5a. resistivity logging

7/17/2019 5A. Resistivity Logging

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RESISTIVITY LOGGINGRESISTIVITY LOGGING


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CONTENTSCONTENTS

What is electrical logging?What is electrical logging?

PrinciplePrinciple

Single Point resistance logs(SPR)Single Point resistance logs(SPR)

Conventional Resistivity LogsConventional Resistivity Logs

Response of Potential and gradient Logs over thin and thick conductiveResponse of Potential and gradient Logs over thin and thick conductive

resistance formationsresistance formations Limitations of conventional resistivity toolsLimitations of conventional resistivity tools

ocused resistivity logsocused resistivity logs

!dvantages of focused resistivity tools over conventional resistivity to!dvantages of focused resistivity tools over conventional resistivity too


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CROSS SECTION OF THE BOREHOLCROSS SECTION OF THE BOREHOL


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TOP VIEW OF BOREHOLETOP VIEW OF BOREHOLE


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WHAT IS RESISTIVITY LOGGINGWHAT IS RESISTIVITY LOGGING??

The electrical resistivity of a substance is its ability toThe electrical resistivity of a substance is its ability to

the flow of electrical current through it. its unit is the othe flow of electrical current through it. its unit is the o

is a fundamental inherent property of substance(meis a fundamental inherent property of substance(me

mineral or rock).mineral or rock).

The measurement of formation resistivity is of The measurement of formation resistivity is of importance for the evaluation of hydrocarbon saimportance for the evaluation of hydrocarbon sa

particularly in the virgin, non-invaded portion of the resparticularly in the virgin, non-invaded portion of the res


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HOW ELECTRICAL RESISTIVITY IHOW ELECTRICAL RESISTIVITY IMEASURED?MEASURED?

Playing *ith the num+er of electrodes and the Playing *ith the num+er of electrodes and the

+et*een them one can measure the resistivity ,+et*een them one can measure the resistivity ,

- either at great depth (up to several feet +eyond the +- either at great depth (up to several feet +eyond the +

giving a measurement inside the virgin .one of the giving a measurement inside the virgin .one of the

(called true resistivity/(called true resistivity/ R,)R,) not too much a0ectednot too much a0ected

invasion of mud ltrate/invasion of mud ltrate/

- or close to the +orehole (called 2ushed-.one resistiv- or close to the +orehole (called 2ushed-.one resistiv

*here mud ltrate has largely replaced the original p*here mud ltrate has largely replaced the original po


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HOW ELECTRICAL RESISTIVITY IS USEHOW ELECTRICAL RESISTIVITY IS USE

Com+ination of the resistivity data *ith porCom+ination of the resistivity data *ith por

measurements and formation-*ater resistivmeasurements and formation-*ater resistiv

kno*ledge allo*s the computation of the *kno*ledge allo*s the computation of the *

saturation in +oth shallo* and deep .ones"saturation in +oth shallo* and deep .ones"

Comparison of these t*o saturation values Comparison of these t*o saturation values an idea of the 2uid mo+ility and/ conse4uenan idea of the 2uid mo+ility and/ conse4uen

allo*s the evaluation of the reservoir produallo*s the evaluation of the reservoir produ


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TECHNIQUES USED TO MEASURETECHNIQUES USED TO MEASURERESISTIVITYRESISTIVITY

6here are several techni4ues in use for measurement of the resistivity" !6here are several techni4ues in use for measurement of the resistivity" !

variations of a common +asic system,variations of a common +asic system,

one (or several) emitter (electrode) sends a signal (electrical current) intone (or several) emitter (electrode) sends a signal (electrical current) int

formation"formation"

7ne (or several) receiver (electrode) measures the response of the form7ne (or several) receiver (electrode) measures the response of the form

signal at a certain distance from the emitter"signal at a certain distance from the emitter"

8enerally/ an increase in the distance +et*een emitter and receiver (cal8enerally/ an increase in the distance +et*een emitter and receiver (calspacing) results in an improved depth of investigation (and a reading nespacing) results in an improved depth of investigation (and a reading ne

at the e:pense of vertical resolution"at the e:pense of vertical resolution"

6he depth6he depth ofof investigation is dened as the point at *hich half the signainvestigation is dened as the point at *hich half the signa

from the invaded .one and half from the uninvaded .one (9 ; 5"&)"from the invaded .one and half from the uninvaded .one (9 ; 5"&)"


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FUNCTION OF THE SPACING VALUE OFUNCTION OF THE SPACING VALUE OCAN CONSIDER TWO MAIN CATEGORIECAN CONSIDER TWO MAIN CATEGORIE

TOOLS:TOOLS:

Long-spacing devicesLong-spacing devices oror macro-devices,macro-devices,

Short spacing devicesShort spacing devices oror micro-devicesmicro-devices oror micro tools,micro tools,


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LONG-SPACING DEVICESLONG-SPACING DEVICESORORMACRO-DEMACRO-DE

6hese devices are one medium to deep readin6hese devices are one medium to deep readin

include,include,

- the conventional electrical survey (


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LONG-SPACING DEVICESLONG-SPACING DEVICESORORMACRO-DEMACRO-DECONTDCONTD

They constitute the focused devices as they hThey constitute the focused devices as they ha

guard electrodes which focus the current emittguard electrodes which focus the current emitt

the central electrode. They are less sensitive tthe central electrode. They are less sensitive t

borehole influence. epending on the spacingborehole influence. epending on the spacing

the nature of the focusing, either , maythe nature of the focusing, either , maythe predominant contribution to the measured the predominant contribution to the measured

under average conditions of invasion.under average conditions of invasion.


