ASTM D6274-98(2004)
(Guide)Standard Guide for Conducting Borehole Geophysical Logging-Gamma
Standard Guide for Conducting Borehole Geophysical Logging-Gamma
SIGNIFICANCE AND USE
An appropriately developed, documented, and executed guide is essential for the proper collection and application of gamma logs. This guide is to be used in conjunction with Guide D 5753.
The benefits of its use include improving selection of gamma logging methods and equipment, gamma log quality and reliability, and usefulness of the gamma log data for subsequent display and interpretation.
This guide applies to commonly used gamma logging methods for geotechnical applications.
It is essential that personnel (see the Personnel section of Guide D 5753) consult up-to-date textbooks and reports on the gamma technique, application, and interpretation methods.
SCOPE
1.1 This guide covers the general procedures necessary to conduct gamma, natural gamma, total count gamma, or 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 logging where gamma measurements are made in conjunction with a nuclear source are excluded (for example, neutron activation and gamma-gamma density logs). Gamma logging for mineral or petroleum applications 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 (See Fig.1).
1.2.1 Gamma logs are commonly used to: delineate lithology, correlate measurements made on different logging runs, and define stratigraphic correlation between boreholes (See Fig. 2).
1.3 This guide is restricted to gamma logging with nuclear counters consisting of scintillation detectors (crystals coupled with photomultiplier tubes), which are the most common gamma measurement devices used in geotechnical application.
1.4 This guide provides an overview of gamma logging including: general procedures; specific documentation; calibration and standardization, 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 D 5753.
1.7 Gamma logs should be collected by an operator that is trained in geophysical logging procedures. Gamma logs should be interpreted by a 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.
This guide does not purport to address all of the safety and liability problems (for example, lost or lodged probes and equipment 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 responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
1.11 This guide offers an organized collection of information or a series of options and does not recommend a specific course of action. This document cannot replace education or judgment. Not all aspects of this guide may be applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied without consideration of a project's many unique aspects. The word "Standard" in the title of this document means only that the document has been approved through the ASTM consensus process.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:D6274–98 (Reapproved 2004)
Standard Guide for
Conducting Borehole Geophysical Logging - Gamma
This standard is issued under the fixed designation D6274; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.9 This guide does not purport to address all of the safety
and liability problems (for example, lost or lodged probes and
1.1 This guide covers the general procedures necessary to
equipment decontamination) associated with its use.
conductgamma,naturalgamma,totalcountgamma,orgamma
1.10 This standard does not purport to address all of the
ray (hereafter referred to as gamma) logging of boreholes,
safety concerns, if any, associated with its use. It is the
wells, access tubes, caissons, or shafts (hereafter referred to as
responsibility of the user of this standard to establish appro-
boreholes) as commonly applied to geologic, engineering,
priate safety and health practices and determine the applica-
ground-water, and environmental (hereafter referred to as
bility of regulatory limitations prior to use.
geotechnical) investigations. Spectral gamma and logging
1.11 This guide offers an organized collection of informa-
where gamma measurements are made in conjunction with a
tion or a series of options and does not recommend a specific
nuclear source are excluded (for example, neutron activation
course of action. This document cannot replace education or
andgamma-gammadensitylogs).Gammaloggingforminerals
experienceandshouldbeusedinconjunctionwithprofessional
or petroleum applications are excluded.
judgment. Not all aspects of this guide may be applicable in all
1.2 This guide defines a gamma log as a record of gamma
circumstances. This ASTM standard is not intended to repre-
activityoftheformationadjacenttoaboreholewithdepth(See
sent or replace the standard of care by which the adequacy of
Fig. 1).
a given professional service must be judged, nor should this
1.2.1 Gamma logs are commonly used to delineate lithol-
document be applied without consideration of a project’s many
ogy, correlate measurements made on different logging runs,
unique aspects. The word “Standard” in the title of this
and define stratigraphic correlation between boreholes (See
document means only that the document has been approved
Fig. 2).
through the ASTM consensus process.
1.3 This guide is restricted to gamma logging with nuclear
counters consisting of scintillation detectors (crystals coupled
2. Referenced Documents
with photomultiplier tubes), which are the most common
2.1 ASTM Standards:
gamma measurement devices used in geotechnical applica-
D653 Terminology Relating to Soil, Rock, and Contained
tions.
Fluids
1.4 This guide provides an overview of gamma logging
D5088 Practice for Decontamination of Field Equipment
including general procedures, specific documentation, calibra-
Used at Waste Sites
tion and standardization, and log quality and interpretation.
D5608 Practices for Decontamination of Field Equipment
1.5 To obtain additional information on gamma logs, see
Used at Low Level Radioactive Waste Sites
Section 13.
D5753 Guide for Planning and Conducting Borehole Geo-
1.6 This guide is to be used in conjunction with Guide
physical Logging
D5753.
