ASTM D6726-01
(Guide)Standard Guide for Conducting Borehole Geophysical Logging-Electromagnetic Induction
Standard Guide for Conducting Borehole Geophysical Logging-Electromagnetic Induction
SCOPE
1.1 This guide is focused on the general procedures necessary to conduct electromagnetic-induction, induction, electromagnetic-conductivity, or electromagnetic-resistivity logging (hereafter referred as induction logging) of boreholes, wells, access tubes, caissons, or shafts (hereafter referred as boreholes) as commonly applied to geologic, engineering, ground-water and environmental (hereafter referred as geotechnical) investigations. Induction logging for minerals or petroleum applications is excluded.
1.2 This guide defines an induction log as a record of formation electrical conductivity or resistivity with depth as measured by the induction method in a borehole.
1.2.1 Induction logs are treated quantitatively and should be interpreted with other logs and data whenever possible.
1.2.2 Induction logs are commonly used to: ( 1) delineate lithology; (2) evaluate formation water quality and effective porosity, and (3) correlate stratigraphy between boreholes.
1.3 This guide is restricted to induction measurements that are at a frequency of less than 50 KHz; are non-directional; and average formation properties around the circumference of the borehole; which are the most common induction measurement devices used in geotechnical applications.
1.4 This guide provides an overview of induction logging including (1) general procedures; ( 2) specific documentation; (3) calibration and standardization; and (4) log quality and interpretation.
1.5 To obtain additional information on induction logs see References section in this guide.
1.6 This guide is to be used in conjunction with Standard Guide D 5753.
1.7 This guide offers an organized collection of information or a series of options and does not recommend a specific course of action. This guide should not be used as a sole criterion for induction logging and does not replace education, experience, and professional judgement. Induction logging procedures should be adapted to meet the needs of a range of applications and stated in general terms so that flexibility or innovation are not suppressed. 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 without consideration of a project's many unique aspects. The word standard in the title of this document means that the document has been approved through the ASTM consensus process.
1.8 The geotechnical industry uses English or SI units. The induction log is typically recorded in millisiemens per meter (mS/m) or millimhos per meter (mmhos/m).
1.9 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 requirements prior to use.
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: D 6726 – 01
Standard Guide for
Conducting Borehole Geophysical Logging—
Electromagnetic Induction
This standard is issued under the fixed designation D 6726; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope not suppressed. Not all aspects of this guide may be applicable
in all circumstances. This ASTM standard is not intended to
1.1 This guide is focused on the general procedures neces-
representorreplacethestandardofcarebywhichtheadequacy
sary to conduct electromagnetic-induction, induction,
of a given professional service must be judged without
electromagnetic-conductivity, or electromagnetic-resistivity
consideration of a project’s many unique aspects. The word
logging (hereafter referred as induction logging) of boreholes,
standard in the title of this document means that the document
wells, access tubes, caissons, or shafts (hereafter referred as
has been approved through the ASTM consensus process.
boreholes) as commonly applied to geologic, engineering,
1.8 The geotechnical industry uses English or SI units. The
ground-water and environmental (hereafter referred as geo-
induction log is typically recorded in millisiemens per meter
technical) investigations. Induction logging for minerals or
(mS/m) or millimhos per meter (mmhos/m).
petroleum applications is excluded.
1.9 This standard does not purport to address all of the
1.2 This guide defines an induction log as a record of
safety concerns, if any, associated with its use. It is the
formation electrical conductivity or resistivity with depth as
responsibility of the user of this standard to establish appro-
measured by the induction method in a borehole.
priate safety and health practices and determine the applica-
1.2.1 Induction logs are treated quantitatively and should be
bility of regulatory requirements prior to use.
interpreted with other logs and data whenever possible.
1.2.2 Induction logs are commonly used to: (1) delineate
2. Referenced Documents
lithology; (2) evaluate formation water quality and effective
2.1 ASTM Standards:
porosity, and (3) correlate stratigraphy between boreholes.
D 420 Guide to Site Characterization for Engineering, De-
1.3 This guide is restricted to induction measurements that
sign, and Construction Purposes
areatafrequencyoflessthan50KHz;arenon-directional;and
D 653 Terminology Relating to Soil, Rock and Contained
average formation properties around the circumference of the
Fluids
borehole; which are the most common induction measurement
D 5088 Practice for Decontamination of Field Equipment at
devices used in geotechnical applications.
Non- Radioactive Waste Sites
1.4 This guide provides an overview of induction logging
D 5608 Practice for Decontamination of Field Equipment
including (1) general procedures; (2) specific documentation;
Used at Low Level Radioactive Waste Sites
(3) calibration and standardization; and (4) log quality and
D 5730 Guide for Site Characterization for Environmental
interpretation.
Purposes with Emphasis on Soil, Rock, Vadose Zone, and
1.5 To obtain additional information on induction logs see
Ground Water
References section in this guide.
D 5753 Guide for Planning and Conducting Borehole Geo-
1.6 This guide is to be used in conjunction with Standard
physical Logging
Guide D 5753.