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SHORT SPACING DEVICESSHORT SPACING DEVICESORORMICRMICRDEVICESDEVICESORORMICRO TOOLSMICRO TOOLS

6hese tools measure shallo* readings"6hese tools measure shallo* readings"

!ll are mounted on pads *hich are applied against the +orehole *!ll are mounted on pads *hich are applied against the +orehole *a

spring" 6hey are designed to read / +y virtue of their short spacspring" 6hey are designed to read / +y virtue of their short spac

their very shallo* depth of investigation"their very shallo* depth of investigation"


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SHORT SPACING DEVICESSHORT SPACING DEVICESORORMICRMICRDEVICESDEVICESORORMICRO TOOLS CONTDMICRO TOOLS CONTD

6here is very little +orehole 2uid e0ect/ +ut the mud cake contri+utes a 6here is very little +orehole 2uid e0ect/ +ut the mud cake contri+utes a

signal" 6he Schlum+erger micro tools include,signal" 6he Schlum+erger micro tools include,

>L - the microlog (micro-normal and micro-inverse)=>L - the microlog (micro-normal and micro-inverse)=

>LL - the microlaterolog (not to +e confused *ith the>LL - the microlaterolog (not to +e confused *ith the

PL - the micropro:imity log=PL - the micropro:imity log=

>SL- the micro spherically focused log=>SL- the micro spherically focused log=

6he vertical denition o+tained *ith these electrode tools is much ner 6he vertical denition o+tained *ith these electrode tools is much ner t

the longer spacings" Like the L is the only non-focused systemthe longer spacings" Like the L is the only non-focused system

group"group"


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WHY COMBINATION OF THESE TOOLWHY COMBINATION OF THESE TOOLIMPORTANT?IMPORTANT?

! com+ination of deep-/ medium- and shallo* reading tools ena+le! com+ination of deep-/ medium- and shallo* reading tools ena+le

evaluateevaluate


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MEASUREMENT OF RESISITIVITYMEASUREMENT OF RESISITIVITY

T!" #$%%"&T 'I %IT"T!" #$%%"&T 'I %IT"

I& I%"#TI+&, & T!"I& I%"#TI+&, & T!"

"/$I0+T"&TI $%*#" '"/$I0+T"&TI $%*#" '

#+"&T%I# 0!"%" #"+"&T%I# 0!"%" #"&

I* T!" 0+T"&TI T IT&I* T!" 0+T"&TI T IT&

II V(R),V(R), T!"& T!" I**"%"&T!"& T!" I**"%"&1"T'""& T'+ "/$I0+T"&T1"T'""& T'+ "/$I0+T"&T

0%T I20%T I2


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THE NORMAL CONFIGURATION. ON THE LEFT: SCHEMATIC VTHE NORMAL CONFIGURATION. ON THE LEFT: SCHEMATIC VTHE NORMAL DEVICE PRINCIPLE. ON THE RIGHT: THE REAL CONFTHE NORMAL DEVICE PRINCIPLE. ON THE RIGHT: THE REAL CONF


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NON-FOCUSED LONG-SPACING TOONON-FOCUSED LONG-SPACING TOO

6his type of tool is no longer in use +ecause of its dra*+acks" @ut/ 6his type of tool is no longer in use +ecause of its dra*+acks" @ut/

important to revie* the +asic measurement principle in order to +eimportant to revie* the +asic measurement principle in order to +e

understand ho* they *orked and the interest of the focused tools"understand ho* they *orked and the interest of the focused tools"


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THE NORMAL DEVICE PRINCIPLETHE NORMAL DEVICE PRINCIPLE

6he measuring electrode > is situated close to the current electrod6he measuring electrode > is situated close to the current electrod

constant currentconstant current II 2o*s from ! to the remote return @" 6he potenti2o*s from ! to the remote return @" 6he potenti

is measured *ith respect to a reference electrode A (at .ero potenis measured *ith respect to a reference electrode A (at .ero poten

means of a voltmeter" !lthough/ theoretically/ A should +e on surfameans of a voltmeter" !lthough/ theoretically/ A should +e on surfa

BinnityB)/ inductive phenomena necessitate placing it do*nhole/ +BinnityB)/ inductive phenomena necessitate placing it do*nhole/ +

distance from > considera+ly greater than is !distance from > considera+ly greater than is !


