ISO/TR 14685:2001

TECHNICAL ISO/TR
REPORT 14685
First edition
2001-12-15
Hydrometric determinations — Geophysical
logging of boreholes for hydrogeological
purposes — Considerations and guidelines
for making measurements
Déterminations hydrométriques — Répertoriage géophysique des trous de
sonde pour des besoins hydrogéologiques — Considérations et lignes
directrices relatives aux mesurages

Reference number
©
ISO 2001
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ii © ISO 2001 – All rights reserved

Contents Page
Foreword.iv
Introduction.v
1 Scope .1
2 Terms and definitions .1
3 Units of measurement.6
4 Purpose of geophysical logging .6
4.1 General.6
4.2 Formation logging .7
4.3 Fluid logging .9
4.4 Construction logging .12
4.5 Selection of logs .12
5 Planning.13
5.1 General considerations.13
5.2 Safety around wells, boreholes and shafts .15
5.3 Site access .15
5.4 Access within a borehole.16
5.5 Equipment .16
5.6 Borehole details.16
5.7 Logging sequence .17
5.8 Quality assurance.18
6 Formation logging .18
6.1 General.18
6.2 Electric logs .18
6.3 Natural gamma-ray logs.21
6.4 Neutron-neutron (porosity) logs .22
6.5 Gamma-gamma (density) logs .23
6.6 Sonic logs.24
6.7 Other logs.25
7 Fluid logging .26
7.1 General.26
7.2 Temperature .26
7.3 Fluid conductivity.26
7.4 Flow.28
8 Construction logging .29
8.1 General.29
8.2 Calliper.29
8.3 Casing collar locator .30
8.4 Cement bond.31
8.5 Closed circuit television log.32
9 Log presentation.32
9.1 General.32
9.2 Track layout.35
9.3 Log parameter scales.35
9.4 Depth scales.35
9.5 Composite logs.35
9.6 Differential logs.36
Bibliography.37
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
The main task of technical committees is to prepare International Standards. Draft International Standards adopted
by the technical committees are circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting a vote.
In exceptional circumstances, when a technical committee has collected data of a different kind from that which is
normally published as an International Standard (“state of the art”, for example), it may decide by a simple majority
vote of its participating members to publish a Technical Report. A Technical Report is entirely informative in nature
and does not have to be reviewed until the data it provides are considered to be no longer valid or useful.
Attention is drawn to the possibility that some of the elements of this Technical Report may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO/TR 14685 was prepared by Technical Committee ISO/TC 113, Hydrometric determinations, Subcommittee
SC 8, Ground water.
iv © ISO 2001 – All rights reserved

Introduction
Geophysical logging of boreholes, wells and/or shafts (hereafter referred to as boreholes) for hydrogeologic
purposes provides a measurement of various physical and chemical properties of formations penetrated by a
borehole and of their contained fluids. Sondes measuring different parameters are lowered into the borehole and
the continuous depthwise change in a measured parameter is presented graphically as a geophysical log.
Geophysical logging of boreholes is carried out to obtain information on:
a) the lithology of the formations through which the borehole is drilled;
b) the occurrence, quantity, location and quality of formation fluid (usually water);
c) the dimensions, construction and physical condition of the borehole.
The logging equipment consists essentially of three parts: the downhole sensor and oblique tool (hereafter referred
to as a sonde); cable and winch; power and a surface system of power, signal processing and recording units (see
Figure 1).
The various sondes contain sensors to enable specific properties to be measured. Output from the sondes is in the
form of electronic signals, either analogue or digital. These signals are transmitted to the surface instruments via
the cable and winch.
The cable serves the dual purpose of supporting the sonde and conveying electrical power and signals to and from
the sonde. To this end it has a double outer layer of high tensile steel or polyurethane/kevlar.
The winch serves to raise or lower the sonde and to measure its precise depth. This is achieved by passing the
cable round a measuring sheave of known diameter linked to an accurate depth measuring system.
The surface instrumentation typically consists of two sections to provide power and process the electronic signals
from each of the sondes for recording purposes.
Data recorder units are either analogue or digital, comprising pen and ink recorders, film, a dedicated computer,
encoding the signal data from the sonde or surface modules, formatting them and storing them on magnetic tape or
disk, and driving the plotter to produce filed logs.
Key
1 Sensor 9 Recorder drive 17 ac power source (regulated)
2 Electronic section 10 Winch 18 Recorder
3 Cable head 11 Slip ring 19 Depth indicator
4 Sonde 12 Ground (electric logging) 20 Varying dc voltage (mV) for driving recorder pens
5 Power (down) 13 Motor 21 Logging speed and direction
6 Signal (up) 14 Signal 22 Downhole power (not universal)
7 Logging cable 15 Power 23 Signal conditioning; zero positioning; sensitivity; time
constant etc.
8 Cable-measuring sheave 16 Vertical scale control
24 Logging controls
NOTE Taken from reference [14].
Figure 1 — Schematic of a basic geophysical logging system
vi © ISO 2001 – All rights reserved