D6167 Guide for Conducting Borehole Geophysical Log-
1.7 Gamma logs should be collected by an operator that is
ging: Mechanical Caliper
trainedingeophysicalloggingprocedures.Gammalogsshould
be interpreted by a professional experienced in log analysis.
3. Terminology
1.8 The geotechnical industry uses English or SI units. The
3.1 Definitions:
gamma log is typically recorded in units of counts per second
3.1.1 Definitions shall be in accordance with Terminology
(cps) or American Petroleum Institute (API) units.
D653, Section 13, Ref (1), or as defined below.
3.2 Definitions of Terms Specific to This Standard:
ThisguideisunderthejurisdictionofASTMCommitteeD18onSoilandRock
and is the direct responsibility of Subcommittee D18.01 on Surface and Subsurface
Characterization. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved July 1, 2004. Published August 2004. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1998. Last previous edition approved in 1998 as D6274 - 98. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D6274-98R04. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6274–98 (2004)
NOTE 1—This figure demonstrates how the log can be used to identify specific formations, illustrating scale wrap-around for a local gamma peak, and
showing how the contact between two formations is picked to coincide with the half-way point of the transition between the gamma activities of the two
formations.
FIG. 1 Example of a Gamma Log From Near the South Rim of the Grand Canyon
3.2.1 accuracy, n—how close measured log values ap- 3.2.4 depth of investigation, n—the radial distance from the
proachtruevalue.Itisdeterminedinacontrolledenvironment. measurement point to a point where the predominant measured
A controlled environment represents a homogeneous sample response may be considered centered, which is not to be
volume with known properties. confused with borehole depth (for example, distance) mea-
3.2.2 dead time, n—thetimeaftereachpulsewhen a second sured from the surface.
pulse cannot be detected. 3.2.5 measurement resolution, n—the minimum change in
3.2.3 dead time effect, n—the inability to distinguish measured value that can be detected.
closely-spaced nuclear counts leads to a significant underesti- 3.2.6 repeatability, n—the difference in magnitude of two
mation of gamma activity in high radiation environments and measurements with the same equipment and in the same
is known as the “dead time effect”. environment.
D6274–98 (2004)
NOTE 1—From a study site showing how the gamma logs can be used to identify where beds intersect each of the individual boreholes, demonstrating
lateral continuity of the subsurface geology.
FIG. 2 Example of Gamma Logs From Two Boreholes
3.2.7 vertical resolution, n—the minimum thickness that 4.2 This guide briefly describes the significance and use,
can be separated into distinct units. apparatus, calibration and standardization, procedures, and
3.2.8 volume of investigation, n—the volume that contrib- reports for conducting borehole gamma logging.
utes 90 % of the measured response. It is determined by a
5. Significance and Use
combination of theoretical and empirical modeling. The vol-
5.1 An appropriately developed, documented, and executed
ume of investigation is non-spherical and has gradational
guide is essential for the proper collection and application of
boundaries.
gammalogs.ThisguideistobeusedinconjunctionwithGuide
4. Summary of Guide
D5753.
4.1 This guide applies to borehole gamma logging and is to 5.2 The benefits of its use include improving selection of
be used in conjunction with Guide D5753. gamma logging methods and equipment, gamma log quality
D6274–98 (2004)
and reliability, and usefulness of the gamma log data for to be averaged over a time interval such that the natural
subsequent display and interpretation. statistical variation in the rate of gamma photon emission is
5.3 This guide applies to commonly used gamma logging
negligible (see Fig. 3).
methods for geotechnical applications.
6.3 Instrument problems include electrical leakage of cable
5.4 It is essential that personnel (see the Personnel section
and grounding problems, degradation of detector efficiency
of Guide D5753) consult up-to-date textbooks and reports on
attributed to loss of crystal transparency (fogging) or fractures
the gamma technique, application, and interpretation methods.
or breaks in the crystal, and mechanical damage causing
separation of crystal and photomultiplier tube.
6. Interferences
6.4 Borehole conditions include changes in borehole diam-
6.1 Most extraneous effects on gamma logs are caused by
eter (especially in the fluid-filled portion); casing type and
loggingtoofast,instrumentproblems,boreholeconditions,and
number; radioactive elements in drilling fluid in the borehole,
geologic conditions.
orincementorslurrybehindcasing;andsteelcasingorcement
6.2 Logging too fast can significantly degrade the quality of
gamma logs. Gamma counts originating at a given depth need in the annulus around casing, and thickness of the annulus.
NOTE 1—The fluctuations in gamma activity in counts per second is shown to vary by progressively smaller amounts as the averaging period (time
constant) is increased from 1 to 20 s.
