Disclosure to Promote the Right To Information
Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public.
इंटरनेट मानक
“!ान $ एक न' भारत का +नम-ण”Satyanarayan Gangaram Pitroda
“Invent a New India Using Knowledge”
“प0रा1 को छोड न' 5 तरफ”Jawaharlal Nehru
“Step Out From the Old to the New”
“जान1 का अ+धकार, जी1 का अ+धकार”Mazdoor Kisan Shakti Sangathan
“The Right to Information, The Right to Live”
“!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता है”Bhartṛhari—Nītiśatakam
“Knowledge is such a treasure which cannot be stolen”
“Invent a New India Using Knowledge”
है”ह”ह
IS 15755 (2007): Hydrometry - Geophysical logging ofboreholes for hydrogeological purposes - considerations andguidelines for making measurements [WRD 3: Ground Water andRelated Investigations]
IS 15755:2007
mimi’i * ray
+EP--r* pim+h *–~a5m3)?wi< ~fiR-G--R
Indian Standard
HYDROMETRY — GEOPHYSICAL LOGGING OFBOREHOLES FOR HYDROGEOLOGICAL PURPOSES —
CONSIDERATIONS AND GUIDELINES FORMAKING MEASUREMENTS
ICS 93.020
@ BIS 2007
BUREAU OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI 110002
June 2007 Price Group 9
Ground Water and Related Investigations Sectional Committee, WRD 03
FOREWORD
This Indian Standard was adopted by the Bureau of lndian Standards, after the draft finalized by the GroundWater and Related Investigations Sectional Committee had been approved by th+ Water Resources Division
Council.
This standard deals with geophysical logging of boreholes, wells and/or shafts (hereafter rei+wed to as boreholes)for hydrogeologic purposes, it provides a measurement of various physical and chemical properties of formationspenetrated 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 geophysicallog.
In the formulation of this standard considerable assistance has been derived from ISO/TR 14685:2001‘Hydrometry determination — Geophysical logging of boreholes for hydrogeological purpose — Considerations
and guidelines for making measurements’.
In reporting the results of a test or analysis made in accordance with this standard, if the final value, observed or
calculated, expressing the result of a test or analysis shall be rounded off in accordance with IS 2: 1960 ‘Rules forrounding off numerical values (revised)’.
It has been assumed in the formulation of this standard that the execution of its provisions is entrusted to
appropriately qualified and experienced people, for whose guidance it has been prepared.
IS 15755:2007
Indian Standard
HYDROMETRY — GEOPHYSICAL LOGGING OFBOREHOLES FOR HYDROGEOLOGICAL PURPOSES —
CONSIDERATIONS AND GUIDELINES FORMAKING MEASIJREMENTS
1 SCOPE
1.1 This standard is a summary of best practice for thoseinvolved in geophysical borehole logging forhydrogeological purposes. It describes the factors thatneed to be considered and the measurements that arerequired to be made when logging boreholes. There
can, however, be no definite standard logging procedurebecause of great diversity of objectives, groundwaterconditions and available technology. Geophysicallogging of boreholes is an evolving science, continuallyadopting new and different techniques. Everyapplication poses a range of problems and is likely torequire a particular set of logs to gain maximuminformation. This standard therefore providesinformation on field practice with the objective of howvariations in measured parameters maybe usefid to takeaccount of particular local conditions. It deals with theusual types of logging carried out for delineation ofaquifer boundaries; mapping aquifer geometry;
assessing the chemical quality and quantity ofgroundwater; water-supply purposes; landfillinvestigations and contamination studies; boreholeconstruction and conditions; and subsurface lithologicalinformation. A basic geophysical logging system isshown in Fig. 1.
1.2 Applications not specifically considered in thisstandard include mineral and hydrocarbon evaluationand geotechnical and structural engineeringinvestigations. However, this standard may be a source
of general information for any borehole geophysicallogging effort.
NOTE— Interpretationof the data collectedduring loggingisreferredto in this standardonlyin a generalway.Forfulldetailsof the analysisand interpretationofgeephysical logs,referenceshouldbe made to specializedtexts.
2 REFERENCE
The standard listed below contains provisions, whichthrough reference in this text, constitutes provisions ofthis standard. At the time of publication, the editionindicated was valid. All standards are subject torevision and parties to agreements based on this
standard is encouraged to investigate the possibility of
applying the most recent edition of the standardindicated below:
IS No. l’ttle
4410 Glossary of terms relating to river(Parts 1 to 20) valley projects
3 TERMINOLOGY
For the purpose of the standard the following definitionsand the definitions given is IS 4410 (Parts 1 to 20)shall apply.
3.1 Air Lifting — Method of producing a dischargeof water from a borehole by the injection of compressedair.
3.2 Argillaceous — Containing clay minerals.
3.3 Bed Resolution — Minimum bed thickness thatcan be resolved.
3.4 Bonding — Seal between a borehole lining andthe geological formation.
3.5 Cable Boom — Rigid support from which thegeophysical sonde and cable are suspended.
3.6 Calibration Tail — Section of field log carryinginformation on sonde calibration.
3.7 Casing String — Set of lengths of casingassembled for lowering into a borehole.
3.8 Composite Log — Several well logs of the sameor similar types suitable for correlation, spliced togetherto forma single continuous record.
3.9 Core — Section of geological formation obtainedfrom a borehole by drilling.
3.10 Curve Matching — Comparison of individualborehole data in graphical form with standard or control
data.
3.11 Drilling Circulation — Movement of drillingfluid (air foam or liquid) used to clear the boreholeduring drilling.
3.12 Fishing Tool — Grappling equipment used tolocate and recover items from within a borehole.
1
1—133 Bls/ND/07
IS 15755:2007
9—
L!16
87
J
I
Q-17
{r!zq18—
7
1
II
f%! ;-L I. 2, 1
I.
I● 21 22 23. I
4A
f
L——L--——J— —J24
Key
1
23456789
10
11
12
13
14
15
16
17
18
13
20
21
22
23
24
Sensor
Electronic section
Cable head
Sonde
Power (down)
Signal (up)
Logging cable
Cable-measuring sheave
Recorder drive
Winch
Slip ring
Ground (electric logging)
Motor
Signal
Power
Vertical scale control
a.c. power source (regulated)
Recorder
Depth indicator
Varying d.c. voltage (mV) for drivingrecorder pens
Logging speed and direction
Downhole power (not universal)
Signal conditioning; zero positioning;sensitivity; time constant etc
Logging controls
FIG. 1 SCHEMATICOFA BASIC GEOPHYSICALLOGGINGSYSTEM
2
3.13 Flushed Zone — Zone at a relatively shol t radialdistance fmm the boreholc immediate y behind trlern~dcake where all of Ibe per? spaces are filled withboreliole fluid.
3.14 Fluid Column — That part of a borehole filledwi.h fluid.
3.15 Geophysical Log — Conkuous record cf a
physical or chemical prope~ty plotted against depth ortime.
3.16 Grain Size — Principal dimension of the basicparticle making up rm aquifer or lithclogical unit.
3.17 Header Information -— Description of ty~)e of
data required for inclttsicm in a table or as input to acomputer programme.
3.18 l~vaded Zone — Portion of formationstxrounding a borehole into which driiling fluid haspartiaily penetrated.
3.19 Jig -– Calibrating device for logging sorrdes.
3.20 Leachate — Liquid that has percvlatcd thrrmgh
solid wastes.
3.21 Loggin~ — Recording of data.
3.22 Mudcake — Residue deposited on the bo;eholewall during drilling.
3.23 Packer — Device placed in a borehole to seal orplug it at a specific ~oint.
IS 15755:2007
3,24 Photomultiplier — Electronic device foramplifying and converting light pulses into measurableelectrical sign ah.
3.25 Plummet –-Plumb bob used for determining theapparent depth of a borelwle.
3.26 Rising Main — Fpe carving water from withina well to a point of dischal ge
3.27 Saline Interface — Boundary between watersOf differing salt content.
3.28 Sidewalling - Rtmrting a i~g up or down aborehole with the sonde in contact with the boreholewall .
3.29 Sonde –- Cabie- surpended probe or toolcomaining a sensor.
3.30 Washout — Cavity f~rmeci by the action ofdr+llitig.
4 UNITS (IF MEASUREMENT
Table 1 gives a list of parameters and tmits ofmeasiirement intended fcr use in this standard.