TECHNICAL REPORT ISO/TR 14685:2001(E)

Hydrometric determinations — Geophysical logging of boreholes
for hydrogeological purposes — Considerations and guidelines for
making measurements
1 Scope
This Technical Report is a summary of best practice for those involved in geophysical borehole logging for
hydrogeological purposes. It describes the factors that need to be considered and the measurements that are
required to be made when logging boreholes. There can, however, be no definite “standard” logging procedure
because of great diversity of objectives, groundwater conditions and available technology. Geophysical logging of
boreholes is an evolving science, continually adopting new and different techniques. Every application poses a
range of problems and is likely to require a particular set of logs to gain maximum information. This Technical
Report therefore provides information on field practice with the objective of how variations in measured parameters
may be useful to take account of particular local conditions. It deals with the usual types of logging carried out for
delineation of aquifer boundaries; mapping aquifer geometry; assessing the chemical quality and quantity of ground
water; water-supply purposes; landfill investigations and contamination studies; borehole construction and
conditions; and subsurface lithological information.
Applications not specifically considered in this Technical Report include mineral and hydrocarbon evaluation and
geotechnical and structural engineering investigations. However, this Technical Report may be a source of general
information for any borehole geophysical logging effort.
NOTE Interpretation of the data collected during logging is referred to in this Technical Report only in a general way. For
full details of the analysis and interpretation of geophysical logs, reference should be made to specialized texts. Examples of
such texts are included in the Bibliography.
2 Terms and definitions
For the purposes of this Technical Report, the following terms and definitions apply.
2.1
abstraction
removal of water from a borehole or well
2.2
access tube
dip tube
pipe inserted into a well to permit safe installation of instruments, thus safeguarding them from touching or
becoming entangled with the pump or other equipment in the well
2.3
air lifting
method of producing a discharge of water from a borehole by the injection of compressed air
2.4
aquifer
lithological unit, group of lithological units, or part of a lithological unit containing sufficient saturated permeable
material to yield significant quantities of water to wells, boreholes, or springs
2.5
aquifer properties
properties of an aquifer that determine its hydraulic behaviour and its response to abstraction
2.6
argillaceous
containing clay minerals
2.7
bed resolution
minimum bed thickness that can be resolved
2.8
bonding
seal between a borehole lining and the geological formation
2.9
cable boom
rigid support from which the geophysical sonde and cable are suspended
2.10
calibration tail
section of field log carrying information on sonde calibration
2.11
casing
tubular retaining structure, which is installed in a drilled borehole or excavated well, to maintain the borehole
opening
NOTE Plain casing prevents the entry of water.
2.12
casing string
set of lengths of casing assembled for lowering into a borehole
2.13
composite log
several well logs of the same or similar types suitable for correlation, spliced together to form a single continuous
record
2.14
core
section of geological formation obtained from a borehole by drilling
2.15
curve matching
comparison of individual borehole data in graphical form with standard or control data
2.16
drawdown
reduction in static head within the aquifer resulting from abstraction
2.17
drilling circulation
movement of drilling fluid (air foam or liquid) used to clear the borehole during drilling
2 © ISO 2001 – All rights reserved

