ASTM D6726-01(2007)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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: D6726 − 01(Reapproved 2007)
Standard Guide for
Conducting Borehole Geophysical Logging—
Electromagnetic Induction
This standard is issued under the fixed designation D6726; 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 induction logging and does not replace education, experience,
and professional judgement. Induction logging procedures
1.1 This guide is focused on the general procedures neces-
should be adapted to meet the needs of a range of applications
sary to conduct electromagnetic-induction, induction,
and stated in general terms so that flexibility or innovation are
electromagnetic-conductivity, or electromagnetic-resistivity
not suppressed. Not all aspects of this guide may be applicable
logging (hereafter referred as induction logging) of boreholes,
in all circumstances. This ASTM standard is not intended to
wells, access tubes, caissons, or shafts (hereafter referred as
representorreplacethestandardofcarebywhichtheadequacy
boreholes) as commonly applied to geologic, engineering,
of a given professional service must be judged without
groundwater and environmental (hereafter referred as geotech-
consideration of a project’s many unique aspects. The word
nical) investigations. Induction logging for minerals or petro-
standard in the title of this document means that the document
leum applications is excluded.
has been approved through the ASTM consensus process.
1.2 This guide defines an induction log as a record of
1.8 The geotechnical industry uses English or SI units. The
formation electrical conductivity or resistivity with depth as
induction log is typically recorded in millisiemens per meter
measured by the induction method in a borehole.
(mS/m) or millimhos per meter (mmhos/m).
1.2.1 Induction logs are treated quantitatively and should be
1.9 This standard does not purport to address all of the
interpreted with other logs and data whenever possible.
safety concerns, if any, associated with its use. It is the
1.2.2 Induction logs are commonly used to: (1) delineate
responsibility of the user of this standard to establish appro-
lithology; (2) evaluate formation water quality and effective
priate safety and health practices and determine the applica-
porosity, and (3) correlate stratigraphy between boreholes.
bility of regulatory requirements prior to use.
1.3 This guide is restricted to induction measurements that
areatafrequencyoflessthan50KHz;arenon-directional;and
2. Referenced Documents
average formation properties around the circumference of the
2.1 ASTM Standards:
borehole; which are the most common induction measurement
D420 Guide to Site Characterization for Engineering Design
devices used in geotechnical applications.
and Construction Purposes (Withdrawn 2011)
1.4 This guide provides an overview of induction logging
D653 Terminology Relating to Soil, Rock, and Contained
including (1) general procedures; (2) specific documentation;
Fluids
(3 ) calibration and standardization; and (4) log quality and
D5088 Practice for Decontamination of Field Equipment
interpretation.
Used at Waste Sites
1.5 To obtain additional information on induction logs see
D5608 Practices for Decontamination of Field Equipment
References section in this guide.
Used at Low Level Radioactive Waste Sites
D5730 Guide for Site Characterization for Environmental
1.6 This guide is to be used in conjunction with Standard
Purposes With Emphasis on Soil, Rock, the Vadose Zone
Guide D5753.
and Groundwater (Withdrawn 2013)
1.7 This guide offers an organized collection of information
D5753 Guide for Planning and Conducting Borehole Geo-
oraseriesofoptionsanddoesnotrecommendaspecificcourse
physical Logging
of action. This guide should not be used as a sole criterion for
1 2
This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rock For referenced ASTM standards, visit the ASTM website, www.astm.org, or
and is the direct responsibility of Subcommittee D18.01 on Surface and Subsurface contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Characterization. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved July 1, 2007. Published August 2007. Originally the ASTM website.
approved in 2001. Last previous edition approved in 2001 as D6727 – 01. DOI: The last approved version of this historical standard is referenced on
10.1520/D6726-01R07. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6726 − 01 (2007)
D6167 Guide for Conducting Borehole Geophysical Log- 5.4 It is essential that personnel (see Section 8.3.2, Guide
ging: Mechanical Caliper D5753) consult up-to-date textbooks and reports on the induc-
D6235 Practice for Expedited Site Characterization of Va- tion technique, application, and interpretation methods.
dose Zone and Groundwater Contamination at Hazardous
Waste Contaminated Sites
6. Interferences
D6274 Guide for Conducting Borehole Geophysical Log-
6.1 Most extraneous effects on induction logs are caused by
ging - Gamma
logging procedures, instrument problems, borehole conditions,
D6429 Guide for Selecting Surface Geophysical Methods
and geologic conditions.