5 PURPOSE OF GEOPHYSICAL LOGGING
5.1. General
Ideal!y, every borehole drilled for hydrogeologicalpurposes should be geophysically logged. For a smallpercentage (typically 2 perceat to 10 percent) of the
Tabie 1 Parameters and Units of Measurement
(Clause 4)
::’i:BZ:c’T’=~<lR
%“f::i;.:::>p=Spontaneouspotential(SP)
Percent“matrix”porositywherematrixhas Neutron;gamma-gamma;sonicto be stated as sandstcne, hmestone 01
p9%R!&=-- zT’–=-
Gamma-gamma(Ccmptoneffect) —
: :Z*A==== ~E2?Ern’ure
, viii)%i~t-mpcrature
—— .——xi) Coirducti</i~ygiadiect S/mz
T
Differentialconcirrccitity.——xii) Fluidvelocity mmls FtowmeteC heat pulse flowmeten packer-
flowmeter(?FM); repeatedfluid conductivity/temperaturelogging—._ —— —
yjii) Borenolediameter-
mm Calliper——XIV) I Gmrentbonding
-f a
——percent
I ~v) ~caGG==---—
Sonicbond—.———— —mV CasingcollarIocat(on(CCL)
——— .— ———
3
IS 15755:2007
cost of drilling a borehole, the return of informationderived from geophysical logs can far exceed thatderived from drilling samples. Logging costs are aneven smaller percentage of total costs for developing agroundwater source or remediation of contamination.
Many geophysical logs can continuously sample manytimes (10 or more) the volume of the cores even incases where borehole is totally cored and 100 percentrecovery is achieved.
Not only are coring and subsequent laboratory analysisvery expensive, they are also time-consuming. Long-term storage of cores presents problems but digital data
of geophysical logs can be stored and retrieved easily,While there can be no substitute for high qualitylithological samples for determining strata
classification, Iithology, mineral content and grain size,the geophysical log provides in-situ data on thehydrogeological regime around the borehole. It alsoprovides correction for the depth uncertainty of logs
during sample collection.
Boreholes drilled for hydrogeological investigation arenot often cored and good sample collection techniquesare often difficult to achieve. Sample quality isunpredictable in these circumstances and sampling willnot be possible where drilling circulation is lost. It isin such situations that geophysical logging provides acontinuous quantitative set of data when compared withthe drilling samples, which are always subjective.Furthermore geophysical logging can be used in old
boreholes where geological records are undocumented.
In addition to Iithological interpretation, a number ofphysical and chemical properties of the surrounding
rock and fluids contained therein can be investigated.
Geophysical logs can be run in all boreholes includingthose cased with metal or plastic casing and filled withwater, 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 geologicalformation is limited to the nuclear logs and, with plasticscasing, induction logs may also be used. Conventionalresistivity logs (especially focused ones) are possibleto use in plastic screens.
The wealth of information from geophysical logs meansthat they can be used in many spheres ofhydrogeological investigation; for example, in waterresources projects to investigate aquifer hydraulics and
distribution of yield within an aquifer or group ofaquifers. In the rapidly expanding field of groundwaterquality control, geophysical logging is now extensively
used to monitor groundwater pollution, to trace leachatemovement and to monitor the boundaries betweensaline interfaces.
Borehole logging is also important in investigating thedeep hydraulic and hydrogeological properties of rocksin geothermal “and radioactive waste disposal projects.There are a number of engineering applications ofgeophysical logging for investigating boreholeconditions 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 fromminutes to years, adding a new dimension to the
information obtainable. This is particularly applicaMe
to aquifer hydraulics and recharge and pollution studies.
Geophysical logs also provide information that can bedirectly used in surface geophysical studies forstandardization and calibration of parameters. For
example, sonic logs can be calibrated with seismicsections and resistivity logs can be compared withsurface electrical resistivity surveys for resistivity
standardization.
5.2 Formation Logging
5.2.1 General
No geophysical log has a unique response to a particularrock type or-named stratigraphic unit and at somepointin any hydrogeological investigation the formation logs
have to be referred to a borehole with a well-describedset 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, particularlythose which have been cored, The three main purposes
of formation logging are described in 5.2.2 to 5.2.4.
5.2.2 Identification of Lithology
Geophysical logging can provide a very detaileddescription of subsurface formation lithologies. Somelogs such as the natural gamma log commonly provide
an unambiguous delineation of shale and shale-freezones, with the SP and electrical resistivity logs
supplying supporting evidence. Other logs are generallynot diagnostic on their own but in combination canprovide accurate information. The combination ofcalibrated neutron porosity and density logs, forexample, will differentiate sandstone, limestone and
dolomite of different porosities. The additionalinformation provided by the sonic log enables the
identification of halite, gypsum and other minerals,
Where calibrated logs are unavailable, differentiationof lithology will require some geological knowledge,this often being obtained from examination of core
4 ...
b=1 2
3 2
4
f=
5_
50 6
7
7 —,
9
F10
100+ 13 .
E==L
14 2
14
15 /2 —
L==16
.7
IS 15755: 20f37
LITHOLOGY CALLIPER GAMMA-GAMMA GAMMA SP RESISTANCE NEUTRON-NEUTRON
Kev
1
2
3
4
5
6
7
8
Poorly cemented very fine sandstone and 9
siltstone
Anhydrite10. .
Very fine sandstoneII
Very fine sandstone and siltstone with ‘2anhydrite 13
Anhydrite and shale
Very fine sandstone with shale and anhydrite ‘ 4nodules 15
Halite veins and nodules in very fine sandstoneand siltstone
Halite cemented very fine sandstone and siltstone
Hard halite cemented siltstone
Anhydrite and dolomite
Siltstone grading down into mudstone withanhydrite and halite veins and nodules
Mudstone
Mudstone with halite veins
Very fine sandstone and siltstone 16 Mudstone with anhydrite nodules
Halite veins in siltstone 17 Dolomite
FIG. 2 AN EXAMPLE OF A COMPOSITESUITEOFGEOPHYSICALLOGS
.geophysical log; will normally provide a completelithological desc~ption together with accurate depths
to lithological boundaries.
The use of geophysical log interpretation is a majorfactor in the design of casing strings particularly in largethicknesses of variable unconsolidated alluvialsediments. The positioning of plain and screen casing
ides or cuttings. Where core recovery is incomplete, is commonly based entirely on a natural gamma logrun in a temporarily cased borehole.
5.2.3 Lithological Correlation
An important use of geophysical logs is correlation.Individual sections of geophysical logs may havedistinct shapes or characteristic signatures that can bemanually matched with the same features on logs from
5
2—133 BISINDI07
1S 15755:2007
adj scent boreholes, thus signifjfing that the Iithologicalunits extend from borehole to borehole.
Such identifications reveal the geometry of the unitsfrom which the continuity and boundaries of aquiferscan be established.
Correlation of logs is carried out by curve matchinglogs of similar types using the same depth scale (seeFig. 3). With a number of recent techniques, which
(0UJo!1-I.M2
ol–
include the computer digitization of logs and the directrecording of logs in the field for replay on differentscales in the office, it is possible to correlate or displaythe logs from a wide range of sites in a uniform mannerfor ease of correlation. In particular the logging ofdisused boreh?les in an area of investigation can alsoprove productive.
Correlation may also be accomplished using computers.This is particularly usefil where the log responses are
\
‘N ! ! L-23
L-22
L-21 “>\ i ‘y” 1 1 “=
u\-——-rL--r----tL
L!’.
L-20 ‘\. ‘,1
h——— +-L bw
51 BR
L-19 b~ti
Hlu{llL-2’
---ttfY-----
L-17
,//4L-16
.//
L<l 5 >
L-14
w
30 BR—- 4
~.lb — 5
Key
1 Natural gamma-ray log, radiation, in 3 Well screen interval
counts per second increase to the right 4 Local well number
2 Well casing 5 Bedding units
FIG. 3 CORRELATIONBETWEENBOREHOLESUSING NATURAL GAMMA-RAY LOGS
6
43 B’
less clearly detined and more than two logs per boreholeare being assiml Iated simultaneously.
5.2.4 devaluation of Physical Properties
The third purpose of formation logging is for physicalproperty measurements and this permits qumtitati%-einterpretation of geophysical logs.
In certain cases other parameters such as permeabilitycan be estimated where they can be related to, forexample, porosi~ or clay content by independent means.
Geophysical logs can be interpreted to determine thefollowing properties: formation resistivity; formationfluid resistivity (often measured as fluid electricalconductivity); formation resistivity factor; clay content;bulk density; primary porosity; secondary or fissureporosity; zones of water movement; zones ofcontamination; aquifer boundaries; borehole geometry;casing position and type; casing condition, bonding andborehole condition.
