1、Designation:D627498 (Reapproved 2004) Designation: D6274 10Standard 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,
2、 the year of last revision. A 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
3、 gamma ray(hereafter referred to as gamma) logging of boreholes, wells, access tubes, caissons, or shafts (hereafter referred to as boreholes)as commonly applied to geologic, engineering, ground-water, and environmental (hereafter referred to as geotechnical)investigations. Spectral gamma and loggin
4、g where gamma measurements are 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 adja
5、cent to a borehole with depth (See Fig.1).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. 2).1.3 This guide is restricted to gamma logging with nuclear counters consistin
6、g of scintillation 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,
7、and log quality and interpretation.1.5 To obtain additional information on gamma logs, see Section 13.1.6 This guide is to be used in conjunction with Guide D5753.1.7 Gamma logs should be collected by an operator that is trained in geophysical logging procedures. Gamma logs should beinterpreted by a
8、 professional experienced in log analysis.1.8 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.1.9 This guide does not purport to address all of the safety and liability problems (fo
9、r example, lost or lodged probes andequipment decontamination) associated with its use.1.10 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices
10、 and determine the applicability of regulatorylimitations prior to use.1.11 This guide offers an organized collection of information or a series of options and does not recommend a specific courseof action. This document cannot replace education or experience and should be used in conjunction with p
11、rofessional judgment.Not all aspects of this guide may be applicable in all circumstances. This ASTM standard is not intended to represent or replacethe standard of care by which the adequacy of a given professional service must be judged, nor should this document be appliedwithout consideration of
12、a projects many unique aspects. The word “Standard” in the title of this document means only that thedocument has been approved through the ASTM consensus process.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and Contained FluidsD5088 Practice for Decontaminatio
13、n of Field Equipment Used at Waste SitesD5608 Practices for Decontamination of Field Equipment Used at Low Level Radioactive Waste SitesD5753 Guide for Planning and Conducting Borehole Geophysical LoggingD6167 Guide for Conducting Borehole Geophysical Logging: Mechanical Caliper1This guide is under
14、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 JulyOct. 1, 2004.2010. Published August 2004.March 2011. Originally approved in 1998. Last previous edition approved in 1
15、9982004 asD6274-98.D627498(2004). DOI: 10.1520/D6274-98R04.10.1520/D6274-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on
16、the ASTM website.1This 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 adequately depict all changes accurately, ASTM recommends that users
17、 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, PA 19428-2959, United States.3. Terminology3.1 Definitions:
18、3.1.1 Definitions shall be in accordance with Terminology D653, Section 13, Ref , 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 determined in a controlled environment. Acontrolled environment
19、represents a homogeneous sample volume with known properties.3.2.2 dead time, nthe time after each pulse when a second pulse cannot be detected.3.2.3 dead time effect, nthe inability to distinguish closely-spaced nuclear counts leads to a significant underestimation ofgamma activity in high radiatio
20、n environments and is known as the “dead time effect”.3.2.4 depth of investigation, nthe radial distance from the measurement point to a point where the predominant measuredresponse may be considered centered, which is not to be confused with borehole depth (for example, distance) measured from thes
21、urface.3.2.5 measurement resolution, nthe minimum change in measured value that can be detected.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 is picked t
22、o 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 CanyonD6274 1023.2.6 repeatability, nthe difference in magnitude of two measurements with the same equipment and in the same envir
23、onment.3.2.7 vertical resolution, nthe minimum thickness that can be separated into distinct units.3.2.8 volume of investigation, 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-sph
24、erical and has gradational 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 standardization, procedures, and reports forconducting bor
25、ehole gamma logging.NOTE 1From a study site showing how the gamma logs can be used to identify where beds intersect each of the individual boreholes, demonstratinglateral continuity of the subsurface geology.FIG. 2 Example of Gamma Logs From Two BoreholesD6274 1035. Significance and Use5.1 An approp
26、riately 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 its use include improving selection of gamma logging methods and equipment, gamma log quality andreliabi
27、lity, 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 that personnel (see the Personnel section of Guide D5753) consult up-to-date textbooks and reports on t
28、hegamma technique, application, and interpretation methods.6. Interferences6.1 Most extraneous effects on gamma logs are caused by logging too fast, instrument problems, borehole conditions, andgeologic conditions.6.2 Logging too fast can significantly degrade the quality of gamma logs. Gamma counts
29、 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. 3).6.3 Instrument problems include electrical leakage of cable and grounding problems, degradation of detector efficiencyattri
