ASTM D6274-2018 Standard Guide for Conducting Borehole Geophysical Logging - Gamma.pdf

1、Designation: D6274 10D6274 18Standard Guide forConducting Borehole Geophysical Logging - Gamma1This standard is issued under the fixed designation D6274; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A

2、number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers the general procedures necessary to conduct gamma, natural gamma, total count gamma, or gamma ray(hereafter referred

3、to as gamma) logging of boreholes, wells, access tubes, caissons, or shafts (hereafter referred to as boreholes)as commonly applied to geologic, engineering, groundwater, and environmental (hereafter referred to as geotechnical)investigations. Spectral gamma and logging where gamma measurements are

4、made in conjunction with a nuclear source areexcluded (for example, neutron activation and gamma-gamma density logs). Gamma logging for minerals or petroleumapplications are excluded.1.2 This guide defines a gamma log as a record of gamma activity of the formation adjacent to a borehole with depth (

5、See Fig.1 and Fig. 2).1.2.1 Gamma logs are commonly used to delineate lithology, correlate measurements made on different logging runs, and definestratigraphic correlation between boreholes (See Fig. 23).1.3 This guide is restricted to gamma logging with nuclear counters consisting of scintillation

6、detectors (crystals coupled withphotomultiplier tubes), which are the most common gamma measurement devices used in geotechnical applications.1.4 This guide provides an overview of gamma logging including general procedures, specific documentation, calibration andstandardization, and log quality and

7、 interpretation.1.5 To obtain additional information on gamma logs, see Section 13.1.5 This guide is to be used in conjunction with Guide D5753.1.6 Gamma logs should be collected by an operator that is trained in geophysical logging procedures. Gamma logs should beinterpreted by a professional exper

8、ienced in log analysis.1.7 The geotechnical industry uses English or SI units. The gamma log is typically recorded in units of counts per second (cps)or American Petroleum Institute (API) units.values stated in either SI units or inch-pound units given in brackets are to beregarded separately as sta

9、ndard. The values stated in each system may not be exact equivalents; therefore, each system shall beused independently of the other. Combining values from the two systems may result in nonconformance with the standard.Reporting of test results in units other than SI shall not be regarded as nonconf

10、ormance with this standard.1.7.1 The gamma log is typically recorded in units of counts per second (cps) orAmerican Petroleum Institute (API) units. Thegamma ray API unit is defined as 1200 of the difference between the count rate recorded by a logging tool in the middle of theradioactive bed and th

11、at recorded in the middle of the nonradioactive bed” recorded within the calibration pit.Acalibration facilityfor API units currently exists at the University of Houston and is the world standard for the simple Gamma Ray tool, however thevalidity of the calibration pit has been called into question

12、in recent years.1.9 This guide does not purport to address all of the safety and liability problems (for example, lost or lodged probes andequipment decontamination) associated with its use.1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It

13、is the responsibilityof the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use.1.9 This guide offers an organized collection of information or a series of options and does not r

14、ecommend a specific courseof action. This document cannot replace education or experience and should be used in conjunction with professional judgment.Not all aspects of this guide may be applicable in all circumstances. This ASTM standard is not intended to represent or replace1 This guide is under

15、 the jurisdiction of ASTM Committee D18 on Soil and Rock and is the direct responsibility of Subcommittee D18.01 on Surface and SubsurfaceCharacterization.Current edition approved Oct. 1, 2010Dec. 15, 2018. Published March 2011January 2019. Originally approved in 1998. Last previous edition approved

16、 in 20042010 asD627498(2004).D627410. DOI: 10.1520/D6274-10.10.1520/D6274-18.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequatel

17、y depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken,

18、PA 19428-2959. United States1the standard of care by which the adequacy of a given professional service must be judged, nor should this document be appliedwithout consideration of a projects many unique aspects. The word “Standard” in the title of this document means only that thedocument has been a

19、pproved through the ASTM consensus process.1.10 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World

20、 Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and Contained Fluids2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual

21、Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.NOTE 1This figure demonstrates how the log can be used to identify specific formations, illustrating scale wrap-around for a local gamma peak, andshowing how the contact between two formations

22、is picked to coincide with the half-way point of the transition between the gamma activities of the twoformations.FIG. 1 Example of a Gamma Log From Near the South Rim of the Grand Canyon in the USA (in cps)D6274 182D5088 Practice for Decontamination of Field Equipment Used at Waste SitesD5608 Pract

23、ices for Decontamination of Sampling and Non Sample Contacting Equipment Used at Low Level RadioactiveWaste SitesD5753 Guide for Planning and Conducting Geotechnical Borehole Geophysical LoggingD6167 Guide for Conducting Borehole Geophysical Logging: Mechanical Caliper3. Terminology3.1 Definitions:3

24、.1.1 Definitions shall be in accordance with For definitions of common technical terms used in this standard, refer toTerminology D653, Ref .(1), or as defined below.3.2 Definitions of Terms Specific to This Standard:3.2.1 accuracy, nhow close measured log values approach true value. It is determine

25、d in a controlled environment. Acontrolled environment represents a homogeneous sample volume with known properties.3.2.1 dead time, nthe time after each pulse when a second pulse cannot be detected.FIG. 2 Example of a Gamma Log for the Hydrologic Observation Well KGS #1 Braun located near Hays, Kan

26、sas in the USA (in API unitswhereby SGR reflects the derived total gamma ray log (the sum of all the radiation contributions), and CGR reflects the computedgamma ray log (the sum of the potassium and thorium responses, leaving out the contribution from uranium).D6274 1833.2.2 dead time effect, nthe

27、inability to distinguish closely-spaced nuclear counts leads to a significant underestimation ofgamma activity in high radiation environments and is known as the “dead time effect”.3.2.3 depth of investigation, nthe radial distance from the measurement point to a point where the predominant measured

28、response may be considered centered, which is not to be confused with borehole depth (for example, distance) measured from thesurface.centered.3.2.3.1 DiscussionNOTE 1From a study site showing how the gamma logs can be used to identify where beds intersect each of the individual boreholes, demonstra

29、tinglateral continuity of the subsurface geology.FIG. 23 Example of Gamma Logs From Two BoreholesD6274 184The depth of investigation for borehole logging is a radial distance from the borehole and is not to be confused with borehole depthor any depth measured from the surface.3.2.4 measurement resol

30、ution, nthe minimum change in measured value that can be detected.3.2.6 repeatability, nthe difference in magnitude of two measurements with the same equipment and in the same environment.3.2.5 vertical resolution, nthe minimum thickness that can be separated into distinct units.3.2.6 volume of inve

31、stigation, nthe volume that contributes 90 % of the measured response. It is determined by a combinationof theoretical and empirical modeling. The volume of investigation is non-spherical and has gradational boundaries.3.2.6.1 DiscussionIt is determined by a combination of theoretical and empirical

32、modeling. The volume of investigation is non-spherical and hasgradational boundaries.4. Summary of Guide4.1 This guide applies to borehole gamma logging and is to be used in conjunction with Guide D5753.4.2 This guide briefly describes the significance and use, apparatus, calibration and standardiza

33、tion, procedures, and reports forconducting borehole gamma logging.5. Significance and Use5.1 An appropriately developed, documented, and executed guide is essential for the proper collection and application of gammalogs. This guide is to be used in conjunction with Guide D5753.5.2 The benefits of i

34、ts use include improving selection of gamma logging methods and equipment, gamma log quality andreliability, and usefulness of the gamma log data for subsequent display and interpretation.5.3 This guide applies to commonly used gamma logging methods for geotechnical applications.5.4 It is essential

35、that personnel (see the Personnel section of Guide D5753) consult up-to-date textbooks and reports on thegamma technique, application, and interpretation methods.6. Interferences6.1 Most extraneous effects on gamma logs are caused by logging too fast, instrument problems, borehole conditions, andgeo

36、logic conditions.6.2 Logging too fast can significantly degrade the quality of gamma logs. Gamma counts originating at a given depth need tobe averaged over a time interval such that the natural statistical variation in the rate of gamma photon emission is negligible (seeFig. 34).6.3 Instrument prob