5.3 Fluid Loggiug
5.3.1 General
The most important geophysical logs run, forinvestigating the borehole fluid column, are boreholeflowmeter logs (both mechanical and thermal), tluidconductivity logs and fluid temperature logs. Fluid logs
are run for three main reasons:
a) To determine flow in the borehole;
b) To identi~ regional groundwater movement;and
c) To assess groundwater quality.
5.3.2 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 naturalflow mixing by use of fluid logs is often important to
the general hydrogeological interpretation of the site.During the drilling and subsequently with time, flowmixing will occur within the water column (see Fig. 4).
When pumping or artesian movement induces flow
conditions, fluid logging can accurately determine thedepths from which the yield of the borehole is beingderived. In fissured aquifers, fluid logs will indicatethose fissures that are contributing yield. Accuracy willincrease if supported by temperature logs.
Where a borehole penetrates more than one aquifer thecontribution from each can be identified. Usingflowmeters, quantitative measurements of the flowbeing derived form each zone or horizon of interestare often carried out.
In appropriate situations, fluid logs can be taken in
1?513/33 : Awl
recharge boreholes or through a packer assembly toidenti& active fissures, t-low rate and direction, andwater quality changes with time. This requires carefulconsideration of borehole access arrangements.
Evidence of cascading and seepage can be obtainedfi-om closed-circuit television (CCTV) logs.
5.3.3 Identi~ing Regional Groundwater Movem:nt
This type of logging involves repeating logs over aperiod of time in a network of boreholes to monitor aparticular parameter that is indicative of lateralgroundwater movement. An example would be a
borehole near a river. The logging ot’fluid temperatureand fluid conductivity profiles in a series of observationboreholes between the abstraction borehole and theriver, may indicate a tongue of river water being drawntowards the pumped borehole.These techniques havea particular application to the moni!oriug of landfillsites, where the movement of fluid leachate from a sitecan in some cases be traced using logs run in samplingboreholes drilled around the landfill area. Determiningthe direction and extent of leachate flow is a major useof fluid logging and is usually combined with a chemicalsampling programme and electrical logging.
5.3.4 Groundwater Qacdity
Fluid conductivity measurements in the borehole give
a first indication of the chemical quality ofgroundwaterpresent. The conductivity of the water in the borehole
may not necessarily be the same as in the formationalongside; particularly where there are severalproducing horizons or aquifers present having different
hydraulic heads. Different fluids controlled by thenatural hydraulic gradient may invade some horizons.
Carsfid interpretation of the fluid logging data thereforeneeds to be made.
Fluid conductivity logging is usually performed underdifferent hydraulic conditions usually without pumpingand during pumping. Overlay plotting of the curves isused to identify locations where log changes, and hencewater movement, takes place.
Inflows of different fluid conductivity, fresher, or more
saline waters (often also of different temperature) canthen be easily identified.
Water quality monitoring instruments whichsimultaneously measure a range of parameters includingfluid conductivity, fluid temperature, dissolved oxygen,pH, redox potential and ion selective possibilities areincreasingly used downhole, They are generally, thoughnot exclusively, run on independent equipment and maymake measurements in depth-profiling or data-loggingmode. Currently, equipment typically allows a
submergence of 150 m to 200 m, though specialistequipment is available for use at greater depths.
7
IS 15755:2007
10(
~rkwn
20(
30(
I
IIIIIII\\
\
\
I\
2 \
\
\
\
\\
\\
I500 1000
FLUID CONDUCTIVITY (pS/cm)
Key
1 Ground level
2 Undisturbed formation porewaterprofile
3 Fluid log resulting from flow mixing
4 Borehole
5 Fissure flow
FIG. 4 EXAMPLEOFTHEEFFECTOFFLOWMIXINGIN A BOREHOLE
5.4 Construction Logging
The purpose of this type of logging is to investigatethe condition and construction of a borehole, its casing
and any equipment installed in it. The most commonlyused logging method is the three arm borehole caliper.The resulting log will indicate location of any sidewallfeatures such as collapses, caving, obstructions,washouts and formation features such as fissures. In
the cased section differentiation between plain andslotted screen is commonly possible and in somecases, casing joints and casing damage can bedetected.
8
Another use of caliper logging is borehole volumetriccalculation. Some logging systems carry out thiscomputation in real time and display the data duringlogging, but generally, where the calliper log is digitally
stored, volumetric calculations are carried out bysoftware on the replayed data.
Two other logging sondes can be used to examine theborehole casing. One is the casing collar locator that isan electromagnetic device that detects the jointsbetween casing lengths. The other is the cement bondlog that uses an ultrasonic signal to determine the
bonding between cement grout and the casing.
IS 15755:2007
Where water clarity is good, borehole television loggingusing both axial and radial viewing attachmentsprovides a very detailed visual log of all the features
detectable on a caliper log, in addition to the ability toinspect borehole equipment such as pumps, transducers,and pipework and detect vertical and oblique fracturesnot detected by a caliper log.
5.5 Selection of Logs
The nature of the investigation will dictate thegeophysical logs required, that is whether it is formationevaluation, determination of the fluid characteristicsand flow regime or a check on the boreholeconstruction. The aim of the logging should be clearlydefined and the limitations imposed by boreholeconstruction should be considered so that the correctsuite of logs is selected.
Selection of logs will be constrained by the boreholediameters presence and type of casing and boreholefluid, as well as the physical limitations of the particulargeophysical method. The time available for loggingmay be restricted, therefore consideration has to begiven to logging speeds and availability of sonde log
combinations. Table 2 summarizes the applications andlimitations 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 andchemical logs may be carried out during or immediately
after drilling. Fluid and formation logging can be usedto evaluate the lithology and groundwater chemistryso that the final depth of the borehole may bedetermined or a decision made for optimum locationof casing or borehole screen.
6 PLANNING
6.1 General Considerations
Under field conditions, especially where remote orrugged terrain and harsh weather conditions mayinfluence efficiency and data quality, there is much to
be gained from careful and realistic planning. Generalplanning as far as possible in terms of the provision ofequipment and operational procedures will assist inproviding better overall reliability, a consistent
approach by different operators and improvements insafety. This should underlie the detailed preparationsrequired for any specific logging exercise. Planning in
a general sense should include consideration of thefollowing:
a) Durability, effectiveness and accuracy ofequipment under worst anticipated conditionsof vibration, dust, humidity and weather;
b) Reliability of power supplies;
c)
d)
e)
f)
g)
h)
j)k)
Layout of equipment and ease of access toinstruments for operation and maintenance;
Versatility of supporting equipment such as
cable booms, tripods and pulley arrangements;
Suitability of vehicles including capacity andmaneuverability;
Operator comfort including adequatetemperature control, light and seating;
Routine logging and calibration procedures,pre-log checklists, predetermined conventionsfor setting up logs, etc;
Safety aspects including internal and externalelectrical connections and earthing, cable andwinch safety, avoidance of awkward angles,steps and heavy lifting, fire extinguishers andsafety kits (including a gas monitor) and thenumber of persons on site;
Need for fishing tools to recover lost sondes;
Liability for loss of equipment down theborehole; and
m) Establishment of a written safety code.
6.2 Safety Around Wells, Boreholes and Shafts
Over and above potential hazards arising from the useof the logging system itself, it is important to beprepared inadvance for hazards that might beencountered on reaching the site. Common potentialhazards include the following:
a)
b)
c)
d)
e)
f)
g)
Drilling site problems related to circulation
mud pits, compressed air, slippery conditionsor equipment, and work under drilling masts;
Conditions inside old buildings includingunstable roofs or floors, loose junk, gasaccumulation and exhaust build-up;
Work around large diameter wells/shafts andchambers including gas accumulation belowthe surface, unsatisfactory cover plates andrisks of falling into the well;
Conclitions around deep boreholes includinggas generation;
Work at remote sites lacking help or
communication in an emergency;
Problems with overhead cables and currentleakages; and
Presence of gas and leachate at waste disposal
sites.
A safety code should be made available to all personnelto establish safe working practices in the vicinity of wells,boreholes and shafts. Particular regard should be givento the need for the following equipment or precautions:
a) Adequate safety clothing including helmets,
gloves, boots, etc;
9
3—133 Bls/ND/07
Table 2 Application and Limitation of Geophysical Logs
(Clause 5.5)
IS 15755:2007
b)
c)
d)
e)
0
g)
Approved gas monitoring equipment to detectmethane or, if appropriate, other toxicsuffocating or explosive gases;
Safety harnesses;
A minimum of two persons on site unless
under certain defined circumstances;
Designated no smoking areas;
Prearranged radio communications andreporting procedures; and
A first aid kit.