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THE LATERAL CONFIGURATION. ON THE LEFT: SCHEMATIC VIEWTHE LATERAL CONFIGURATION. ON THE LEFT: SCHEMATIC VIEWLATERAL DEVICE CONFIGURATION. ON THE RIGHT: THE REAL CONFILATERAL DEVICE CONFIGURATION. ON THE RIGHT: THE REAL CONFIG


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THE LATERAL CONFIGURATION. ON THE LEFT: SCHEMATIC VIEWTHE LATERAL CONFIGURATION. ON THE LEFT: SCHEMATIC VIEWLATERAL DEVICE CONFIGURATION. ON THE RIGHT: THE REAL CONFILATERAL DEVICE CONFIGURATION. ON THE RIGHT: THE REAL CONFIG

n the lateral conguration / t*o measuring electrodes/ > and A/ an the lateral conguration / t*o measuring electrodes/ > and A/ a

close together +elo* !"6he di0erence !D +et*een the spherical e4close together +elo* !"6he di0erence !D +et*een the spherical e4

surfaces on *hich > and A lie/ is derived as follo*s,surfaces on *hich > and A lie/ is derived as follo*s,

VVMMis the potential at electrode >/is the potential at electrode >/

VVNNis the potential at electrode A" So/ the potential di0erence isis the potential at electrode A" So/ the potential di0erence is


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THE CURRENT PATHTHE CURRENT PATH

6he resistivity measured is not e:actly that of the virgin formation 6he resistivity measured is not e:actly that of the virgin formation

is neither innite in e:tent/ nor homogeneous" Eeterogeneity is intis neither innite in e:tent/ nor homogeneous" Eeterogeneity is int

+y the presence of a 2uid-lled +orehole/ the invaded .one / and a+y the presence of a 2uid-lled +orehole/ the invaded .one / and a

formations in the sedimentary series"formations in the sedimentary series"

6he current traverses these .ones/ the e4uipotential surfaces are n6he current traverses these .ones/ the e4uipotential surfaces are n

spheres/ and e4s previously discussed are no longer strictly valid"spheres/ and e4s previously discussed are no longer strictly valid"


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THE CURRENT PATHTHE CURRENT PATH

! general relationship still holds/ *here,! general relationship still holds/ *here,,, is the apparenis the apparen

measured) resistivity= is e4ual to D for the normal array/ formeasured) resistivity= is e4ual to D for the normal array/ for

and inverse= and G is the geometrical coeHcient/ for the spacing aand inverse= and G is the geometrical coeHcient/ for the spacing a

conguration used"conguration used"

!fter correction for the e0ects of the +orehole for instance)/ a good!fter correction for the e0ects of the +orehole for instance)/ a good

appro:imation to R/ can +e made using the concept of the pseudo-appro:imation to R/ can +e made using the concept of the pseudo-geometrical factor ( 9 )/ considering the invaded and virgin .ones togeometrical factor ( 9 )/ considering the invaded and virgin .ones to

series electrically,series electrically,


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MEASURING POINT (DEPTH ZEROMEASURING POINT (DEPTH ZERO

The normalThe normal

6he depth reference point is taken at the middle of the spacing" or6he depth reference point is taken at the middle of the spacing" or

normal/ this corresponds to the mid-point of !>" 6hus for the 1'B annormal/ this corresponds to the mid-point of !>" 6hus for the 1'B an

normals/ *hich share a common ! electrode/ the measuring points dnormals/ *hich share a common ! electrode/ the measuring points d

is corrected optically on the lm"is corrected optically on the lm"

The lateral and inverse :The lateral and inverse :

6he measuring point is at 5/ the mid-point of >A (lateral) or !@ (inv6he measuring point is at 5/ the mid-point of >A (lateral) or !@ (inv


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RADIUS OF INVESTIGATIONRADIUS OF INVESTIGATION

The normal:The normal: n a homogeneous isotropic medium/ it is easy to sho*n a homogeneous isotropic medium/ it is easy to sho*of the potential drop to*ards .ero occurs *ithin a sphere of radius !of the potential drop to*ards .ero occurs *ithin a sphere of radius !

*ithin a radius 15 !>" So for the 1'B-normal/ only 15I of the signal *ithin a radius 15 !>" So for the 1'B-normal/ only 15I of the signal

from the formation +eyond 1'5B fromfrom the formation +eyond 1'5B from A.A.

6he radius of investigation (at *hich an ar+itrary &5I of the potent6he radius of investigation (at *hich an ar+itrary &5I of the potent

has occurred) is therefore e4ual to t*ice the spacing !> (ig)" Similahas occurred) is therefore e4ual to t*ice the spacing !> (ig)" Simila

vertical resolution is # !>"vertical resolution is # !>"


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RADIUS OF INVESTIGATION OF THE NORMAL A) THE ELECTRODE LRADIUS OF INVESTIGATION OF THE NORMAL A) THE ELECTRODE LIN THE WELL-BORE. B) THE CONTRIBUTIONS FROM THE VARIOUS ZOIN THE WELL-BORE. B) THE CONTRIBUTIONS FROM THE VARIOUS ZO

FUNCTION OF DISTANCE FROM THE SONDE AXISFUNCTION OF DISTANCE FROM THE SONDE AXIS


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RADIUS OF INVESTIGATIONRADIUS OF INVESTIGATION

Lateral and inverse:Lateral and inverse:6he radius of investigation of the lateral is6he radius of investigation of the lateral isappro:imately e4ual to !7/ *ith most of the signal deriving from thappro:imately e4ual to !7/ *ith most of the signal deriving from th

part of the sphere " or the inverse/ it is >7part of the sphere " or the inverse/ it is >7


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RADIUS OF INVESTIGATION OF THE LATERAL. A) THE ELECTRODE RADIUS OF INVESTIGATION OF THE LATERAL. A) THE ELECTRODE IN THE WELL-BORE. B) THE CONTRIBUTIONS FROM THE VARIOUS ZOIN THE WELL-BORE. B) THE CONTRIBUTIONS FROM THE VARIOUS ZO