37、lems include include: a) electrical leakage of cable and grounding problems, b) degradation of detectorefficiency attributed to loss of crystal transparency (fogging) or fractures or breaks in the crystal, and c) mechanical damagecausing separation of crystal and photomultiplier tube.6.4 Borehole co

38、nditions include include: a) changes in borehole diameter (especially in the fluid-filled portion); portion), b)casing type and number; number, c) radioactive elements in drilling fluid in the borehole, or in cement or slurry behind casing;andcasing, d) steel casing or cement in the annulus around c

39、asing, and e) thickness of the annulus.annulus around casing.6.5 Geologic conditions include high levels of radiation which can degrade the efficiency of gamma counting through the deadtime effect, energy level of emitted gammas, formation density, and lithologic bed geometry.7. Apparatus7.1 A geoph

40、ysical logging system has been described in the general guide (the Apparatus section of Guide D5753).7.2 Gamma logs are collected with probes using scintillation detectors.7.2.1 The most common gamma detectors are sodium iodide (NaI).7.2.2 Other gamma detectors include cesium iodide (CsI) and bismut

41、h germanate (BGO).7.3 Gamma probes generate nuclear counts as pulses of voltage that are amplified and clipped to a uniform amplitude.7.3.1 Gamma probes typically used for geotechnical applications can be logged inside boreholes as small as 2-in. (5-cm) 5 cm2-in. in diameter.7.4 The volume of invest

42、igation and depth of investigation are determined by the density of the material near the probe, whichcontrols the average distance a gamma photon can travel before being absorbed.D6274 1857.4.1 The volume of investigation for gamma logs is generally considered spherical with a radius of 0.5 to 1.0

43、ft (15 to 30 cm)15to 30 cm 0.5 to 1.0 ft from the center of the detector in typical geological formations. The volume becomes elongated whendetector length exceeds approximately 0.5 ft (15 cm).15 cm 0.5 ft.7.4.2 The depth of investigation for gamma logs is generally considered to be 0.5 to 1.0 ft (1

44、5 to 30 cm).15 to 30 cm 0.5 to1.0 ft.7.5 Vertical resolution of gamma logs is determined by the size of the volume from which gammas can reach a nuclear detectorsuspended in the borehole. In typical geological formations surrounding a fluid-filled borehole, this is a roughly spherical volumeabout 1

45、to 2 ft (30 to 60 cm)30 to 60 cm 1 to 2 ft in diameter. Excessive logging speed can decrease vertical resolution.7.6 Measurement resolution of gamma probes is determined by the counting efficiency of the nuclear detector being used in theprobe. Typical measurement resolution is 1 cps.7.7 Avariety of

46、 gamma logging equipment is available for geotechnical investigations. It is not practical to list all of the sourcesof potentially acceptable equipment.NOTE 1The fluctuations in gamma activity in counts per second is shown to vary by progressively smaller amounts as the averaging period (timeconsta

47、nt) is increased from 1 to 20 s.FIG. 34 Example of Natural Statistical Fluctuation of Gamma Counts From a Test Source of Given StrengthD6274 1868. Calibration and Standardization of Gamma Logs8.1 General:8.1.1 National Institute of Standards and Technology (NIST) calibration and standardization proc

48、edures do not exist for gammalogging. A calibration facility for API units currently exists at the University of Houston and is the world standard for the simpleGamma Ray tool.8.1.2 Gamma logs can be used in a qualitative (for example, comparative) or quantitative (for example, estimating radioisoto

49、peconcentration) manner depending upon the project objectives.8.1.3 Gamma calibration and standardization methods and frequency shall be sufficient to meet project objectives.8.1.3.1 Calibration and standardization should be performed each time a gamma probe is suspected to be damaged, modified,repaired, and at periodic intervals.but at least once a year.8.2 Calibration is the process of establishing values for gamma response associated with specific levels of radioisotopeconcentration in the sampled volume and is accomplished with a representati