IS 15755 (2007): Hydrometry - Geophysical logging of boreholes … · 2018-11-15 · 3.27 Saline Interface — Boundary between waters Ofdiffering salt content. 3.28 Sidewalling -

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“The Right to Information, The Right to Live”

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“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

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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

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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

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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

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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

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20(

30(

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2 \

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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)


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.


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


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.


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.


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.


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


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.


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.


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.


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


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


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.


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


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.


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).


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


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)


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.


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


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.


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.


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


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.


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.


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


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.


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


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.


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

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This Indian Standard has been developed from Doc : No. WRD 03 (366).

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Amend No. Date of Issue Text Affected

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