6.3 Site Access
Planning of the logging exercise should have regard tothe following:
a)
b)
c)
d)
e)
f)
g)h)
Legal rights of vehicular or non-vehicularaccess;
Verbal permission from the owner or tenant;
Physical constraints such as soft or firmsurfaces, width of openings and gates,headroom, gradients, etc;
Damage to crops, fields and fences;
Line of sight access from top of borehole cable
boom or tripod;
Availability of power supply;
Need for stock-proof fencing; and
Noise and nuisance.
6.4 Access Within a Borehole
If logging is to be carried out where there is a risk ofentanglement or wrapping of cables, pressure lines,rising mains or pumps, an access tube should beprovided. This should have a smooth internal profileand a minimum internal diameter of 100 mm and shouldextend not less than 2 m below a working pump. Thediameter and length of the sondes to be used may dictatethat larger access tubes are required. In the case of asmall diameter borehole, dummy runs should be madewith a heavy plummet to ensure free access.
Possible hazards to be considered in designing an
access tube include:
a) Debris falling on top of the sonde or floating
slivers of plastic which can cause jamming; and
b) Snagging that may arise where a small diametertube opens downwards into a larger borehole,particularly where verticality is suspect.
A smooth profile to the cable head and provision of afunnel at the base of the access tube will assist in
trouble-free access.
6.5 Equipment
All equipment should be regularly serviced in
accordance with the manufacturer’s recommendations.It is good practice to maintain logging sondes and rocksand the general working environment in a clean, dust-free condition and to carry out routine pre-loggingchecks on each function. Attention should at all timesbe paid to the condition of the equipment as slowdeterioration can often go unnoticed; in particular thesafety of all electrical connections and the correctcondition and operation of the cable head. Appropriatemeasures should be taken to ensure that any equipmentused in a water supply borehole is washed and sterilizedimmediately before use.
6.6 Borehole Details
To prepare equipment adequately, basic details of the
borehole will be required before arriving at the site.Certain systems with data recording facilities may alsorequire the input of header information orsupplementary comment. It is useful in any case to haveas much data on the borehole as possible in order toaid on-site interpretation. A list of relevant data to beconsidered is as follows:
a)
b)
c)
d)
e)
h)
j)k)
m)
n)
P)
q)r)
s)
t)
Location and national grid reference;
National water well number or other identifie~
Total depth of the borehole;
Standing water level and/or pumping waterlevel;
Date of construction;
Drilling fluid, whether water, mud, air orfoam;
Lining or casing details including diameter,depth, plain or slotted, material (plastics, steel,fibreglass, etc), grouting details, constructionof borehole top and datum levels;
Uncased hole diameters and reductions;
Borehole fluid;
Zones of collapse or possible constriction;
Presence of pump (dip tubes, flanged rising
main, electrical cables, etc);
Likelihood of junk in borehoie;
Methane content of water;
Presence of saline interfaces;
Position of underground services or aboveground cables;
Pumping rates and possible influence of
nearby abstraction of recharge boreholes; and
Presence of contamination, whether fromdirect pollution into borehole, surface layers
of oil or diesel, or leachate plumes.
The precise logging sequence depends on local
conditions and requirements. It is, however, advisable ‘to conduct the logging in a pre-planned sequence, to
11
IS 15755:2007
aid in interpretation and to minimize mutual logdisturbance.
6.7 Logging Sequence
In the case of fluid logging, consideration should begiven in advance to the effects of drilling or otherdisturbing mechanisms in the water column such aspumping. Where appropriate, arrangements may berequired for those to cease, ideally at least 24 h priorto !ogging.
Alternatively, the object of logging a borehole mightbe to determine conditions during pumping. Certainformation logs may be required during or immediatelyafter drilling to evaluate lithology or pore water qualityperhaps to assist in deciding the final depth or theoptimum location of casing or borehole screen.
In the case of an open borehole where specialrequirements do not apply, a suggested loggingsequence might be as follows:
a) Determination of total depth and clear accessto borehole (for example, with plummet);
b) Fluid temperature and conductivity logging;
and
c) Flow logging;
d) Caliper log; and
e) Formation logging.
Although it is important to measure fluid temperature
and conductivity profiles in their undisturbed state as adownhole log, this does require a compromise. It wouldbe unwise to place any expensive logging sonde into a
borehole without prior knowledge of the depth to whichthere is unhindered access. The jamming of a sonde,the coiling of lightweight cables or, at the very least,the clogging of conductivity rings by mud in the base
of hole can largely be avoided by a little care. In newlydrilled boreholes in alluvial aquifers it is wise to waitan hour before logging in case the borehole collapses.A hand-wound plummet is an effective means ofdetecting potential problems arising from obstructions,bridging, collapse or situation. However, theintroduction of such a device may affect the delicate
thermal balance of the water column and interpretation
of the fluid logs should take account of this.
Following fluid logging in this sequence, the caliperlog not only provides a useful aid to on-site
interpretation of subsequent fcrmation logs but alsohighlights in d~tail any potential hazards for larger ormore complex &ndes such as sonic sondes or sondes
containing radioactive sources.
6.8 Quality Assurance
Before, during and after logging a number of checksshould be made on the data and sonde as follows:
a) Calibration checks of the sondes:
1) Each log parameter should be calibratedat the recommended interval;
2) Jig checks should be made in the fieldbefore and after logging; and
3) Calibration certificates should be fullycompleted.
b) During the logging operation, a short repeatsection (typically 5 m to 20 m) of the logshould be recorded in addition to the main runin order to provide a check on equipmentstability and repeatability and in the case ofradiometric tools an indication of statisticalvariations.
c) Other checks include:
1)
2)
3)
Making sure that the sonde depth referencereturns to the log datum within acceptablelimits after each logging run and that any
discrepancy be recorded on the field sheet;
Verifying that the caliper log measurement(where run) agrees with the expecteddimensions of well casings; and
Verifying that the water level detected by
appropriate logs agrees with the waterlevel measured by a conventionalindependent method.
d) Data collected by magnetic recordings shouldbe backed up or the tape given a uniqueidentification.
7’ FORMATION LOGGING
7.1 General
Formation logs respond to the physical properties ofthe geological formations around the well and the fluidsthey contain. The formation logs are described in 7.2to 7.6.
7.2 Electric Logs
7.2.1 Resistivity
7.2.1.1 Property measured
The electrical resistivity of the formation around the
borehole is measured.
7.2.1.2 Applications
Applications for measuring the resistivity include:
a) Determination of formation water quality andthe borehole fluid level;
b) Determination of bed thickness and type;
c) Correlations between boreholes;
d) Determination of porosity; and
e) Detection of casing and/or open hole boundary.
12
IS 15755:2007
7.2,1.3 Principles ofmeasui-ement
7.2.1,3.1 Resistance
The simplest electrical measurement is a single pointresistance (SPR) log, the electrical resistance of theground being measured between one surface electrodeand one downhole electrode. The measurements cannotbe calibrated as resistivity and for this reason the log issuitable for qualitative interpretations only. It is verymuch affected by hole size and fluid conductivity.However, it provides considerable detail and is usefulfor correlation.
7.2.1.3.2 Resistivity
The use of multi-electrode sondes enables resistancemeasurements to be made of known or assumedvolumes of earth and hence the measurements arecalibrated in terms of resistivity. Common electrodearrangements are the 0.4 m (16 in) (short) and 1.6 m(64 in) (long) normal and the 7.5 m (224 in) lateralarrays. The short normal array is designed to measurethe resistivity of the invaded zone of the formation close
to the borehole wall. The long normal and lateral arraysare used to obtain the resistivity of the undisturbedformation beyond the invaded zone. The radius ofinvestigation of normal (potential) electrical sondes isapproximately equal to twice the electrode spacing,while the radius of investigation of the lateral sonde is
about equal to the electrode spacing.
7.2.1.3.3 Other resistivity logs
&l@herresistivity logs have been devised to investigatedeeper into the formation to obtain a more accuratevalue of the formation resistivity. These are thefocused current tools such as the guard and laterolog,which are specifically designed to measure true
readings and relatively high formation resistivities
through conductive borehole fluids. With focusedsondes, a much better vertical resolution (that is, bedthickness evaluation) is achieved than with the short
normal array.
7.2.1.4 Calibration
This is achieved by connection of resistances of
accurately known values to the sonde, prior to logging.