FUNCTION OF DISTANCE FROM THE SONDE AXISFUNCTION OF DISTANCE FROM THE SONDE AXIS


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ENVIRONMENTAL CORRECTIONSENVIRONMENTAL CORRECTIONS


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THE SHAPE OF THE APPARENTTHE SHAPE OF THE APPARENTRESISTIVITY CURVERESISTIVITY CURVE

!s *ell as in2uencing the magnitude of the apparent resistivity/ the!s *ell as in2uencing the magnitude of the apparent resistivity/ theenvironmental factors discussed a+ove a0ect the shape of the log reenvironmental factors discussed a+ove a0ect the shape of the log re

a +ed of nite thickness"a +ed of nite thickness"


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THE NORMALTHE NORMAL

Thick resistive beds (hThick resistive beds (h JJAM)AM)

6he curve is symmetric a+out the middle of the +ed" Eo*ever/ the p6he curve is symmetric a+out the middle of the +ed" Eo*ever/ the p

in2ection (p and p) on the lo*er and upper slopes give an apparenin2ection (p and p) on the lo*er and upper slopes give an apparen

thickness shorter than true +y a distance e4ual to !>" 6he peak vathickness shorter than true +y a distance e4ual to !>" 6he peak va

*ill depend on +orehole and invasion e0ects (and/ to a lesser e:te*ill depend on +orehole and invasion e0ects (and/ to a lesser e:te

thickness unlessthickness unless hh JJ!>)"JJ!>)"


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THE NORMAL CONTD..THE NORMAL CONTD..

Thin resistive bedsThin resistive beds (h(h


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THE NORMAL CONTDTHE NORMAL CONTD

Very resistive thick bedsVery resistive thick beds (h(h JJAM)AM)

6his is the case of anhydrite/ salt or tight car+onate +eds" f referen6his is the case of anhydrite/ salt or tight car+onate +eds" f referen

electrode A is on the surface/ the response is a symmetrical +ell-shaelectrode A is on the surface/ the response is a symmetrical +ell-sha

do*nhole (on the +ridle/ 1B from >) the curve is triangular in formdo*nhole (on the +ridle/ 1B from >) the curve is triangular in form


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THE NORMAL CONTDTHE NORMAL CONTD

Conductive bedsConductive beds

!pparent +ed thickness (points of in2ection) is h K !>"6he response!pparent +ed thickness (points of in2ection) is h K !>"6he response

symmetrical " 6he thinner the +ed/ the harder it +ecomes to distingusymmetrical " 6he thinner the +ed/ the harder it +ecomes to distingu

the adFacent +eds"the adFacent +eds"

THELATERALANDINVERSETHELATERALANDINVERSE


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THE LATERAL AND INVERSETHE LATERAL AND INVERSE

Thick resistive beds (hThick resistive beds (h JJAO)AO)

6he curve is not at all symmetrical *ith respect to the +ed and can 6he curve is not at all symmetrical *ith respect to the +ed and can

several rather comple: forms " When > and A (lateral) enter the +edseveral rather comple: forms " When > and A (lateral) enter the +ed

)only a small di0erence of potential is measured +ecause most of th)only a small di0erence of potential is measured +ecause most of th

is re2ected into the adFacent shale" !s ! enters the +ed/ a resistivityis re2ected into the adFacent shale" !s ! enters the +ed/ a resistivity

4uite close to true value (allo*ing for +orehole and invasion e0ects)4uite close to true value (allo*ing for +orehole and invasion e0ects)

o+tained (.one #)" !s > and A leave the +ed/ the potential di0erenceo+tained (.one #)" !s > and A leave the +ed/ the potential di0erence

rapidly (after a small increase) to a value a little higher than that of trapidly (after a small increase) to a value a little higher than that of t

adFacent +ed (.one $)/ untiladFacent +ed (.one $)/ until AA has also passed through"has also passed through"

THELATERALANDINVERSETHELATERALANDINVERSE


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THE LATERAL AND INVERSETHE LATERAL AND INVERSEThin resistive beds (hThin resistive beds (h


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THE LATERAL AND NORMALTHE LATERAL AND NORMAL

Very resistive thick beds (hVery resistive thick beds (h JJJJAM)AM)

sho*s the unsymmetrical triangular response" the upper +oundary sho*s the unsymmetrical triangular response" the upper +oundary

displaced do*n*ards +y a distance e4ual todisplaced do*n*ards +y a distance e4ual to AOAO


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THE LATERAL AND NORMALTHE LATERAL AND NORMAL

Conductive bedsConductive beds

6he unsymmetrical response produces an apparent +ed thickness to6he unsymmetrical response produces an apparent +ed thickness to

a distancea distance A0A0


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NON-FOCUSING SHORT-SPACING TONON-FOCUSING SHORT-SPACING TO

6he kno*ledge of the resistivity of the 2ushed .one/6he kno*ledge of the resistivity of the 2ushed .one/ is important for seis important for sereasons" When the invasion of the reservoir is moderate to deep/ the kno*reasons" When the invasion of the reservoir is moderate to deep/ the kno*

allo*s the correction of the deep resistivity measurements for the in2uencallo*s the correction of the deep resistivity measurements for the in2uenc

invaded .one"invaded .one"