30、buted to loss of crystal transparency (fogging) or fractures or breaks in the crystal, and mechanical damage causing separationof crystal and photomultiplier tube.6.4 Borehole conditions include changes in borehole diameter (especially in the fluid-filled portion); casing type and number;radioactive
31、 elements in drilling fluid in the borehole, or in cement or slurry behind casing; and steel casing or cement in the annulusaround casing, and thickness of the annulus.6.5 Geologic conditions include high levels of radiation which can degrade the efficiency of gamma counting through the deadtime eff
32、ect, energy level of emitted gammas, formation density, and lithologic bed geometry.7. Apparatus7.1 A geophysical 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
33、 gamma detectors are sodium iodide (NaI).7.2.2 Other gamma detectors include cesium iodide (CsI) and bismuth germanate (BGO).7.3 Gamma probes generate nuclear counts as pulses of voltage that are amplified and clipped to a uniform amplitude.7.3.1Gamma probes used for geotechnical applications typica
34、lly can be logged inside of a 2-in. (5-cm) diameter monitoring well.7.3.1 Gamma probes typically used for geotechnical applications can be logged inside boreholes as small as 2-in. (5-cm) indiameter.7.4 The volume of investigation and depth of investigation are determined by the density of the mater
35、ial near the probe, whichcontrols the average distance a gamma photon can travel before being absorbed.7.4.1 The volume of investigation for gamma logs is generally considered spherical with a radius of 0.5 to 1.0 ft (15 to 30 cm)from the center of the detector in typical geological formations. The
36、volume becomes elongated when detector length exceedsapproximately 0.5 ft (15 cm).7.4.2 The depth of investigation for gamma logs is generally considered to be 0.5 to 1.0 ft (15 to 30 cm).7.5 Vertical resolution of gamma logs is determined by the size of the volume from which gammas can reach a nucl
37、ear detectorsuspended in the borehole. In typical geological formations surrounding a fluid-filled borehole, this is a roughly spherical volumeabout 1 to 2 ft (30 to 60 cm) in diameter. Excessive logging speed can decrease vertical resolution.7.6 Measurement resolution of gamma probes is determined
38、by the counting efficiency of the nuclear detector being used in theprobe. Typical measurement resolution is 1 cps.7.7 Avariety of gamma logging equipment is available for geotechnical investigations. It is not practical to list all of the sourcesof potentially acceptable equipment.8. Calibration an
39、d Standardization of Gamma Logs8.1 General:8.1.1 National Institute of Standards and Technology (NIST) calibration and standardization procedures do not exist for gammalogging.8.1.2 Gamma logs can be used in a qualitative (for example, comparative) or quantitative (for example, estimating radioisoto
40、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,repa
41、ired, and at periodic intervals.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 representative physical model. Calibration data values related tothe physical propert
42、ies (for example, radioisotope concentration) may be recorded in units (for example, cps), that can be convertedD6274 104to units of radioactive element concentration (for example, ppm Radium-226 or percent Uranium-238 equivalents).8.2.1 Calibration is performed by recording gamma log response in cp
43、s in boreholes centered within volumes containing knownhomogenous concentrations of radioactivity elements.8.2.2 Calibration volumes should be designed to contain material as close as possible to that in the environment where the logsare to be obtained to allow for effects such as gamma energy level
44、, formation density, and activity of daughter isotopes on thecalibration process.8.3 Standardization is the process of checking logging response to show evidence of repeatability and consistency, and to ensurethat logging probes with different detector efficiencies measure the same amount of gamma a
45、ctivity in the same formation. Theresponse in cps of every gamma detector is different for the same radioactive environment.8.3.1 Calibration ensures standardization.8.3.2 The American Petroleum Institute maintains a borehole in Houston, Texas, where two formations have been fabricated toprovide hom
46、ogeneous levels of gamma activity so that probes can be standardized on the basis of the response in these boreholes.1 API gamma unit is 1/200thof the full scale response in the representative shale model in this borehole (see Guide D5753).NOTE 1The fluctuations in gamma activity in counts per secon
47、d is shown to vary by progressively smaller amounts as the averaging period (timeconstant) is increased from 1 to 20 s.FIG. 3 Example of Natural Statistical Fluctuation of Gamma Counts From a Test Source of Given StrengthD6274 1058.3.3 For geotechnical applications, gamma logs should be presented in
48、 API units for standardization.8.3.4 A representative borehole may be used to periodically check gamma probe response providing the borehole andsurrounding environment does not change with time or their effects on gamma response can be documented.8.3.5 A small radioactive source(s) (thorium-treated
49、lantern mantles, small bottles of potassium chloride, laboratory radioactivetest sources, or sleeves containing natural radioisotopes (phosphate sands, etc.) placed over the gamma detector can be used tocheck calibration if the sources have been related to a calibration facility.8.4 Gamma log output needs to be corrected for dead time when logging in formations with unusually large count rates, suchas uranium-rich pegmatites or phosphatic sands, and areas contaminated with radioactive waste.8.4.1 Dead time corrections are usually negligible under typical logging c
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