D6431 Guide for Using the Direct Current Resistivity
6.2 Logging procedures include incorrect range setting,
Method for Subsurface Investigation
incorrect calibration, and logging too fast.
3. Terminology 6.3 Instrument problems include electrical leakage and tem-
perature drift.
3.1 Definitions—Definitions shall be in accordance with
6.3.1 Induction probes need to warm up and stabilize with
terms and symbols given in Terminology D653.
the borehole environment. Some probes record internal elec-
3.2 Definitions of Terms Specific to This Standard:
tronic temperature; this temperature record should not be
3.2.1 accuracy—how close a measured log value ap-
confused with a borehole fluid temperature log.
proaches true value. It is determined in a controlled environ-
6.4 Effects of borehole fluid is dependent on probe design,
ment. A controlled environment represents a homogeneous
borehole diameter, and borehole-fluid conductivity. Induction
sample volume with known properties.
measurements can be made in air-, water-, or mud-filled
3.2.2 depth of investigation—the radial distance from the
boreholes.Inductionprobesaredesignedtominimizeeffectsof
measurement point to a point where the predominant measured
borehole fluid. Conductivity of borehole fluid will significantly
response may be considered centered, which is not to be
affect induction response only in larger diameter boreholes
confused with borehole depth (for example, distance) mea-
(typically, greater than 8 to 10 in. (20 to 25 cm) diameter).
sured from the surface.
6.4.1 Effects of mud-invasion zone is dependent on probe
3.2.3 measurement resolution—the minimum change in
design, invasion depth, and mud and formation conductivity.
measured value that can be detected.
6.4.2 Steel or other conductive material interferes and may
prohibit induction measurements. PVC casing and other non-
3.2.4 repeatability—the difference in magnitude of two
conductive casing does not affect induction response. Clay
measurements with the same equipment and in the same
seals and sand/gravel packs may affect induction response in
environment.
largerdiameterboreholes(typically,greaterthan8to10in.(20
3.2.5 vertical resolution—the minimum thickness that can
to 25 cm) diameter).
be separated into distinct units.
6.5 Geologic Conditions:
3.2.6 volume of investigation—the volume that contributes
6.5.1 In high-conductivity formations and groundwater, the
90 percent of the measured response. It is determined by a
electrical conductivity measured by induction is less than the
combination of theoretical and empirical modeling. The vol-
true electrical conductivity due to skin effects. Some probes
ume of investigation is non-spherical and has gradational
correct for skin effect assuming a homogeneous medium.
boundaries.
6.5.2 In steeply dipping formations (greater than 60
degrees), electrical anisotropy affects apparent bed thickness
4. Summary of Guide
andlocationofbedcontactsandcorrectionsneedtobeapplied.
4.1 This guide applies to induction logging and is to be use
6.6 Theoretical and empirical tool response curves and
in conjunction with Guide D5753.
inversion algorithms may be applied to correct for many
4.2 This guide briefly describes the significance and use,
interferences.
apparatus, calibration and standardization, procedures and
reports for conducting induction logging.
7. Apparatus
7.1 Ageophysical logging system has been described in the
5. Significance and Use
general guide (Section 6, Guide D5753).
5.1 An appropriately developed, documented, and executed
7.2 Induction logs are collected with probes that have
guide is essential for the proper collection and application of
electromagnetic transmitter and receiver coils (Fig. 1).
induction logs. This guide is to be used in conjunction with
7.2.1 Transmitter and receiver coils typically are spaced
Guide D5753.
about 20 in. (50 cm) apart. In deep-induction configurations,
5.2 The benefits of its use include improving: selection of
coils are spaced at about 40 in (1 m) apart.
induction logging methods and equipment; induction log
7.2.2 The transmitter coil emits an electromagnetic signal in
quality and reliability; and usefulness of the induction log data
the range of 20 to 40 KHz that induces eddy currents in the
for subsequent display and interpretation.
medium surrounding the borehole.
5.3 This guide applies to commonly used induction logging 7.2.3 The receiver coil senses the primary and secondary
methods for geotechnical applications. magnetic fields.
