IEC 61874:2025

IEC 61874 ®
Edition 2.0 2025-12
INTERNATIONAL
STANDARD
Nuclear instrumentation - Geophysical borehole instrumentation to determine
rock density ('density logging')

ICS 17.240  ISBN 978-2-8327-0844-6

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CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Equipment . 7
4.1 General . 7
4.2 Logging probe . 8
4.2.1 General. 8
4.2.2 Density eccentric device . 8
4.2.3 Gamma ray source . 8
4.2.4 Gamma ray detector . 8
4.2.5 Shielding and collimator. 8
4.3 Hoisting system and depth measuring system . 8
4.3.1 Hoisting system . 8
4.3.2 Depth measuring system . 8
4.4 Surface assembly . 9
4.4.1 General. 9
4.4.2 Data acquisition . 9
4.4.3 Data display . 9
4.4.4 Power assembly . 9
5 General requirements. 9
5.1 Design requirements . 9
5.2 Operational requirements . 10
5.2.1 General. 10
5.2.2 Time constant . 10
τ
5.2.3 Logging speed . 10
6 Mechanical and environmental performance requirements . 10
7 Measurement errors . 11
8 Operating time requirements . 11
9 Power supply requirements . 12
10 Mechanical and environmental performance tests . 12
10.1 Temperature and pressure test . 12
10.2 Vibration test . 12
10.3 Continuous running time test . 13
11 Functional tests . 13
11.1 Calibration . 13
11.2 Pre- and post-logging operation checks . 13
11.2.1 Pre-logging checks. 13
11.2.2 Post-logging checks . 13
12 Safety requirements . 14
12.1 Electrical safety requirements . 14
12.2 Radiation safety requirements . 14
13 Characteristics to be specified in the operation and maintenance documentation
or certificate of the equipment . 14

Table 1 – Operating and test conditions . 10
Table 2 – Environmental conditions for surface assembly . 11

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Nuclear instrumentation -
Geophysical borehole instrumentation to determine rock density ("density
logging")
FOREWORD
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
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IEC 61874 has been prepared by IEC technical committee 45: Nuclear instrumentation. It is an
International Standard.
This second edition cancels and replaces the first edition published in 1998. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Clause 2: updating of reference documents;
b) Clause 3: revision of the terms and definitions;
c) Clause 4: revision of the composition of the equipment;
d) Subclause 5.1.2: addition of the outside diameters of borehole probes;
e) Subclause 5.2.1: revision of the time constant;
f) Subclauses 6.1, 6.2, 6.3, and 6.6: revision of the mechanical and environmental
performance requirements;
g) Subclause 8.2: revision of the operating time requirements;
h) Clause 10: addition of the mechanical and environmental performance test methods;
i) Subclause 11.2: addition of the pre- and post-logging operation checks;
j) Clause 12: revision of the safety requirements;
k) Clause 13: addition of the characteristics to be specified in the operation and maintenance
documentation or certificate of the equipment.
The text of this International Standard is based on the following documents:
Draft Report on voting
45/1004/CDV 45/1014/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
1 Scope
This document applies to equipment consisting of:
– a borehole logging probe equipped with a collimated radioisotope (gamma) source (during
the actual measurements only) and a detector unit to measure scattered gamma radiation;
– a hoisting system and depth measuring system;
– other instruments and devices (power supply, pulse converter/amplifier, ratemeter, recorder,
signal processing and readout units).
This document defines the terminology, specifies the types of apparatus, design and general
technical requirements, specific radiation performance, electrical, mechanical, safe and
environmental performance requirements. It also defines test and calibration procedures and
covers electrical safety and radiation protection issues. Further, it gives recommendations
about items included in the manufacturer's operation and maintenance documentation (or
certificate).
The purpose of this document is to specify design requirements and performance
characteristics of nuclear instrumentation used in boreholes to determine bulk rock density in
situ. With suitable response charts the measurements can be equated to rock lithology and
porosity.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60050-395, International Electrotechnical Vocabulary (IEV) - Part 395: Nuclear
instrumentation - Physical phenomena, basic concepts, instruments, systems, equipment and
detectors
IEC 60359, Electrical and electronic measurement equipment - Expression of performance
IEC 61010-1, Safety requirements for electrical equipment for measurement, control, and
laboratory use - Part 1: General requirements
ISO 2919, Radiological protection - Sealed radioactive sources - General requirements and
classification
IAEA Safety Standards Series No.SSG-57, Radiation Safety in Well Logging
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-395,
IEC 60359 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://www.iso.org/obp
3.1
density logging
irradiation of the rock formations surrounding the borehole with a constant flux of medium
energy gamma rays from a sealed radioisotope source and counting the number and energy of
scattered gamma rays that reach detectors positioned at different distances
Note 1 to entry: The measurements are carried out by moving the source-detector assembly (i.e. logging probe)
along the borehole wall.
Note 2 to entry: Density logging generally includes single-detector density logging, compensated density logging
and litho-density logging.
Note 3 to entry: Single-detector density logging means that there is only one detector in the density logging.
Note 4 to entry: Compensated density logging means that there are two or more detectors in the density logging.
The data from two or more detectors can compensate for the influence of mud, mud cake and other wellbore
environmental factors on density measurements.
Note 5 to entry: Litho-density logging is an improvement and extension of density logging. In addition to recording
the density of the rock, it also measures the photoelectric absorption cross section index Pe of the formation, and
Pe is related to the lithology. During logging, the lower energy and higher energy parts of scattered gamma rays are
recorded by downhole instruments. The intensity of scattered gamma rays in the high-energy part depends on the
density; the low energy part is mainly related to lithology, but also related to density, and Pe can be obtained after
treatment.
3.2
working range
range of bulk density of rocks in which the measurements are carried out with specified
accuracy
3.3
rated operating conditions
set of working range operating characteristics for all influence quantities within which the
instrument specified errors are maintained
3.4
rated operating range
whole of working ranges for quantities to be measured within which the performance of the
apparatus is specified
3.5
basic error
error determined under test conditions
3.6
test conditions
set of influence quantity values and parameters with specified variation limits at which the
calibration is carried out
3.7
operating error
error of a performance characteristic which is obtained at any point within the rated operating
conditions
3.8
intrinsic error
error of a measuring instrume
...