Some methods for computing *ater saturation re4uire the kno*ledge of tSome methods for computing *ater saturation re4uire the kno*ledge of t

ratio" n clean formation/ a computation of the formation factor/ratio" n clean formation/ a computation of the formation factor/ F,F, and conand con

of the porosity/of the porosity/ ,, can +e achieved fromcan +e achieved from kno*ing assuming tokno*ing assuming to

estimated or :ed to 155I"estimated or :ed to 155I"

6o measure the tool must have a very shallo* depth of investigation +6o measure the tool must have a very shallo* depth of investigation +

2ushed .one may e:tend only a fe* inches +eyond the +orehole *all" Sin2ushed .one may e:tend only a fe* inches +eyond the +orehole *all" Sinc

reading should not +e a0ected +y the +orehole mud/ a side*all-pad tool isreading should not +e a0ected +y the +orehole mud/ a side*all-pad tool is

PRINCIPLE OF NON FOCUSING SHORT SPACINGPRINCIPLE OF NON FOCUSING SHORT SPACING


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PRINCIPLE OF NON-FOCUSING SHORT-SPACING PRINCIPLE OF NON-FOCUSING SHORT-SPACING

6hree electrode-+uttons/ spaced 1 in" apart/ are mounted in line on6hree electrode-+uttons/ spaced 1 in" apart/ are mounted in line on

an oil-lled ru++er pad With these electrodes a 1in" +y 1in" micro-inan oil-lled ru++er pad With these electrodes a 1in" +y 1in" micro-in

aand a #-in" micro-normalnd a #-in" micro-normal recorded simultaneously"recorded simultaneously" AsAs drilling drilling

into the permea+le formations/ mud solids accumulate on the +oreinto the permea+le formations/ mud solids accumulate on the +ore

and form a mud-cake" sually/ the mud-cake resistivity is higher thand form a mud-cake" sually/ the mud-cake resistivity is higher th

resistivity +ut much lo*er than the 2ushed- or virgin-.one resistiviresistivity +ut much lo*er than the 2ushed- or virgin-.one resistivit

PRINCIPLE OF NON FOCUSING SHORT SPACING TOPRINCIPLE OF NON FOCUSING SHORT SPACING TO


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PRINCIPLE OF NON-FOCUSING SHORT-SPACING TOPRINCIPLE OF NON-FOCUSING SHORT-SPACING TO

6he pad-face is pressed against the +orehole *all either +y a hydr6he pad-face is pressed against the +orehole *all either +y a hydra

controlled spring pressure system in the oldest tools/ or +y a microcontrolled spring pressure system in the oldest tools/ or +y a micro

device such as microlaterolog or Pro:imity pad" Ae*er microresistdevice such as microlaterolog or Pro:imity pad" Ae*er microresisti

e4uipment of Schlum+erger includes a microlog tool and a >icroSe4uipment of Schlum+erger includes a microlog tool and a >icroSmodern tools/ the microlog can +e mounted on the po*ered calipemodern tools/ the microlog can +e mounted on the po*ered calipe

and run simultaneously *ith any com+ination logging devices, natand run simultaneously *ith any com+ination logging devices, nat

gamma-ray spectrometry/ litho-density/ neutron/ electromagnetismgamma-ray spectrometry/ litho-density/ neutron/ electromagnetism

vertical resolution is # to % in" for the micro-inverse/and % in" for thvertical resolution is # to % in" for the micro-inverse/and % in" for th

normal" 6he sampling rate is each # in" displacement"normal" 6he sampling rate is each # in" displacement"

ENVIRONMENTALEFFECTSENVIRONMENTALEFFECTS


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ENVIRONMENTAL EFFECTSENVIRONMENTAL EFFECTS f the pad is in perfect contact *ith the hole *all/f the pad is in perfect contact *ith the hole *all/

the +orehole 2uid has no e0ect on the reading"the +orehole 2uid has no e0ect on the reading"

Eo*ever/ these very shallo* measurements areEo*ever/ these very shallo* measurements are

very sensitive to the mud-cake/ across *hich thevery sensitive to the mud-cake/ across *hich thecurrent must 2o* opposite permea+le/ porous +eds"current must 2o* opposite permea+le/ porous +eds"

n rugose holes/ the pad makes irregular contact"n rugose holes/ the pad makes irregular contact"

6here may +e mud +et*een the electrodes and the6here may +e mud +et*een the electrodes and the

uneven *all of the hole/ causing erroneously lo*uneven *all of the hole/ causing erroneously lo*

measurements"measurements"

6he vertical denition is very ne/ and adFacent6he vertical denition is very ne/ and adFacent+eds *ill only a0ect the readings *hen +ed+eds *ill only a0ect the readings *hen +ed

thickness is less than a fe* inches"thickness is less than a fe* inches"

TOOL RESPONSETOOL RESPONSE


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OO S O S

n permea+le reservoirs/ as the #-in" micro-n permea+le reservoirs/ as the #-in" micro-

normal device has a greater depth ofnormal device has a greater depth of

investigation than the microinverse/ it is/investigation than the microinverse/ it is/

therefore/ less in2uenced +y the mud-cake"therefore/ less in2uenced +y the mud-cake"

When mud-cake is present/ andWhen mud-cake is present/ and ,,

the #-in" micronormal reads a higherthe #-in" micronormal reads a higher

resistivity/ *hich produces a distinctiveresistivity/ *hich produces a distinctive