D6726 − 01 (2007)
FIG. 1 Electromagnetic-Induction Logging System (1)
7.2.4 Strength of the secondary magnetic field is a function 7.3.4 Dual-induction probes have coil configurations that
of the electrical conductivity of the surrounding medium. measure two different depths of investigations including deep
7.2.5 One or more additional coils are used to cancel the induction and generally are greater than 2 in. (5 cm) in
primaryfield,reducesensitivitytotheboreholefluid,andfocus diameter.
the horizontal response.
7.4 VerticalResolutionofinductionmeasurementsisdepen-
7.3 Volume of Investigation and Depth of Investigation of
dent on coil configuration.
induction measurements are dependent on coil configuration
7.4.1 Vertical Resolution is approximated by dividing the
and increases with increased spacing between transmitter and
transmitter-receiver coil spacing by 1.5.
receiver coils.
7.4.2 Vertical Resolution typically is about 14 in. (35 cm).
7.3.1 The Depth of Investigation typically varies from 20 to
7.4.3 Vertical Resolution is up to 6 feet in deep-induction
30 in. (50 to 75 cm) (Fig. 2), but is up to 130 in. (325 cm) in
configurations.
deep-induction configurations.
7.5 Typical accuracy is within 5 percent at 30 mS/m.
7.3.2 The radial distance from which log response is negli-
7.6 Additional logs may also be run in combination with
gible typically varies from 3 to 5 in. (7.5 to 12.5 cm), but is 20
in. (50 cm) or more in deep-induction configurations. induction.
7.3.3 Induction probes used for geotechnical applications 7.6.1 Induction probes commonly have the capability to
typically can be logged inside of a 2 in. (5 cm) diameter simultaneously record gamma along with electrical conductiv-
monitoring well. ity.
FIG. 2 Cumulative Response Versus Radial Distance for a Typical Electromagnetic-Induction Probe Showing Depth of Investigation and
Radial Focusing (2)
D6726 − 01 (2007)
7.6.2 Induction and gamma logs can be collected in open or 8.2.6 Calibration also can be established in a body of water
boreholes cased with non-conductive materials (PVC, such as a lake with a known electrical conductivity that is large
fiberglass, etc.) that are air, water, or mud filled. enough to be infinite with respect of the Volume of Investiga-
7.6.3 Some induction probes may also record magnetic tion of the probe.
susceptibility simultaneously with the electric conductivity
8.2.7 Calibration should be performed when the probe
measurement. Note induction probes typically are not opti-
temperature is as close to the borehole temperature as possible.
mized for magnetic susceptibility measurements.
This is most readily performed by recalibrating immediately
after logging a borehole.
7.7 Measurement resolution of induction probes is deter-
mined by probe design. Measurement resolution is typically
8.3 Standardization is the process of checking logging
0.01 mS/m.
response to show evidence of repeatability and consistency.
8.3.1 Calibration insures standardization.
7.8 A variety of induction logging equipment available is
8.3.2 Arepresentative borehole may be used to periodically
for geotechnical investigations. It is not practical to list all of
check induction probe response providing the borehole and
the sources of potentially acceptable equipment.
surroundingenvironmentdoesnotchangewithtimeorchanges
and their effects on induction response can be documented.
8. Calibration and Standardization of Electromagnetic-
Induction Logs
9. Procedure
8.1 General:
9.1 See Section 8, Guide D5753 for planning a logging
8.1.1 National Institute of Standards and Technology
program, data formats, personnel qualifications, field
(NIST) calibration and standardization procedures do not exist
documentation, and header documentation.
for induction logging.
9.1.1 Induction specific information (for example, coil
8.1.2 Induction logs can be used in a qualitative (for
example, comparative) or quantitative manner depending upon spacing, transmitter frequency) should be documented.
the project objectives.
9.2 Identify induction-logging objectives.
8.1.3 Induction calibration methods and frequency shall be
9.3 Select appropriate equipment to meet objectives.
sufficient to meet project objectives.
9.3.1 Induction logs are commonly run with gamma logs to
8.1.3.1 Calibrationandstandardizationshouldbeperformed
aid in lithologic and water-quality interpretations. Although
each time an induction probe is suspected to be damaged,
less commonly run, neutron logs also aid interpretations.
modified, repaired, and at periodic intervals.
9.3.2 Combination induction and gamma probes commonly
8.1.3.2 Induction probe calibration is sensitive to the effects
ha
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