D 6167 Guide for Conducting Borehole Geophysical
1.7 This guide offers an organized collection of information
Logging—Mechanical Caliper
oraseriesofoptionsanddoesnotrecommendaspecificcourse
D 6235 Practice for Expediated Site Characterization of
of action. This guide should not be used as a sole criterion for
Vadose Zone and Ground Water Contamination of Haz-
induction logging and does not replace education, experience,
ardous Waste Contaminated Sites
and professional judgement. Induction logging procedures
D 6274 Guide for Conducting Borehole Geophysical
should be adapted to meet the needs of a range of applications
Logging—Gamma
and stated in general terms so that flexibility or innovation are
D 6429 Guide for Selecting Surface Geophysical Methods
D 6431 Guide for Using the Direct Current Resistivity
This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rock
and is the direct responsibility of Subcommittee D18.01 on Surface and Subsurface
Characterization. Annual Book of ASTM Standards, Vol 04.08.
Current edition approved Nov. 10, 2001. Published March 2002. Annual Book of ASTM Standards, Vol 04.09.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 6726
Method for Subsurface Investigations 6.3.1 Induction probes need to warm up and stabilize with
the borehole environment. Some probes record internal elec-
3. Terminology tronic temperature; this temperature record should not be
confused with a borehole fluid temperature log.
3.1 Definitions—Definitions shall be in accordance with
6.4 Effects of borehole fluid is dependent on probe design,
terms and symbols given in Terminology D 653.
borehole diameter, and borehole-fluid conductivity. Induction
3.2 Definitions of Terms Specific to This Standard:
measurements can be made in air-, water-, or mud-filled
3.2.1 accuracy—how close a measured log value ap-
boreholes.Inductionprobesaredesignedtominimizeeffectsof
proaches true value. It is determined in a controlled environ-
borehole fluid. Conductivity of borehole fluid will significantly
ment. A controlled environment represents a homogeneous
affect induction response only in larger diameter boreholes
sample volume with known properties.
(typically, greater than 8 to 10 in. (20 to 25 cm) diameter).
3.2.2 depth of investigation—the radial distance from the
6.4.1 Effects of mud-invasion zone is dependent on probe
measurement point to a point where the predominant measured
design, invasion depth, and mud and formation conductivity.
response may be considered centered, which is not to be
6.4.2 Steel or other conductive material interferes and may
confused with borehole depth (for example, distance) mea-
prohibit induction measurements. PVC casing and other non-
sured from the surface.
conductive casing does not affect induction response. Clay
3.2.3 measurement resolution—the minimum change in
seals and sand/gravel packs may affect induction response in
measured value that can be detected.
largerdiameterboreholes(typically,greaterthan8to10in.(20
3.2.4 repeatability—the difference in magnitude of two
to 25 cm) diameter).
measurements with the same equipment and in the same
6.5 Geologic Conditions:
environment.
6.5.1 In high-conductivity formations and ground water, the
3.2.5 vertical resolution—the minimum thickness that can
electrical conductivity measured by induction is less than the
be separated into distinct units.
true electrical conductivity due to skin effects. Some probes
3.2.6 volume of investigation—the volume that contributes
correct for skin effect assuming a homogeneous medium.
90 percent of the measured response. It is determined by a
6.5.2 In steeply dipping formations (greater than 60 de-
combination of theoretical and empirical modeling. The vol-
grees), electrical anisotropy affects apparent bed thickness and
ume of investigation is non-spherical and has gradational
location of bed contacts and corrections need to be applied.
boundaries.
6.6 Theoretical and empirical tool response curves and
inversion algorithms may be applied to correct for many
4. Summary of Guide
interferences.
4.1 This guide applies to induction logging and is to be use
in conjunction with Guide D 5753.
7. Apparatus
4.2 This guide briefly describes the significance and use,
7.1 Ageophysical logging system has been described in the
apparatus, calibration and standardization, procedures and
general guide (Section 6, Guide D 5753).
reports for conducting induction logging.
7.2 Induction logs are collected with probes that have
electromagnetic transmitter and receiver coils (Fig. 1).
5. Significance and Use
7.2.1 Transmitter and receiver coils typically are spaced
5.1 An appropriately developed, documented, and executed
about 20 in. (50 cm) apart. In deep-induction configurations,
guide is essential for the proper collection and application of
coils are spaced at about 40 in (1 m) apart.
induction logs. This guide is to be used in conjunction with
7.2.2 The transmitter coil emits an electromagnetic signal in
Guide D 5753.
the range of 20 to 40 KHz that induces eddy currents in the
5.2 The benefits of its use include improving: selection of
medium surrounding the borehole.
induction logging methods and equipment; induction log
7.2.3 The receiver coil senses the primary and secondary
quality and reliability; and usefulness of the induction log data
magnetic fields.
for subsequent display and interpretation.
7.2.4 Strength of the secondary magnetic field is a function
5.3 This guide applies to commonly used induction logging
of the electrical conductivity of the surrounding medium.
methods for geotechnical applications.