2.18
filter pack
granular material introduced into a borehole between the aquifer and a screen or perforated lining to prevent or
control the movement of particles from the aquifer into the borehole
2.19
fishing tool
grappling equipment used to locate and recover items from within a borehole
2.20
flushed zone
zone at a relatively short radial distance from the borehole immediately behind the mudcake where all of the pore
spaces are filled with borehole fluid
2.21
fluid column
that part of a borehole filled with fluid
2.22
formation
geological unit or series of units
2.23
geophysical log
continuous record of a physical or chemical property plotted against depth or time
2.24
grain size
principal dimension of the basic particle making up an aquifer or lithological unit
2.25
grout
cement and water mixture
2.26
header information
description of type of data required for inclusion in a table or as input to a computer program
2.27
invaded zone
portion of formation surrounding a borehole into which drilling fluid has partially penetrated
2.28
jig
calibrating device for logging sondes
2.29
leachate
liquid that has percolated through solid wastes
2.30
lining
tube or wall used to support the sides of a well and sometimes to prevent the entry of water
2.31
lithology
physical character and mineralogical composition that gives rise to the appearance and properties of a rock or
sediment
2.32
logging
recording of data
2.33
mud cake
residue deposited on the borehole wall during drilling
2.34
open borehole
unlined borehole
2.35
packer
device placed in a borehole to seal or plug it at a specific point
2.36
permeability
characteristic of a material that determines the rate at which fluids pass through it under the influence of differential
pressure
2.37
photomultiplier
electronic device for amplifying and converting light pulses into measurable electrical signals
2.38
plummet
plumb bob used for determining the apparent depth of a borehole
2.39
porosity
ratio of the volume of pore space in a sample to the bulk volume of that sample
2.40
rising main
pipe carrying water from within a well to a point of discharge
2.41
rugosity
degree of roughness (of the borehole wall)
2.42
saline interface
boundary between waters of differing salt content
2.43
saturated zone
that part of earthen material normally beneath the water table in which all voids are filled with water that is under a
greater-than-atmospheric pressure
2.44
screen
type of lining tube, with apertures designed to permit the flow of water into a well while preventing the entry of
aquifer or filter pack material
2.45
sidewalling
running a log up or down a borehole with the sonde in contact with the borehole wall
4 © ISO 2001 – All rights reserved

2.46
sonde
cable-suspended probe or tool containing a sensor
2.47
unconfined aquifer
water bearing formation with a free water surface
2.48
unconsolidated rock
rock that lacks natural cementation
2.49
unsaturated zone
that part of earthen material between the land surface and the water table
2.50
washout
cavity formed by the action of drilling
2.51
water table
surface of the saturated zone at which the water pressure is atmospheric
2.52
API unit
American Petroleum Institute unit
unit or counting rate used for scaling gamma-ray logs and neutron logs
3 Units of measurement
Table 1 gives a list of parameters and units of measurement in common use. Historically there has been a mix of
units, many from the oil industry and the United States.
Table 1 — Parameters and units of measurement
Parameter Units of measurement Logging method
Electrical resistivity Ωm Resistivity
Electrical conductivity mS/m Induction
Electrical potential mV Spontaneous potential (SP)
Natural gamma radiation API units (see 2.52) Gamma-ray
Percent “matrix” porosity where matrix has to be
Porosity Neutron; gamma-gamma; sonic
stated as sandstone, limestone or dolomite porosity
Bulk density g/cm Gamma-gamma (Compton effect)
Acoustic velocity m/s Sonic
Fluid temperature °C Fluid temperature
Temperature gradient °C/m Differential temperature
Fluid conductivity µS/cm Fluid conductivity
Conductivity gradient S/m Differential conductivity
Flowmeter; heat pulse flowmeter; tracer pulse
Fluid velocity mm/s flowmeter; packer-flowmeter (PFM); repeated
fluid conductivity/temperature logging
Borehole diameter mm Calliper
Cement bonding % Sonic bond
Casing condition mV Casing collar location (CCL)