7.2.1.5 Interpretation
Resistivity logs along with porosity information may
be used to determine porewater quality using empiricalrelationships. Resistivity logs are quite useful in
deciphering water-bearing zones and in determiningporosity based on Archie’s empirical relationship asfollows:
F= R,IRW = ll~m
13
where
F = formation factor;
R, = formation resistivity;
RW= formation fluid resistivity;
~ = porosity; and
m = cementation factor.
7.2.2 Spontaneous Potential (SP)
7.2.2.1 Property measured
Electrical potentials caused by electrochemical and
oxidation-reduction differences occur at the contact ofthe geological strata with borehole fluid and at thecontact between the geological strata. A singleelectrode, usually made of lead, is run down theborehole and the potential difference is measuredbetween this electrode and one placed at the surface.
7.2.2.2 Applications
Applications for determining the spontaneous potentialinclude:
a) Lithological identification; and
b) Determination of formation water resistivity.
7.2.2.3 Principles of measurement
The SP is a function of the chemical activities of fluids
in the borehole and adjacent formation. It is thecombination of membrane, liquid junction andstreaming potentials. The SP is measured in millivolts.
7.2.2.4 Calibration
The system is calibrated using known potentials overthe range of the instrumentation.
7.2.2.5 Interpretation
The primary function of this log in groundwaterapplications is as a sand/clay indicator or limestoneindicator. However, porewater conductivity, and hencequality, can be estimated from certain empirical formulaeusing SP logs provided there is sufficient electrochemical
contrast between the fluid in the borehole column andformation porewater fluids. The borehole fluid resistivityis determined through a mud resistivity meter. However,
these conditions are seldom met in fresh water aquifersand errors in these estimates can be large.
7.2.3 Induction
7.2.3.1 Property measured
Electrical conductivity of the formation around theborehole is measured.
7.2.3.2 Application
Applications for determining induction include:
IS 15755:2007
a)
b)
c)
d)
e)
Determination of true formation resistivity;
Measurement of bed thickness and type;
Correlations between boreholes;
Fracture location in low porosity fresh waterformations; and
Usage in open or plastic-cased boreholes, thatare air, water or mud filled.
7.2.3.3 Principles of measurement
The induction sonde comprises between two and six
coaxial coils (focused tools) one of which is thetransmitter and another is the receiver (main coils) coilspaced between 0.7 m and 1 m apart. The remainingcoils (focusing coils) are used to improve vertical andradial resolution of the device.
The transmitter coil is energized by high frequency
alternating current. The resulting magnetic field inducessecondary currents in electrically conductiveformations; these in turn create magnetic fields inducingsignals in the receiver coil.
These signals are proportional to the conductivity(reciprocal of resistivity) of the formation. Any signalsproduced by direct coupling between the transmitterand receiver in the measuring circuits are balanced out.
7.2.3.4 Callbraiiox
A calibration loop is accurately positioned around thetool that induces a signal in the receiver coils that
corresponds to a fixed conductivity value.
7.2.3.5 Interpretation
Provided the formation has not been deeply invaded
by the drilling fluid, then the induction log values areclose to the true formation resistivity. Induction logstnay be run in air-filled and plastic-lined holes (seeTable 2).
7.2.4 Limitations of Electric Logs
Electric logs cannot be run in cased (metal or plastic)
or air-filled boreholes. Induction logs cannot be run in
mc(al-cased holes. Also, active electrolytic corrosion
of the casing may give rise to spurious potentials on
the self-potential log (see Table 2).
7.3 Natural Gamma-Ray Logs
7.3.1 Property Measared
The natural gamma-ray log is a measure of the naturalradiation emittecl as a result of the disintegration of theradioactive elements uranium, thorium and potassium.These are concentrated in minerals such as feldspar,mica, glauconite and clay minerals. Within sedimenta~rocks, the potassium-40 isotope contained in clay
minerals is mainly used in the evaluation of clay (shale)content.
7.3.2 Applications
Applications for natural gamma-ray logs include:
a) Lithological identification,
b) Correlation purposes, and
c) Clay content evaluation.
7.3.3 Principles of Measurement
The sonde normally consists of a scintillation counter,
commonly a sodium iodide crystal and photomultiplierand its associated electronics.
Gamma-ray emission is statistical in nature; theresultant electronic signals are a series of randompulses. The statistical variations can be reduced byaveraging a number of pulses recorded during a giventime or depth interval.
A statistical check can also be carried out by holdingthe sonde stationary in the borehole opposite well-defined strata and recording the log response over agiven period of time.
7.3.4 Interpretation
The log is mainly used for lithological identification to
distinguish clays, shale and marls (high gamma activity)from sandstones and carbonates (low gamma activity).
Correlation of logs from multiple boreholes can be
accomplished using gamma-ray logs as shown in Fig. 3.Normal gamma-ray logs can be run in cased holes.
7.3.5 Calibration
The log may be calibrated by using a small source ofgamma radiation set in a jig that is related to a standardresponse following the instructions provided by themanufacturer.
7.3.6 Limitations
An increase in hole diameter decreases the gamma logresponse. The presence of water, casing and grout also
affect the sensitivity of the log, as do crystal size,logging speed and filter characteristics.
7.4 Neutron-Neutron (Porosity) Logs
7.4.1 Property Measured
The neutron log is a direct measurement of the hydrogen
content of the formation.
7.4,2 Applications
Applications for neutron-neutron (porosity) logsinclude:
a) Delineations of saturated porous formations;
14
IS 15755:2007
b) Determination ofmoisture content (porosity);and
c) Correlation purposes.
7.4.3 Principles of Measurement
The neutron tool contains a source of high-energyneutrons (commonly americium-beryllium) withthermal neutron detectors at fixed distances away fromthe source (that is, 200 mm or 480 mm). The emittedneutrons collide elastically with the atoms in the rock.The neutron mass is essentially the same as that of
hydrogen, hence collisions with hydrogen atoms causethe maximum energy loss. Thus, with hydrogen present,the number of neutrons counted at the detector will beinversely proportional to the number of collisions takingplace and hence the hydrogen content. Since water isthe main source of hydrogen in rocks, the neutron logcan be calibrated to measure the total water content(porosity) of the formation. Similar statistical checksto the natural gamma-ray log are made.
7.4.4 Calibration
Calibrating sleeves related to standard responses areplaced over the sonde following the instructionsprovided by the manufacturer. Alternatively, the logsmay be calibrated against laboratory porositydeterminations on core samples for a given aquifer.
7.4.5 Interpretation
The log is interpreted along with other logs so thatcorrections may be made for the hole diameter and
lithology. When calibrated, porosity values can be readdirectly from the log. As the log measures the totalhydrogen content of the formation, high responses canbe expected for clays (high water content) and coal(high hydrocarbon content).
7.4.6 Limitations
Increases in the borehole diameter give rise to falseporosity values unless corrected. Ideally, neutron logsshould be run in small diameter boreholes (less than300 mm diameter). Casing reduces the log response by
holding the tool away from the formation. The presenceof grout or plastic casing reduces the neutron logresponse due to, respectively, high hydrogen or high
chlorine contents. Mud cake also keeps the tool awayfrom the wall of the borehole by introducing low-density, high-porosity material between the formation
and tool. Neutron logs cannot be used to distinguishbetween bonded water in clays and free water in sands.
7.5 Gamma-Gamma (Density) Logs
7.5.1 Property Measured
Attenuation of back-scattered gamma radiation as a
function of electron density of the rock surroundingthe borehole is measured.
7.5.2 Applications
Applications for gamma-gamma (density) logs include:
a) Measurement of bulk density;
b) Derivation of porosity;
c) Identification of lithology;
d) Location of cavities and cement outside the
borehole lining; and
e) Correlation purposes.
7.5.3 Principles of Measurement
The sonde contains a source of gamma radiation (such
as cobalt-60 or cesium-137) that is placed at a setdistance from the detector. Shielding prevents radiation
from the source directly reaching the detector;
consequently, most of the radiation arriving at the
detector is via the formation. The gamma radiation isscattered by the atoms in the formation such that thenumber of gamma rays arriving at the detector is
inversely related to the density of the rock.
Some sondes use two or more detectors at differentspacing from the source so as to provide eithercorrection for borehole effects, such as mudcake andsmall irregularities in borehole diameter, or a higherbed resolution capability.
All sondes are run down the side of the borehole while
being pressed against the borehole wall by eitherbowsprings or caliper arms.