MpositiveN curve separationMpositiveN curve separation *ith the*ith the

micro-inverse" 6hese MpositiveN separations aremicro-inverse" 6hese MpositiveN separations are

indicative of a porous permea+le .one " 6his isindicative of a porous permea+le .one " 6his is

+ecause the depths of investigation of the t*o+ecause the depths of investigation of the t*otools (and therefore the mud-cake e0ect) di0er"tools (and therefore the mud-cake e0ect) di0er"

Eo*ever/ negative separations *ill +e o+servedEo*ever/ negative separations *ill +e o+served

*hen*hen or *hen invasion is very shallo* (*ithor *hen invasion is very shallo* (*ith

TOOLRESPONSETOOLRESPONSE


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Shaly formationsShaly formations6here is generally no mud-cake/ and6here is generally no mud-cake/ and

the separation is negative"the separation is negative"


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6ight formations6ight formations

n impervious formations/ in the a+sence of mudcake and invasion/ tn impervious formations/ in the a+sence of mudcake and invasion/ t

micro-normal and micro-inverse curves are/ in principle/ measuringmicro-normal and micro-inverse curves are/ in principle/ measuring

R,.R,. Eo*ever/ the readings are very sensitive to the presence of muEo*ever/ the readings are very sensitive to the presence of mu

ssures/ ne conductive strata/ and poor application/ and any suchssures/ ne conductive strata/ and poor application/ and any such

anomalies *ill sho* up very clearly"anomalies *ill sho* up very clearly"

TOOLRESPONSETOOL RESPONSE


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TOOL RESPONSEOO S O S 6hey can sometimes e:hi+it some MnegativeN separation *ith muc6hey can sometimes e:hi+it some MnegativeN separation *ith muc

resistivities"resistivities" AA Mmud-logN *as usually recorded *hile running into tMmud-logN *as usually recorded *hile running into t

*ith the pad arms retracted" @oth measurements *ould Fump errat*ith the pad arms retracted" @oth measurements *ould Fump errat

the tool made intermittent contact *ith the hole *all on the *ay dthe tool made intermittent contact *ith the hole *all on the *ay d

minima on the shallo*-reading micro-inverse (corresponding to *hminima on the shallo*-reading micro-inverse (corresponding to *h

*as farthest from the *all) *ere taken as indicative of*as farthest from the *all) *ere taken as indicative of

FOCUSINGLONG-SPACINGTOOLSFOCUSINGLONG-SPACINGTOOLS


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FOCUSING LONG-SPACING TOOLSFOCUSING LONGSPACING TOOLS ocusing resistivity tools overcome/ to a greater or lesser e:tent/ theocusing resistivity tools overcome/ to a greater or lesser e:tent/ the

short-comings of the


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PRINCIPLEPRINCIPLE

t consists in forcing the currentt consists in forcing the current I,,I,, sent +ysent +y

the central electrodethe central electrode A,A, to penetrateto penetrate

perpendicularly into the formation +yperpendicularly into the formation +y

sending/ through symmetrically arrangedsending/ through symmetrically arrangedguard electrodes/ a focusing current"guard electrodes/ a focusing current"

6he guard electrodes emit focusing6he guard electrodes emit focusing

currents *hich constrain thecurrents *hich constrain the A,A, currentcurrent

+eam to 2o* perpendicularly out into the+eam to 2o* perpendicularly out into the

formation (the guard electrodes in factformation (the guard electrodes in fact

esta+lish e4uipotential surfaces coa:ialesta+lish e4uipotential surfaces coa:ial

*ith the tool/ forcing the*ith the tool/ forcing the A,A, current tocurrent toradiate perpendicularly to the a:is)"radiate perpendicularly to the a:is)" AsAs aa

result/ the +orehole and adFacent +edresult/ the +orehole and adFacent +ed

signals/ are considera+ly less than those ofsignals/ are considera+ly less than those of

the normals and laterals"the normals and laterals"

PRINCIPLEPRINCIPLE


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PRINCIPLEPRINCIPLE AllAll the currents return to an electrodethe currents return to an electrode

located far a*ay from !o"located far a*ay from !o"

Several devices/ +ased on this principle/Several devices/ +ased on this principle/

have +een +uilt and commerciali.ed +yhave +een +uilt and commerciali.ed +y

service companies " 6hey di0er +y theservice companies " 6hey di0er +y the

num+er of electrodes and their locationnum+er of electrodes and their location

or spacingor spacing

LATEROLOG3LATEROLOG3


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LATEROLOG 3LATEROLOG 3 6he LL$ device/ introduced +y Schlum+erger6he LL$ device/ introduced +y Schlum+erger

in 13&/ had three electrodes (ig" %-1$)"in 13&/ had three electrodes (ig" %-1$)" A,A, isis

the main current electrode/ *hich emits athe main current electrode/ *hich emits a

varia+le currentvaria+le current I,I, to a remote return"to a remote return" A,A, andand

A,A, are t*o long guard electrodes (a+outare t*o long guard electrodes (a+out 5-5- ft)/ft)/

connected together" 6heir potentialconnected together" 6heir potential VgVg isismaintained e4ual to an internal referencemaintained e4ual to an internal reference

potentialpotential V,V, +y a self-adFusting +ucking current+y a self-adFusting +ucking current

ZgZg *hich 2o*s from*hich 2o*s from A,-A',.A,-A',.6he potential6he potential V,V, ofof