4 Purpose of geophysical logging
4.1 General
Ideally, every borehole drilled for hydrogeological purposes should be geophysically logged. For a small
percentage (typically 2 % to 10 %) of the cost of drilling a borehole, the return of information derived from
geophysical logs can far exceed that derived from drilling samples. Logging costs are an even smaller percentage
of total costs for developing a groundwater source or remediation of contamination. Even when a borehole is totally
cored and 100 % recovery is achieved, many geophysical logs will continuously sample many times (10 or more)
the volume of the cores.
Not only are coring and subsequent laboratory analysis very expensive, they are also time-consuming. Long-term
storage of cores presents problems but digital data of geophysical logs can be stored and recalled easily. Whilst
there can be no substitute for high quality lithological samples for determining strata classification, lithology, mineral
content and grain size, the geophysical log provides in situ data on the hydrogeological regime around the
borehole. Also, it provides correction for depth uncertainty of lag in sample collection.
Boreholes drilled for hydrogeological investigation are not often cored and good sample collection techniques are
often difficult to achieve. Sample quality is unpredictable in these circumstances and sampling will not be possible
where drilling circulation is lost. It is in such situations that geophysical logging provides a continuous quantitative
set of data when compared with the drilling samples, which are always subjective. Furthermore geophysical logging
can be used in old boreholes where geological records are undocumented.
6 © ISO 2001 – All rights reserved

In addition to lithological interpretation, a number of physical and chemical properties of the surrounding rock and
fluids contained therein can be investigated.
Geophysical logs can be run in all boreholes including those cased with metal or plastic casing and filled with
water, brine, mud, drilling foam or air. The greatest return of information is derived from open (uncased) boreholes
filled with formation water or mud. In plain-cased boreholes, investigation of the geological formation is limited to
the nuclear logs and, with plastics casing, induction logs may also be used. Conventional resistivity logs (especially
focused ones) are possible to use in plastic screens.
The wealth of information from geophysical logs means that they can be used in many spheres of hydrogeological
investigation; for example, in water resources projects to investigate aquifer hydraulics and distribution of yield
within an aquifer of group of aquifers. In the rapidly expanding field of groundwater quality control, geophysical
logging is now extensively used to monitor groundwater pollution, to trace leachate movement and to monitor the
boundaries between saline interfaces.
Borehole logging is also important in investigating the deep hydraulic and hydrogeological properties of rocks in
geothermal and radioactive waste disposal projects. There are a number of engineering applications of geophysical
logging for investigating borehole conditions and, where television logging is available, for the inspection of casing
and pumps.
Figure 2 shows an example of a composite log where the disposition of aquifers can be seen.
Geophysical logging can be repeated many times in a borehole or series of boreholes at intervals ranging from
minutes to years, adding a new dimension to the information obtainable. This is particularly applicable to aquifer
hydraulics and recharge and pollution studies.
Geophysical logs also provide information that can be directly used in surface geophysical studies for
standardization and calibration of parameters. For example, sonic logs can be calibrated with seismic sections and
resistivity logs can be compared with surface electrical resistivity surveys for resistivity standardization.
4.2 Formation logging
4.2.1 General
No geophysical log has a unique response to a particular rock type or named stratigraphic unit and at some point in
any hydrogeological investigation the formation logs have to be referred to a borehole with a well-described set of
samples.
It is important therefore that formation logs should be run not just in boreholes where incomplete or no samples are
available but in all boreholes, particularly any which have been cored. The three main purposes of formation
logging are described in 4.2.2 to 4.2.4.
4.2.2 Identification of lithology
Geophysical logging can provide a very detailed description of subsurface formation lithologies. Some logs such as
the natural gamma log commonly provide an unambiguous delineation of shale and shale-free zones, with the SP
and electrical resistivity logs supplying supporting evidence. Other logs are generally not diagnostic on their own
but in combination can provide accurate information. The combination of calibrated neutron porosity and density
logs, for example, will differentiate sandstone, limestone and dolomite of different porosities. The additional
information provided by the sonic log enables the identification of halite, gypsum and other minerals.
Where calibrated logs are unavailable, differentiation of lithology will require some geological knowledge, this often
being obtained from examination of core samples or cuttings. Where core recovery is incomplete, geophysical logs
will normally provide a complete lithological description together with accurate depths to lithological boundaries.
The use of geophysical log interpretation is a major factor in the design of casing strings particularly in large
thicknesses of variable unconsolidated alluvial sediments. The positioning of plain and screen casing is commonly
based entirely on a natural gamma log run in a temporarily cased borehole.
Key
1 Poorly cemented very fine 7 Very fine sandstone and siltstone 13 Siltstone grading down into
sandstone and siltstone mudstone with anhydrite and halite
8 Halite veins in siltstone
veins and nodules
2 Anhydrite
9 Halite veins and nodules in very
14 Mudstone
3 Very fine sandstone fine sandstone and siltstone
15 Mudstone with halite veins
4 Very fine sandstone and siltstone 10 Halite cemented very fine
with anhydrite sandstone and siltstone 16 Mudstone with anhydrite nodules
5 Anhydrite and shale 11 Hard halite cemented siltstone 17 Dolomite
6 Very fine sandstone with shale and 12 Anhydrite and dolomite
anhydrite nodules
NOTE Taken from reference [14].
Figure 2 — An example of a composite suite of geophysical logs
4.2.3 Lithological correlation
Correlation is a particularly important use of geophysical logs. Individual sections of geophysical logs may have
distinct shapes or characteristic signatures that can be manually matched with the same features on logs from
adjacent boreholes, thus signifying that the lithological units extend from borehole to borehole.
8 © ISO 2001 – All rights reserved