7.5:4 Calibration
Primary standards are fresh water-filled limestoneblocks of accurately known densities. Secondarystandards are large blocks of magnesium, aluminiumand a tank of water into which the sonde is inserted.
7.5.5 Interpretation
Lithological identification is possible where a sutlicientdensity contrast occurs between formations such as thatbetween a “clean” (clay free) formation and a shaleformation.
7.5.6 Limitations
Variations in borehole size due to fissures and caving
can result in a loss of contact with the borehole wall.The wall rugosity introduces a source of error from thelow-density medium (fluid, mud, mudcake) between
the sonde and formation. Casing or grout decreases thesensitivity of the log due to increased attenuation ofgamma radiation. The method is not suitable for highlyuncompacted formations.
15
IS 15755:2007
7.6 Sonic Logs 7.7 Other Logs
7.6.1 PropertyMeasured
The acoustic (or sonic) log provides a measure of thevelocity and attenuation characteristics of acousticwaves over a given interval of formation adjacent tothe borehole.
7.6.2 Applications
Applications for sonic logs include:
a) Lithological identification,
b) Porosity,
c) Seismic velocities,
d) Mechanical properties, and
e) Fracturing/permeability.
7.6.3 Principles of Measurement
The sonde consists of one or two transmitters, one ormore receivers spaced at fixed distances apart andassociated electronics. The acoustic transmitters arepulsed at regular intervals and either the time for eachpulse to reach each receiver is measured or the fullacoustic wave form arriving at each receiver is
displayed and recorded. Usually interval transit timeof slowness, in microseconds per metre, is recordedinstantaneously. l-his is the reciprocal value of the sonicvelocity of the longitudinal (P) waves.
7.6.4 Calibration
The times measured are related to an accurate electronicclock within the sonde.
7.6,5 Interpretation
Variations in the P wave (compressional) velocity maybe used to determine changes in lithology and deriveporosity of the formations.
Analysis of the full wave recording (dependent upon
sonde type and conditions) may permit identificationof compressional shear and stonely waves from whichelastic moduli (along with density) and fracture
properties of the rock can be determined.
The attenuation and distortion characteristics of thewaveform may also provide information on fracturing
and permeability y characteristics of the rock.
7.6.6 Limitations
The sonde should normally be run in the middle of
boreholes of up to 500 mm in diameter (dependent upontransmitter and/or receiver spacing and sonde diameter)and in unlined fluid-filled sections. In large diameterboreholes, certain sonde designs may be run sidewalled.
7.7.1 General
Other logging methods are in use in the petroleumindustry and have application in hydrogeophysicallogging, but are used only occasionally. They include,for example, dipmeter measurements, electromagneticpropagation measurements, lithodensity logging,spectral gamma-ray measurements and imaging suchas acoustic televiewer and formation micro-scannerlogging.
7.7.2 Dipmeter
The dipmeter tool provides an apparent dip of beds bycomparing detailed micro-resistivity curves fromopposing sides of the borehole. The verticality of theborehole is also usually measured. An azimuthorientation of the measurements is given by amagnetometer or gyrocompass. The dip is computedfrom the offset of resistivity changes recorded bymultiple electrode arms that contact the borehole wall.Early tools recorded three resistivity curves; moderntools record six or eight curves from three or fourindependent arms.
The dipmeter resistivity and orientation data isprocessed to determine the dip and strike of formationsencountered in the borehole. It can be used to locatefwlts, unconformities, fractures and joints. It isincreasingly used for sedimentology studies.
Because the processing is ccmplex, it is one of the moreexpensive tools to run. A borehole diameter of at least150 mm (6 in) is needed for good accuracy,
7.7.3 Spectral Gamma-Ray
Spectral gamma-ray logging is a variation of naturalgamma ray logging in which the individual proportionsof potassium, uranium and thorium which makeup the
total spectrum are determined by measurements inseveral energy windows. The ratio of these elements isused to identify the types of clay mineral present.
The tool is of larger diameter than natural gamma ray
tools because of the need to use a larger volume
detector.
7.’7.4 Lithodensity Log (Photoelectric Absorption)
The lithodensity log is a variation of the formation
density log that, in addition to bulk density, measuresthe photoelectric absorption index of the formation. Thephotoelectric absorption curve is used to identify thelithology more accurately than the density log because
porosity and the pore fluid have less influence on it.Used together with spectral gamma measurements, itcan also identify clay minerals that may be present in
the formation.
16
7.7.5 Acoustic Televiewer or Borehok Televie~,wr
The acoustic televiewer is a sonic logging method that
uses a rotating transducer to provide an image of theacoustic reflectivity of the borehole wall. The image
shows the borehole wall as it would appear if splitvertically and laid flat. The image is orientated using a
magnetometer inside the tool and is useful for
identifying fractures. Vertical fractures appear as
straight lines; inclined fractures as sinusoidal traces.The direction and dip of the fractures and other
structural features (bedding) relative to magnetic northcan be read from the image.
It can be used in boreholes where conventional videoimages are not available due to poor visibility butcannot be used where there is no mud or water requiredfor the sonic coupling (that is, above the water table orin dry holes).
7.7.6 Formation Micro-Scanner
The formation micro-scanner provides an electrical
image of the borehole wall by measuring electricalconductivity from any array of buttons on pads thatcontact the borehole wall. The electrical measurernentsare processed into orientated images of strips of theborehole wall. The images are two-dimensional andhighly resolved and can be used to identify bedding,fractures and sedimentary features. It is an expensive
tool to run and is not normally used in water wells.
8 FLUID LOGGING
8.1 General
These logs record the properties and movement of waterwithin the borehole. The parameters measured aretemperature, electrical conductivity and flow.
8.2 Temperature
8.2.1 Property Measured
Temperature of the borehole fluid surrounding the
sonde is measured.
8.2.2 Applications
Applications for logging the temperature of theborehole fluid include:
a)
b)
c)
d)
Detection of fluid movement within the
borehole;
Identification of zones of in flowloutflow(including casing leaks) within the borehole;
Determination of geothermal gradient; and
Data provided for the correction of other logs
such as fluid conductivity and formationresistivity.
IS 15755:2007
8.2.3 Principles of Measurement
The sonde contains a thermal detector, thermistor orsolid state device and its electronics.
Recording of the absolute fluid temperature is done.Differential temperature is also obtained by measuring
the difference between two depths (typically 0.25 m to2.5 m apart) using two sensors or more commonly bydigital techniques. Differential logs are particularlyuseful as small changes in the temperature gradient aresharply accentuated.
8.2.4 Interpretation
There is a natural geothermal gradient of increasing
temperature with depth. This gradient varies with the
thermal conductivity of the geological formation and
is modified by water flowing in and out of the borehole.
Interpretation of the log can determine the flow patternwithin the borehoie.
8.2.5 Limitations
The log may be run in all sizes of borehole, although invery large diameter wells thermal variations across thewell may affect the results.
The borehole fluid is disturbed during logging.
Consequently, this log should be run first in a downwarddirection (and normally combined with fluidconductivity y).
Drilling, cementing and pumping disturbs the thermal
environment of the borehole fluid and time should beallowed for the borehole fluid to approach equilibriumprior to logging.
8.3 Fluid Conductivity
8.3.1 Property Measured
The electrical conductivity of the borehole fluid is
measured.
8.3.2 Applications
Applications for logging the fluid conductivity include:
a) Determination of borehole fluid quality; and
b) Identification of zones of fluid movement into,out of and within the borehole.
8.3.3 Principles of Measurement
The fluid conductivity sonde usually contains a series
of encased electrodes of inert metal or carbon. Analternating current is passed between one pair ofelectrodes and the resultant voltage across another pairis measured. Conductivity may also be measured by
electromagnetic methods whereby coils are used inplace of electrodes.
17
IS 15755:2007
Differential logs are particularly useful as small changesin conductivity are sharply accentuated.
8.3.4 Calibration
The sonde is placed in fluids of known electricalconductivity and temperature. Corrections are thenmade to a standard temperature (normally 25”C).
8.3.5 Interpretation
The electrical conductivity of water is related to thetotal dissolved solids and is therefore a measure of thequality of the groundwater.
Charts such as those given in Fig. 5 may be used todetermine the electrically equivalent sodium chlorideconcentration. The conductivity log should always becorrected for temperature, as conductivity is a functionof temperature. The shape of the log trace can indicatezones of inflowloutflow.
Specialized techniques of repeated fluid conductivity/temperature logs in connection with pumping test datacan allow for the calculation of the transmissivity ofinflow zones. This technique is particularly suitable for
lower transmissivities (fractured rocks) and has been
applied in many planned repositories for nuclear waste.
