes are rarely used in geotechnical logging (Fig. 3C).7.4.2 Neutron probes can have a single detector (Fig. 3A),or a pair of detectors located at different separations from theneutron source. When logging probes contain two detect
45、ors,the far detector is significantly larger than the near detector tocompensate for the decreasing population of neutrons withdistance from the neutron source, as indicated in Fig. 3B.7.4.3 Neutron probes are designed with source-to-receiverspacing such that measured neutron counts are proportional
46、 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 Investigation and Depth of Investigationare primarily determined by the moisture content of thematerial near the probe which controls the average
47、distance aneutron can travel before being absorbed.7.5.1 The Volume of Investigation for neutron logs isgenerally considered spherical with a radius of 1.5 to 2.5 ft (40to 70 cm) from the midpoint between the neutron source anddetector(s) in typical geological formations.7.5.2 The Depth of Investiga
48、tion for neutron logs is gener-ally considered 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 formations surrounding a
49、fluid-filled bore-hole, this is a roughly spherical volume about 1 to 2 ft (30 to60 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 being 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