Such identifications reveal the geometry of the units from which the continuity and boundaries of aquifers can be
established.
Correlation of logs is carried out by curve matching logs of similar types using the same depth scale (Figure 3).
With a number of recent techniques, which include the computer digitization of logs and the direct recording of logs
in the field for replay on different scales in the office, it is possible to correlate or display the logs from a wide range
of sites in a uniform manner for ease of correlation. In particular the logging of disused boreholes in an area of
investigation can also prove productive.
Correlation may also be accomplished using computers. This is particularly useful where the log responses are less
clearly defined and more than two logs per borehole are being assimilated simultaneously.
4.2.4 Evaluation of physical properties
The third purpose of formation logging is for physical property measurements and this permits quantitative
interpretation of geophysical logs.
In certain cases other parameters such as permeability can be estimated where they can be related to, for
example, porosity or clay content by an independent means.
Geophysical logs can be interpreted to determine the following properties: formation resistivity; formation fluid
resistivity (often measured as fluid electrical conductivity); formation resistivity factor; clay content; bulk density;
primary porosity; secondary or fissure porosity; zones of water movement; zones of contamination; aquifer
boundaries; borehole geometry; casing position and type; casing condition, bonding and borehole condition.
4.3 Fluid logging
4.3.1 General
The most important geophysical logs run, for investigating the borehole fluid column, are borehole flowmeter logs
(both mechanical and thermal), fluid conductivity logs and fluid temperature logs. Fluid logs are run for three main
reasons:
a) to determine flow in the borehole;
b) to identify regional groundwater movement;
c) to assess groundwater quality.
4.3.2 Flow in the borehole
The existence of an open borehole may connect zones of differing in situ hydraulic head and water quality.
Recognizing and understanding the effects of natural flow mixing by use of fluid logs is often important to the
general hydrogeological interpretation of the site. During the drilling and subsequently with time, flow mixing will
occur within the water column (see Figure 4).
When pumping or artesian movement induces flow conditions, fluid logging can accurately determine the depths
from which the yield of the borehole is being derived. In fissured aquifers, fluid logs will indicate those fissures that
are contributing yield. Accuracy will increase if supported by temperature logs.
Where a borehole penetrates more than one aquifer the contribution from each can be identified. Using flowmeters,
quantitative measurements of the flow being derived form each zone or horizon of interest are often carried out.
In appropriate situations, fluid logs can be taken in recharge boreholes or through a packer assembly to identify
active fissures, flow rate and direction, and water quality changes with time. This requires careful consideration of
borehole access arrangements.
Evidence of cascading and seepage can be obtained from closed-circuit television (CCTV) logs.
Key
1 Natural gamma-ray log, radiation, in counts per second increase to the right 4 Local well number
2 Well casing 5 Bedding units
3 Well screen interval
NOTE Taken from reference [16].
Figure 3 — Correlation between boreholes using natural gamma-ray logs
10 © ISO 2001 – All rights reserved