A,A, *as held e4ual to*as held e4ual to VgVg +y varying the main+y varying the main

currentcurrent I,.I,. Al-&-A,Al-&-A, *as thus an e4uipotential*as thus an e4uipotential

surface/ and currentsurface/ and current I,I, could only 2o* outcould only 2o* out

perpendicularly/ as a disc of thicknessperpendicularly/ as a disc of thickness 0-0.0-0.66

he magnitude of Oo *as measured= it *ashe magnitude of Oo *as measured= it *as

proportional to the formation conductivity/proportional to the formation conductivity/since,since, Unfo!sedUnfo!sed

!Vo!Vo ;; RloRlo so that,so that,

I,I, ;; !V,",!V,", *here C is the conductivity"*here C is the conductivity"

DRAWBACKSOFLL3DRAWBACKSOFLL3


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DRAWBACKS OF LL3DRAWBACKS OF LL3

6he LL$ tool had certain dra*+acks" 6he current tended to esca6he LL$ tool had certain dra*+acks" 6he current tended to esca

either into the more conductive surrounding shoulder" 6his is theeither into the more conductive surrounding shoulder" 6his is the

reason *hy it *as replaced +y other devices"reason *hy it *as replaced +y other devices"

DRAWBACKSOFLL3DRAWBACKSOFLL3


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DRAWBACKS OF LL3DRAWBACKS OF LL3

6he LL$ tool had certain dra*+acks" 6he current tended to escape into6he LL$ tool had certain dra*+acks" 6he current tended to escape into

intercalated conductive layer " 6his is the reason *hy it *as replaced +intercalated conductive layer " 6his is the reason *hy it *as replaced +

devices"devices"


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LL7LL7

6he LL device/ introduced +y Schlum+erger in 13&/comprised a 6he LL device/ introduced +y Schlum+erger in 13&/comprised a

electrodeelectrode Ao,Ao, and three pairs of electrodes, >1 and >#and three pairs of electrodes, >1 and >#"" >1/ and>1/ and ##

A%A% andand A',A',


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LL7LL7

6his is a shallo*-reading laterolog/ similar in design to/6his is a shallo*-reading laterolog/ similar in design to/

the laterologthe laterolog ,, e:cept that the spacings are smaller/ ande:cept that the spacings are smaller/ and

the current returns are much closer" 6he thickness of thethe current returns are much closer" 6he thickness of the

I,I, current sheet iscurrent sheet is %% in"/ and the distance +et*een thein"/ and the distance +et*een the

t*o +ucking electrodes is some*hat less thant*o +ucking electrodes is some*hat less than 00 in" 6hein" 6he

return current is located a relatively short distance fromreturn current is located a relatively short distance from

!/" 6he spacing factor (!4!/515#) *as e4ual to $" 6his!/" 6he spacing factor (!4!/515#) *as e4ual to $" 6his

sonde *as com+ined *ith the dual induction QL (6i:ier etsonde *as com+ined *ith the dual induction QL (6i:ier eta#.,a#., %()5*.%()5*. ts pseudo-geometrical factor is reproduced ints pseudo-geometrical factor is reproduced in

!dFacent graph!dFacent graph


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DUAL INDUCTION LOGDUAL INDUCTION LOG

ENVIRONMENTAL CORRECTIONSENVIRONMENTAL CORRECTIONS


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6he measured apparent resistivity6he measured apparent resistivity R,R, is a function of a num+er of dis a function of a num+er of d

parameters,parameters,

6he apparent resistivity (Ra)c o+tained +y correcting for the +oreh6he apparent resistivity (Ra)c o+tained +y correcting for the +oreh

adFacent +eds / is related to the true R/ +y,adFacent +eds / is related to the true R/ +y,

FOCUSINGSHORT-SPACINGMICRO-RESISFOCUSINGSHORT-SPACINGMICRO-RESIS


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FOCUSING SHORT-SPACING MICRO-RESISFOCUSING SHORTSPACING MICRORESISTOOLSTOOLS

n order to reduce the +orehole e0ect on shallo* depth of investign order to reduce the +orehole e0ect on shallo* depth of investiga

services companies have developed several types of tools +ased oservices companies have developed several types of tools +ased o

same fundamental conguration (6a+le %-$)" 7ne *ill descri+e thesame fundamental conguration (6a+le %-$)" 7ne *ill descri+e the

Schlum+erger tools/ the other tools +eing very similar in their concSchlum+erger tools/ the other tools +eing very similar in their conc

MICROLATEROLOG-MLLMICROLATEROLOG-MLL


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PrinciplePrinciple

6he principle of measurement is the same as that of the LL-" 6he el6he principle of measurement is the same as that of the LL-" 6he el

array is mounted on an oil-lled ru++er pad/ as sho*n +elo*" 6he cearray is mounted on an oil-lled ru++er pad/ as sho*n +elo*" 6he ce

electrode is surrounded +y three concentric rings of +uttons/ constitelectrode is surrounded +y three concentric rings of +uttons/ constitu

>/ >/ and>/ >/ and A,,A,, electrode rings respectively" (6his amounts to a circulelectrode rings respectively" (6his amounts to a circula

array/ in fact")array/ in fact")



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#eas!ring +oint#eas!ring +oint,,