8.3.6 Limitations
This log should be run together with the temperaturelog in an undisturbed fluid column. Drilling, cementingand pumping disturbs the column and sufficient timeshould be allowed for this to settle down prior tologging. If the sonde is allowed to stand in mud at thebase of the hole, or mud on a ledge, subsequent readingsmay be erroneous.
8.4 Flow
8.4.1 Property Measured
Fluid velocity in the borehole is measured.
8.4.2 Applications
Applications for logging the flow include:
a) Determination of flow rates and directionwithin the borehole;
b) Identification of permeable zones;
c) Location of casing leaks; and
50 100 200
I I
20000 10000 5000 2000 1000 500 200 100 50
CONDUCTIVIW, I.&cm
FIG. 5 ELECTRICALLYEQUIVALENTCONCENTRATIONSOFA SODIUM CHLORIDESOLUTIONAS A
FUNCTIONOF CONDUCTIVITYOR RESISTIVITYANDTEMPERATURE
18
1S 15755:2007
d) Dr[ermination of \’ertical profile of
permeability or transmissivity (in connectionwith pumping test)
8.4.3 Principles of Measurement
There are several means of measuring vertical flow in
boreholes, dependent on the magnitude of the anticipatedvelocities. The most common is an impeller type thatconsists of a turbine whose revolutions against time arecounted. The mnge of flows measurable by this methodis 30 mmh to 5000 nuds. Velocities lower than 30 rindsmay be detected using an impeller by applying thedifference method, that is running the impeller both upand down the borehole at constant speeds and notingthe differences between the two logs. For high velocities,the impeller may beheld stationary at points of interest.
Low-flow measurements may also be made usingspecialized techniques such as head-pulse, packer-flowmeter, tracer methods or repeated fluid
conductivity and/or temperature logging. Othermethods such as electromagnetic measurement of floware currently being introduced.
8.4.4 Calibration
Flow measuring sondes may be calibrated in specialflow rigs or in the lined sections of a borehole undercontrolled pumping or recharge.
8.4.5 Interpretation
Flow mte can be calculated from a combination of fluidvelocity and calliper logs.
8.4.6 Limitations
Corrections for borehole diameter changes have to bemade. The sonde should, if possible, be centralized in
the borehole. Some flowmeters can only be run in onedirection either up or down the borehole. Otherflowmeters can be used only in clean water conditions
(after flushing or pumping) because of optical detectionsystems.
Figure 6 shows the recommended fluid logging methodfor ranges of discharge and permeability.
9 CONSTRUCTION LOGGING
9.1 General
There are several sondes available to measure the
physical characteristics of the borehole constructionsuch as diameter, depth to casing, location of casing
joints and the integrity of the cement grout.
Additionally, some of the logs in the previous sections
have applications in constructional determinations, suchas the density log for detection of cavities behind thecasing and temperature for grout location.
9.2 Caliper
9.2.1 Property Measured
The sonde measures the diameter cf the borehole.
9.2.2 Applications
Applications for logging the diameter of the boreholeusing a caliper include:
a) Location of casing, type and breaks;
b) Location of diameter changes in the boreholeand packer settings;
c) Location of fractures/fissures and otheropenings;
d) Identification of soft and hard formations;
e) Provision of data for correcting othergeophysical logs; and
f) Calculation of borehole volume.
9.2.3 Principles of Measurement
Calipers are mechanical devices consisting of one tofour spring-loaded arms held against the borehole wall.Any movement of these arms maybe arranged to givea mean diameter or two orthogonal diameters (x-ycaliper). Calipers are often run as part of a combinationsonde and measurements always taken while moving
the sonde up the borehole.
9.2.4 Calibration
Calibration is carried out using jigs or cylinders thatenable an arm to be set at different radii.
9.2.5 Interpretation
The log shows borehole diameter changes, which canbe attributed to drill bit changes, washouts, fissuring,daving and mudcake formation.
9.2.6 Limitations
The presence of rising mains, pumps and otherhardware in the borehole will give erroneous results.
Silts, sands and mud may prevent the caliper arms fromoperating correctly.
9.3 Casing Collar Locator
9.3.1 Property Measured
This log measures the changes in the. magnetic flux dueto the magnetic property of the material present.
9.3.2 Applications
Applications for logging the magnetic, flux using a
casing collar locator include:
a) Location of other magnetic hardware such as
rising mains, pumps and debris; and
19
IS 15755:2007
Key
DISCHARGE(//s)
.-2
10
10”
1
10’
104
—
3
2
1
~.10
10 108 106 104 102 1
Vefy Low Low Medium High
PERMEABILITY
TRANSMISSWIY(m2/s)
1
2
3
Temperature/fluid electrical conductivityheat pulse flowmeter
Packer flowmeter
Flowmeter
FIG.6 RECOMMENDEDFLUTDFLOWLOGGINGMETHODSFORRANGESOFDISCHARGEAND PERMEABILITY
b) Control log for other geophysical logs that areaffected by the presence of casing.
9.3.3 Principles of Measurement
The casing collar locator device consists of a magnet
and coil arrangement. Changes in the magnetic fluxcaused by the variation of casing thickness results in aninduced voltage. The log is run at constant speed and
sharp changes in the record indicate casing collars, etc.
9.3.4 Calibration
Calibration as such is normally not necessary, other thanadjustment of the electronics for the required sensitivity.
9.3.5 Interpretation
The log curve is generally a base line with periodic
20
marks (or pulses) indicating the depths at which thereis a change in the amount of metal present.
9.3.6 Limitations
The position of the sonde in the borehole affects the
magnitude of the signals. For this reason, in largediameter boreholes, the sonde should be run close tothe side. Changes in logging speed give erroneousreadings. The log can be susceptible to electrical noise,
such as that from nearby electrical pumps.
9.4 Cement Bond
9.4.1 Property Measured
The cement bond log is obtained using a sonic sondewhere the amplitude andlor waveform of the received
acoustic signal is measured.
II L —.———— -.
IS 15755:2007
9.4.2 Applications
Applications for logging cement bonds include:
a) Determination of the amount of bondingbetween the steel casing, cement grout andformation, or degree of channeling within thegrout; and
b) Location of the cement seal.
9.4.3 Principles of Measurement
Steel casing suspended freely (unbended) in a fluid-filled borehole transmits elastic energy at a velocity of
5340 mh with little attenuation over the transmitterreceiver spacing. When cement is present and properlybonded around the casing, the elastic energy isdissipated before reaching the receiver. The receivedamplitude is therefore a function of bonding.
9.4.4 Calibration
At a level of 100 percent bonding the signal amplitude
should ideally be zero; this point can be obtainedelectronically. The Opercent bond position of the sondecan be obtained by setting the sonde in freely suspendedlengths of casing.
9.4.5 Interpretations
Variations in the amplitude curve are interpreted in
terms of the casing cement bonding. Corrections haveto be made for casing joints. More commonly, the fullwave form is recorded and displayed in variable density
format which allows easier identification of bondingof the casing.
9.4.6 Limitations
The sonde should normally be run centralized (typicallyin boreholes up to 500 mm diameter, dependent upon
transmitter, receiver spacing and sonde diameter) andin steel-lined fluid-filled sections. In large diameter
boreholes, certain sonde designs maybe run sidewalled.
9.5 Closed Circuit Television Log
9.5.1 Property Measured
Physical features of borehole are measured and recorded.
9.5.2 Applications
This log not only measures the depth of visual features
but also is useful for checking the condition of wellcasing or screen, examining geological features alongthe borehole walls, identifying collapses andobstructions, and for examining installed pipework.
9.5.3 Principles oflleasurement
A video signal from the borehole closed circuittelevision camera is sent to the surface control unit via
21
the logging cable. Many closed circuit televisionsystems are operated with a special cable, especiallyin the case of deep boreholes (more than 300 m). This
surface equipment includes a monitor and videorecorder. Logging and borehole information, including
depth, is also recorded using a television writer.
The camera should be fitted with” lenses and lightsources to facilitate forward views (looking down theborehole) and a rotating side view to examine theborehole well or construction.
Some cameras may have devices that can be fitted torecord directionrd orientation.
9.5.4 Interpretation
The pictures obtained may be difficult to interpretwithout other geophysical logs and require experienceon the part of the operator to make a full anrdysis.
It is possible to evaluate flows witiln the borehole, either
by observing the movement of suspended particles orby attaching lightweight streamers within the field ofview of the camera and noting their movement.