7.2.5 One or more additional coils are used to cancel the
5.4 It is essential that personnel (see Section 8.3.2, Guide
primaryfield,reducesensitivitytotheboreholefluid,andfocus
D 5753) consult up-to-date textbooks and reports on the
the horizontal response.
induction technique, application, and interpretation methods.
7.3 Volume of Investigation and Depth of Investigation of
induction measurements are dependent on coil configuration
6. Interferences
and increases with increased spacing between transmitter and
6.1 Most extraneous effects on induction logs are caused by receiver coils.
logging procedures, instrument problems, borehole conditions, 7.3.1 The Depth of Investigation typically varies from 20 to
and geologic conditions. 30 in. (50 to 75 cm) (Fig. 2), but is up to 130 in. (325 cm) in
6.2 Logging procedures include incorrect range setting, deep-induction configurations.
incorrect calibration, and logging too fast. 7.3.2 The radial distance from which log response is negli-
6.3 Instrument problems include electrical leakage and tem- gible typically varies from 3 to 5 in. (7.5 to 12.5 cm), but is 20
perature drift. in. (50 cm) or more in deep-induction configurations.
D 6726
FIG. 1 Electromagnetic-Induction Logging System (8)
FIG. 2 Cumulative Response Versus Radial Distance for a Typical Electromagnetic-Induction Probe Showing Depth of Investigation and
Radial Focusing (11)
7.3.3 Induction probes used for geotechnical applications 7.6.2 Induction and gamma logs can be collected in open or
typically can be logged inside of a 2 in. (5 cm) diameter boreholes cased with non-conductive materials (PVC, fiber-
monitoring well. glass, etc.) that are air, water, or mud filled.
7.3.4 Dual-induction probes have coil configurations that 7.6.3 Some induction probes may also record magnetic
measure two different depths of investigations including deep susceptibility simultaneously with the electric conductivity
induction and generally are greater than 2 in. (5 cm) in measurement. Note induction probes typically are not opti-
diameter. mized for magnetic susceptibility measurements.
7.4 VerticalResolutionofinductionmeasurementsisdepen- 7.7 Measurement resolution of induction probes is deter-
dent on coil configuration. mined by probe design. Measurement resolution is typically
7.4.1 Vertical Resolution is approximated by dividing the 0.01 mS/m.
transmitter-receiver coil spacing by 1.5. 7.8 A variety of induction logging equipment available is
7.4.2 Vertical Resolution typically is about 14 in. (35 cm). for geotechnical investigations. It is not practical to list all of
7.4.3 Vertical Resolution is up to 6 feet in deep-induction the sources of potentially acceptable equipment.
configurations.
8. Calibration and Standardization of Electromagnetic-
7.5 Typical accuracy is within 5 percent at 30 mS/m.
Induction Logs
7.6 Additional logs may also be run in combination with
induction. 8.1 General:
7.6.1 Induction probes commonly have the capability to 8.1.1 National Institute of Standards and Technology
simultaneously record gamma along with electrical conductiv- (NIST) calibration and standardization procedures do not exist
ity. for induction logging.
D 6726
8.1.2 Induction logs can be used in a qualitative (for 9.2 Identify induction-logging objectives.
example, comparative) or quantitative manner depending upon
9.3 Select appropriate equipment to meet objectives.
the project objectives.
9.3.1 Induction logs are commonly run with gamma logs to
8.1.3 Induction calibration methods and frequency shall be
aid in lithologic and water-quality interpretations. Although
sufficient to meet project objectives.
less commonly run, neutron logs also aid interpretations.
8.1.3.1 Calibrationandstandardizationshouldbeperformed
9.3.2 Combination induction and gamma probes commonly
each time an induction probe is suspected to be damaged,
have the induction transmitter and receiver in the lower part
modified, repaired, and at periodic intervals.
and the gamma detector in the upper part. This may be
8.1.3.2 Induction probe calibration is sensitive to the effects
inappropriate for shallow boreholes and induction and gamma
oftemperature,humidity,calibrationcoilposition,andconduc-
may have to be run separate to meet project objectives.
tive material.
9.3.3 Induction probes typically are run free-hanging where
8.2 Calibration is the process of establishing values for
the probes lies against one side of the borehole. Centralizers
induction response and is accomplished in free air and with
constructed of plastic or other non-conductive material are
representative physical models. Calibration data values related
sometimes used in boreholes 6 in. (15 cm) diameter or greater.
to the physical properties are recorded in units (for example,
Induction response may be somewhat different depending on
counts per second) that are converted to units of electrical
the method used (for example, free-hanging or centralized).
conductivity (mS/m).
9.3.4 Induction-probe and cable decontamination is ad-
8.2.1 At least two, and preferably more, values, which
dressed according to project specifications (see Practice
approximate the anticipated operating range, are needed to
D 5088 for non-radioactive waste sites and Practice D 5608 for
establish a calibration curve (for example, 10 and 100 mS/m).
low-level radioactive waste sites).
8.2.2 Typical tolerances for calibration are 5 percent of
9.4 Selectwh
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.