FIG. 3 Example of Natural Statistical Fluctuation of Gamma Counts From a Test Source of Given Strength
D6274–98 (2004)
6.5 Geologic conditions include high levels of radiation concentration in the sampled volume and is accomplished with
which can degrade the efficiency of gamma counting through arepresentativephysicalmodel.Calibrationdatavaluesrelated
the dead time effect, energy level of emitted gammas, forma- to the physical properties (for example, radioisotope concen-
tion density, and lithologic bed geometry. tration)mayberecordedinunits(forexample,cps),thatcanbe
converted to units of radioactive element concentration (for
7. Apparatus
example, ppm Radium-226 or percent Uranium-238 equiva-
7.1 Ageophysical logging system has been described in the
lents).
general guide (the Apparatus section of Guide D5753).
8.2.1 Calibration is performed by recording gamma log
7.2 Gamma logs are collected with probes using scintilla-
response in cps in boreholes centered within volumes contain-
tion detectors.
ing known homogenous concentrations of radioactivity ele-
7.2.1 The most common gamma detectors are sodium io-
ments.
dide (NaI).
8.2.2 Calibration volumes should be designed to contain
7.2.2 Other gamma detectors include cesium iodide (CsI)
material as close as possible to that in the environment where
and bismuth germanate (BGO).
the logs are to be obtained to allow for effects such as gamma
7.3 Gamma probes generate nuclear counts as pulses of
energy level, formation density, and activity of daughter
voltage that are amplified and clipped to a uniform amplitude.
isotopes on the calibration process.
7.3.1 Gamma probes used for geotechnical applications
8.3 Standardization is the process of checking logging
typically can be logged inside of a 2-in. (5-cm) diameter
response to show evidence of repeatability and consistency,
monitoring well.
and to ensure that logging probes with different detector
7.4 The volume of investigation and depth of investigation
efficiencies measure the same amount of gamma activity in the
are determined by the density of the material near the probe,
same formation. The response in cps of every gamma detector
whichcontrolstheaveragedistanceagammaphotoncantravel
is different for the same radioactive environment.
before being absorbed.
8.3.1 Calibration ensures standardization.
7.4.1 The volume of investigation for gamma logs is gen-
8.3.2 The American Petroleum Institute maintains a bore-
erally considered spherical with a radius of 0.5 to 1.0 ft (15 to
hole in Houston, Texas, where two formations have been
30 cm) from the center of the detector in typical geological
fabricatedtoprovidehomogeneouslevelsofgammaactivityso
formations. The volume becomes elongated when detector
that probes can be standardized on the basis of the response in
th
length exceeds approximately 0.5 ft (15 cm).
these boreholes. 1 API gamma unit is 1/200 of the full scale
7.4.2 Thedepthofinvestigationforgammalogsisgenerally
response in the representative shale model in this borehole (see
considered to be 0.5 to 1.0 ft (15 to 30 cm).
Guide D5753).
7.5 Vertical resolution of gamma logs is determined by the
8.3.3 For geotechnical applications, gamma logs should be
size of the volume from which gammas can reach a nuclear
presented in API units for standardization.
detector suspended in the borehole. In typical geological
8.3.4 Arepresentative borehole may be used to periodically
formations surrounding a fluid-filled borehole, this is a roughly
check gamma probe response providing the borehole and
spherical volume about 1 to 2 ft (30 to 60 cm) in diameter.
surrounding environment does not change with time or their
Excessive logging speed can decrease vertical resolution.
effects on gamma response can be documented.
7.6 Measurement resolution of gamma probes is determined
8.3.5 Asmall radioactive source(s) (thorium-treated lantern
by the counting efficiency of the nuclear detector being used in
mantles, small bottles of potassium chloride, laboratory radio-
the probe. Typical measurement resolution is 1 cps.
active test sources, or sleeves containing natural radioisotopes
7.7 A variety of gamma logging equipment is available for
(phosphatesands,etc.))placedoverthegammadetectorcanbe
geotechnical investigations. It is not practical to list all of the
used to check calibration if the sources have been related to a
sources of potentially acceptable equipment.
calibration facility.
8.4 Gamma log output needs to be corrected for dead time
8. Calibration and Standardization of Gamma Logs
when logging in formations with unusually large count rates,
8.1 General:
suchasuranium-richpegmatitesorphosphaticsands,andareas
8.1.1 National Institute of Standards and Technology
contaminated with radioactive waste.
(NIST) calibration and standardization procedures do not exist
8.4.1 Dead time corrections are usually negligible under
for gamma logging.
typical logging conditions when measured gamma counts are
8.1.2 Gammalogscanbeusedinaqualitative(for example,
less than a few hundred counts per second.
comparative) or quantitative (for example, estimating radioiso-
8.4.2 Dead time corrections are estimated by comparing the
tope concentration) manner depending upon the project objec-
gamma log response under the influence of two similar
tives.
radioactive sources. The measured count rate would approxi-
8.1.3 Gamma calibration and standardization methods and
mately double over that with one source when both sources are
frequency shall be sufficient to meet project objectives.
placedinthesamplevolumeoftheloggingtool.Thedeadtime
8.1.3.1 Calibrationandstandardizationshouldbeperformed
causesthecountratestobeslightlylessthandouble.Deadtime
eac
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.