6he measuring point is at6he measuring point is at A,.A,.6he spacing is the diameter of a circle 6he spacing is the diameter of a circle

mid-*ay +et*een > and >/"Dertical denition is a+out 1"B" Qepth ofmid-*ay +et*een > and >/"Dertical denition is a+out 1"B" Qepth of

investigation is 1 -#B"investigation is 1 -#B"

nvironmental eetsnvironmental eets,,

We can ignore the +orehole and mud in2uence provided that pad contaWe can ignore the +orehole and mud in2uence provided that pad conta

#!d-ae in/!ene:#!d-ae in/!ene:

6he mud-cake/ ho*ever/ cannot +e ignored" 6he chart of igure %-& is6he mud-cake/ ho*ever/ cannot +e ignored" 6he chart of igure %-& is

correct R>LL for mud cake thickness and resistivity" (R>L9c should +ecorrect R>LL for mud cake thickness and resistivity" (R>L9c should +e

R//" 6he greater the value of R// R/// the greater the tendency for the R//" 6he greater the value of R// R/// the greater the tendency for the

escape through the mud-cake to the mud in the +orehole"escape through the mud-cake to the mud in the +orehole"



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ed thiness in/!eneed thiness in/!ene,,

or +eds thicker than 1"B/ adFacent +eds have no apprecia+le e0ector +eds thicker than 1"B/ adFacent +eds have no apprecia+le e0ect



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1nvasion in/!ene:1nvasion in/!ene:

6he virgin .one does not e0ect if6he virgin .one does not e0ect if

invasion is deeper than a fe* inches" Deryinvasion is deeper than a fe* inches" Dery

shallo* invasion *ill produce a readingshallo* invasion *ill produce a reading

some*here +et*een R// and R/" n thissome*here +et*een R// and R/" n this

case/ *e can compute R/ +y com+iningcase/ *e can compute R/ +y com+ining

several di0erent resistivity measurements/several di0erent resistivity measurements/

and using the step prole model"and using the step prole model"

MUD-CAKE CORRECTION FACTORMUD-CAKE CORRECTION FACTOR


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THE PROXIMITY LOG (PL)THE PROXIMITY LOG (PL)


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Principl:Principl:

This type of device works on the sameThis type of device works on the same

principle as the -3, but uses rectangularprinciple as the -3, but uses rectangularelectrodes with a common center (*ig. 4-electrodes with a common center (*ig. 4-

56), mounted on a solid rubber pad, wider56), mounted on a solid rubber pad, wider

than the pad. The system isthan the pad. The system is

automatically focused by monitoringautomatically focused by monitoring

electrodes. Its vertical resolution is about 5electrodes. Its vertical resolution is about 5

in. #orrections for shoulder bed influencein. #orrections for shoulder bed influencemust be achieved if the bed thickness ismust be achieved if the bed thickness is

smaller than 7 footsmaller than 7 foot

THE MICROSFL (MSFL)THE MICROSFL (MSFL)


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0rinciple0rinciple

This is a small-scale * array, mounted on a fle8ibleThis is a small-scale * array, mounted on a fle8ible

rubber pad. It has two advantages over the andrubber pad. It has two advantages over the and

0202

- it is less sensitive to the mud-cake than the , and- it is less sensitive to the mud-cake than the , and

reads shallower than the 0 9reads shallower than the 0 9

- it can be combined with other tools, such as the - it can be combined with other tools, such as the

and I, while the or 0 re:uire a separate runand I, while the or 0 re:uire a separate run

(and therefore more rig-time, and risk of sticking).(and therefore more rig-time, and risk of sticking).

ynthetic microlog curves can be computed from *ynthetic microlog curves can be computed from *

parameters. ince the measure current sees mostlyparameters. ince the measure current sees mostlythe flushed ;one and the bucking current seesthe flushed ;one and the bucking current sees

primarily the mud-cake, it is possible to mathematicallyprimarily the mud-cake, it is possible to mathematically

derive a micro-normal and a micro-inverse curves.derive a micro-normal and a micro-inverse curves.

FACFACTORS INFLUENCING THE RESISTIVITYTORS INFLUENCING THE RESISTIVITYMEASUREMENTSMEASUREMENTS


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En!ir"n#n$%l &&c$'

G"l"(ic%l &%c$"r' in&l)ncin( r'i'$i!i$*

%ock composition%ock composition

%ock te8ture%ock te8ture

-Tortuosity-Tortuosity

-permeability-permeability

-microscopic anisotropy-microscopic anisotropy

ipsips *ractures*ractures

edimentarv structure, facies, depositional environnent,edimentarv structure, facies, depositional environnent,the geological se:uethe geological se:ue

FACTORS INFLUENCING THE RESISTIVITYFACTORS INFLUENCING THE RESISTIVITYMEASUREMENTSMEASUREMENTS


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6emperature6emperature

Pressure-CompactionPressure-Compaction

SUMMARYSUMMARY Resistivity loggingResistivity logging


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y gg gy gg g

>easurement of resistivity>easurement of resistivity

6echni4ues used to measure resistivity6echni4ues used to measure resistivity

unction of spacing value and considering categories of tools"unction of spacing value and considering categories of tools" Why com+ination of these tools is important?Why com+ination of these tools is important?

>easuring point>easuring point

Aon focused long spacingAon focused long spacing

Aon focused short spacingAon focused short spacing

ocused long spacingocused long spacing

ocused short spacingocused short spacing

actors in2uencing the resistivity measurements"actors in2uencing the resistivity measurements"

5a. resistivity logging

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