4.3.3 Identifying regional groundwater movement
This type of logging involves repeating logs over a period of time in a network of boreholes to monitor a particular
parameter that is indicative of lateral groundwater movement. An example would be a borehole near a river. The
logging of fluid temperature and fluid conductivity profiles in a series of observation boreholes between the
abstraction borehole and the river, may indicate a tongue of river water being drawn towards the pumped borehole.
These techniques have a particular application to the monitoring of landfill sites, where the movement of fluid
leachate from a site can in some cases be traced using logs run in sampling boreholes drilled around the landfill
area. Determining the direction and extent of leachate flow is a major use of fluid logging and is usually combined
with a chemical sampling program and electrical logging.

Key
1 Ground level 4 Borehole
2 Undisturbed formation porewater profile 5 Fissure flow
3 Fluid log resulting from flow mixing
Figure 4 — Example of the effect of flow mixing in a borehole
4.3.4 Groundwater quality
Fluid conductivity measurements in the borehole give a first indication of the chemical quality of groundwater
present. The conductivity of the water in the borehole may not necessarily be the same as in the formation
alongside; particularly where there are several producing horizons or aquifers present having different hydraulic
heads. Different fluids controlled by the natural hydraulic gradient may invade some horizons. Careful interpretation
of the fluid logging data therefore needs to be made.
Fluid conductivity logging is usually performed under different hydraulic conditions usually without pumping and
during pumping. Overlay plotting of the curves is used to identify locations where log changes, and hence water
movement, takes place.
Inflows of different fluid conductivity, fresher, or more saline waters (often also of different temperature) can then be
easily identified.
Water quality monitoring instruments which simultaneously measure a range of parameters including fluid
conductivity, fluid temperature, dissolved oxygen, pH, redox potential and ion selective possibilities are increasingly
used downhole. They are generally, though not exclusively, run on independent equipment and may make
measurements in depth-profiling or data-logging mode. Currently, equipment typically allows a submergence of
150 m to 200 m, though specialist equipment is available for use at greater depths.
4.4 Construction logging
The purpose of this type of logging is to investigate the condition and construction of a borehole, its casing and any
equipment installed in it. The most commonly used logging method is the three arm borehole calliper. The resulting
log will indicate location of any sidewall features such as collapses, caving, obstructions, washouts and formation
features such as fissures. In the cased section differentiation between plain and slotted screen is commonly
possible and in some cases, casing joints and casing damage can be detected.
Another use of calliper logging is borehole volumetric calculation. Some logging systems carry out this computation
in real time and display the data during logging, but generally, where the calliper log is digitally stored, volumetric
calculations are carried out by software on the replayed data.
Two other logging sondes can be used to examine the borehole casing. One is the casing collar locator that is an
electromagnetic device that detects the joints between casing lengths. The other is the cement bond log that uses
an ultrasonic signal to determine the bonding between cement grout and the casing.
Where water clarity is good, borehole television logging using both axial and radial viewing attachments provides a
very detailed visual log of all the features detectable on a calliper log, in addition to the ability to inspect borehole
equipment such as pumps, transducers, and pipework and detect vertical and oblique fractures not detected by a
calliper log.
4.5 Selection of logs
The nature of the investigation will dictate the geophysical logs required, i.e. whether it is formation evaluation,
determination of the fluid characteristics and flow regime or a check on the borehole construction. The aim of the
logging should be clearly defined and the limitations imposed by borehole construction should be considered so
that the correct suite of logs is selected.
Selection of logs will be constrained by the borehole diameters presence and type of casing and borehole fluid, as
well as the physical limitations of the particular geophysical method. The time available for logging may be
restricted, therefore consideration has to be given to logging speeds and availability of sonde log combinations.
Table 2 summarizes the applications and limitations of geophysical logs and may be used as a guide to their
selection.
It is also necessary to consider the sequence of logging. For example, temperature fluid conductivity and chemical
logs may be carried out during or immediately after drilling. Fluid and formation logging can be used to evaluate the
lithology and groundwater chemistry so that the final depth of the borehole may be determined or a decision made
for optimum location of casing or borehole screen.
12 © ISO 2001 – All rights reserved