Evidence of cascading and seepage can also be obtainedby this method.
.9.5.5 Limitations
None of the visual information is quantitative. Theclarity of the picture is affected by particulate matterin the borehole fluid which reflects light, causing flaringon the screen. Picture quality is also reduced in largediameter boreholes.
10 LOG PRESENTATION
10.1 General
Geophysical logs are an invaluable record and shouldbe clearly presented for proper interpretation. Logs filedaway with no header information and only crypticannotation can be virtually useless when the details oflogging have been forgotten.
The standards of presentation suggested here are inkeeping with generally accepted practices and with theoutputs from a wide range of instrumentation.
On-site log output is usually from a multi-channel chartrecorder in the form of plotted or printed-paper output.
Digital logging systems often provide the facility toreplay logs off-site, allowing for clean and suitably-
scaled versions to be produced.
Whether conducted for in-house purposes or by a servicecompany, the resulting logs have to be capable ofinterpretation by others.The site and logging information
sheets as shown in Fig. 7 and Fig. 8, provide informationto identify the borehole and have to describe all loggingactivities and details of equipment used.
~. —.—I OGC ‘-_’__’_r--”--- LOG TVpe
—1
yell nmle,’nurnber+
—— .—— ——Location
l-— — riI .——. — .
-Permanent datum I Ekavaticn ‘-r——+=-i–+-
~__i
, 7logs—— —-.
13g mwwured from
____._J:T ‘– - .+yLII- -– —Drilling measured from
Run No. Boret,ole record Casiim record
l++Equipment, logging and recordirig data \
. — ———Log t,pe --i
f-fun W.
}-
‘—-~alibration type—.—. — -—
Tool No. DiamRter Data
}
——Spacing Data
‘‘ - ,%
i——. —. —- ———
Position Data
Source Type Panel tim~ constant—.Strength !Jff set
+=+
—.Wid~- ___ f-og reco?ti.~– ‘-—-— ,
Digital fdta’ Data inteival-t-
Tape/disk reference
I
I ‘_~~—.__ .-——
Logg!?g speedI
L)epths Frc,m
4
‘-L ~=x-
——To
Interval
REMAHKS ———— .—
I 1- ------ “-– ‘——.
%cal scale ~General 11:— lllzzil:
L Log scales— ——— .— .-
-–----4
L- (Attach log top section t ler?)-—. — _——
FI,3.7 EXAMPLEOF ~ITE AND LOGGING INFORMAIX,N SHEETS:HEADER StiCT:ON
—— .———.— — ——I I
}
(M!ach log tail section here)— ——— .—
Log scales II+
t—
I
~;#=~-penera’ 2_——
1: Detail——. —
—.——— ——Location
—.
———‘Well num6er/name
— .- —
4
FIG. 8 EXAMPLE OF SITE AND LOGGINGINFORMATIONSHEETS:TAK SECTION
22
The example header contains all information necessarytoi common water well logs. It is designed to describetill [hc background information relating to the logwithout any other documentation. The datz requestedare self explanatory and can be used for analogue ordigital logging systems. The header allows for severallogging runs to be merged; for example, a resistivitylog Iun in an uacased borehole can be joined to asubsequent iog and the header will provide details ofboth runs so that quantitative evaluation can be madefor the complete borehole section.
The equipment used has to be described, especially
detector spacing and whether the tool is centralized or
sidewalled. Calibration data should be included in the
space provided to enter jig readings or calibrationcoefficients.
The header can describe up to a six-function tool stringthat is sufficient for water well purposes. Full use should
be made of the remarks space to note any other relevantdata such as circulation loss details.
10.2 Track Layout
Standard layouts are either a plain metric scale grid orpreferably the conventional three-track system. The left
track, track 1, is normally used for gamma, caliper andspontaneous potential logs. The right-hand tracks 2 and
3 are used for ether logs. An acceptable variation is touse tracks 2 and 3 for detailed gamma logs.
A variety of track chart paper width is available
depending on the type of logger used. Analog loggersuse 25 cm width paper and digital loggers use 6.4 cm(2.5 in) width paper. Where a large range of log values
is expected in resistivity or conductivity logs, a three-
track version with logarithmic scales on tracks 2 and 3is available providing the hardware output options that
are suitable. T1ack widths divided into 5 or 10 divisions
and depths in metres are now superseding these.
10.3 Log Parameter Scales
Parametei scales may be chosen which suit the rangeof data and the output of the equipment. It is essential
that the scale title should state if processed logs havebeen corrected or compensated. All logs areconventionally displayed from left to right.
IS 15755:2007
10A Depth Scales
The convention for general logging is a depth scale of1 to 200. Borehole sections where more detail isrequired should be logged at 1 to 50. Logs for regionalcorrelation purposes should be run at 1 to 500. Digitalrecording systems allow logs to be replayed at any depth
scale with only one logging run.
The basis for selection of depth scales is:
a) Depth of borehole to be logged;
b) Thickness resolution required; and
c) Ease of correlation and consiskmcy with otherlogs.
10.5 Composite Logs
Digital log recording and appropriate software can beused to provide very useful composite logs where al]logs from one borehole can be output on one sheet.This is an obvious aid to multi-parameter evaluation
and to produce report-ready logging summaries. Depthscales of 1 to 500 provide 100 m of boreholeinformation on a convenient A3 size plot.
10.6 Differential Logs
As well as reading absolute values of p~rameters, suchas temperature and conductivity, measurements maybe obtained of the difference between two sensors ashort distance (0.25 m to 2.5 m) apart. However, with
digital recording now common, it is normal to computethe differential from measurements using a singlesensor.
Differential logs are commonly computed fromtemperature, conductivity and flow logs for thefollowing reasons:
a)
b)
An abrupt change on a temperature,
conductivity or flow log, which represents awater inflow or tiutflow, is converted to a peakon a differential log. This is thought by manyto be more easily interpreted; and
Strong vertical temperature or flow gradients
can mask smaller changes due to inflows andoutflows at fissures. The differential log
effectively measures the gradient and enablesthe use of more sensitive scales.
23
GMGIPN—I 33 BISINDI07—300
l~uwau of Indian Standards
BIS is a statutory institution established under the Bureau of [ndian Standards Act, 1986 to promoteharmonious development of the activities of standardization, marking and quality certification of goods
and attending to connected matters in the country.
Copyright
BIS has the copyright of all its publications. No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS. This does not preclude the free use, in the course ofimplementing the standard; of necessary details, such as symbols and sizes, type or grade designations.Enquiries relating to copyright be addressed to the Director (Publications), BIS.
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments. Standards are also reviewedperiodically; a standard along with amendments is reaffirmed when such review indicates that no changes areneeded; if the review indicates that changes are needed, it is taken up for revision. Users of Indian Standardsshould ascertain that they are in possession of the latest amendments or edition by referring to the latest issue of‘BIS Catalogue’ and ‘Standards: Monthly Additions’.
This Indian Standard has been developed from Doc : No. WRD 03 (366).
Amendments Issued Since Publication
Amend No. Date of Issue Text Affected
BUREAU OF INDIAN STANDARDS
Headquarters :
Manak Bhavan, 9 Bahadur Shah Zafar Marg, New Delhi 110002 Telegrams: JManaksansthaTelephones :23230131,23233375,2323 9402 (Common to all offices)
Regional O&ices : Telephone
Central :
Eastern :
Northern :
Southern :
Western :
Branches :
Manak Bhavan, 9 Bahadur Shah Zafar Marg
{
23237617NEW DELHI 110002 23233841
1/14 C.I.T. Scheme VII M, V. I. P. Road, Kankurgachi
{
23378499,23378561KOLKATA 700054 23378626,23379120
SCO 335-336, Sector 34-A, CHANDIGARH 160022
{
26038432609285
C.I.T. Campus, IV Cross Road, CHENNAI 600113
{
22541216,22541442
22542519,22542315
Manakalaya, E9 MIDC, Marol, Andheri (East)
MUMBAI 400093 {
28329295,2832785828327891,28327892
AHMEDABAD. BAN(3ALORE. BHOPAL. BHUBANESHWAR. COIMBATORE. FARIDABAD.GHAZIABAD. GUWAHATI. HYDERABAD. JAIPUR. KANPUR, LUCKNOW. NAGPUR.PARWANOO. PATNA. PUNE. RAJKOT. THIRUVANANTHAPURAM. VISAKHAPATNAM.
PRINTED BY THE GENERAL MANAGER GOVERNMENT OF INDIA PRESS,NASHIK