5 Planning
5.1 General considerations
Under field conditions, especially where remote or rugged terrain and harsh weather conditions may influence
efficiency and data quality, there is much to be gained from careful and realistic planning. General planning as far
as possible in terms of the provision of equipment and operational procedures will assist in providing better overall
reliability, a consistent approach by different operators and improvements in safety. This should underlie the
detailed preparations required for any specific logging exercise. Planning in a general sense should include
consideration of the following:
a) durability, effectiveness and accuracy of equipment under worst anticipated conditions of vibration, dust,
humidity and weather;
b) reliability of power supplies;
c) layout of equipment and ease of access to instruments for operation and maintenance;
d) versatility of supporting equipment such as cable booms, tripods and pulley arrangements;
e) suitability of vehicles including capacity and manoeuvrability;
f) operator comfort including adequate temperature control, light and seating;
g) routine logging and calibration procedures, pre-log check lists, predetermined conventions for setting up logs,
etc.;
h) safety aspects including internal and external electrical connections and earthing, cable and winch safety,
avoidance of awkward angles, steps and heavy lifting, fire extinguishers and safety kits (including a gas
monitor) and the number of persons on site;
i) the need for fishing tools to recover lost sondes;
j) liability for loss of equipment down the borehole;
k) establishment of a written safety code.

Typical logging
speeds (m/min)
Sidewalled
Free
Centralized
Quality reduces
with increasing
borehole diameter
Open hole
Lined (plastics)
Lined (steel)
Water filled
Mud filled
Air filled
Fissures
Diameter
Caving behind
lining
Collapses
Cement location
Cement bonding
Casing location
Casing features
Water level
Formation fluid
quality
Fluid movement
Borehole fluid
quality
Density
Porosity
Permeable zones
Correlation
Bed boundaries
Bed thickness
Lithology
14 © ISO 2001 – All rights reserved
Table 2 — Application and limitation of geophysical logs
Formation evaluation Fluid properties Construction features Borehole limitations Sonde features
Logging method
Resistivity
(normal, lateral, ■ ■ ■ ■ ■  ■ ■ ■   ■ ■ ■  ■ ■ ■ 5 to 15
focused)
Single point
■ ■ ■ ■    ■ ■   ■ ■ ■  ■ ■ ■ 5 to 15
resistance
Self potential ■ ■ ■ ■ ■   ■ ■     ■ ■  ■ ■ ■ 5 to 15
Induction ■ ■ ■ ■ ■  ■ ■ ■   ■ ■ ■ ■ ■ ■ ■ ■ 3 to 10
Natural gamma ■ ■ ■ ■        ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 2 to 5
Neutron-neutron ■ ■ ■ ■ ■   ■    ■ ■ ■ ■ ■ ■  ■ 3 to 6
Gamma-gamma ■ ■ ■ ■ ■ ■  ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■  ■ 1 to 5
Sonic ■ ■ ■ ■ ■   ■    ■ ■ ■  ■ ■ ■  5 to 10
Temperature    ■ ■ ■  ■   ■  ■ ■ ■ ■  ■ 3 to 10
Fluid conductivity    ■ ■ ■    ■  ■ ■ ■ ■  ■ 3 to 10
Flowmeter     ■ ■    ■  ■ ■ ■ ■ ■ ■  0 to 10
Casing collar
■    ■ ■ ■ ■  ■ ■ 3 to 10
locator
Calliper      ■ ■  ■ ■ ■ ■ ■ ■ ■  ■  ■ 5 to 10
Cement bond       ■ ■  ■ ■ ■ ■ ■  ■ ■  5 to 10
Closed circuit TV ■    ■ ■ ■ ■  ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 1 to 3
NOTE The log response significantly reduces with increasing borehole diameter. The reduction will be greater in cases of resistivity, single-point resistance, induction, spontaneous
potential, temperature, fluid conductivity, flowmeter, casing-collar locator and closed-circuit television logs.

5.2 Safety around wells, boreholes and shafts
Over and above potential hazards arising from the use of the logging system itself, it is important to be prepared in
advance for hazards that might be encountered on reaching the site. Common potential hazards include the
following:
a) drilling site problems related to circulation mud pits, compressed air, slippery conditions or equipment, and
work under drilling masts;
...