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PetrophysicsMScCourseNotes WirelineLogging
5. WIRELINELOGGING
5.1 Whatisa WirelineLog
A log is a continuous recording of a
geophysicalparameteralongaborehole.
Wireline logging is a conventional form of
logging that employs a measurement tool
suspended on a cable or wire that suspends
the tool and carries the data back to the
surface. These logs are taken between
drilling episodes and at the end of drilling.
Recent developments also allow some
measurements to be made during drilling.
The tools required to make these
measurementsareattached to thedrillstring
behind thebit, and do notuseawirerelying
instead on low band-width radio
communication of data through the
conductivedrillingmud. Suchdataiscalled
MWD (measurement while drilling) for
simple drilling data, and LWD (logging
while drilling) for measurements analogous
to conventional wireline measurements.
MWDand LWDwillnotbecovered bythis
course, although the logs that are produced
inthiswayhaveverysimilarcharacteristics,
even though they have been obtained in a
completelydifferentway.
Figure 5.1 shows a typical wireline log. In
thiscaseitisalogthatrepresentsthenatural
gamma radioactivity of a formation. Note
that depth is arranged vertically in feet or
metres, and theheadercontainsthenameof
the log curve and the range. This example
showsasingletrackofdata. Notealso that
no data symbols are shown on the curve.
Symbols are retained to represent discrete
core data by convention, while continuous
measurements, suchaslogs, arerepresented
bysmoothcurves. Figure5.1 showsonly50
mofborehole, butreallogsareoftenmuch
longer (thousands of metres), and contain
multiple curves on a single track such as
this, and multipletracks.
Fig. 5.1 ExampleofaGammaRayLog
GAMMARAY(GR)
1000
630
620
APIUNITS
640
670
660
650
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PetrophysicsMScCourseNotes WirelineLogging
Figure5.2 Atypicallogset
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PetrophysicsMScCourseNotes WirelineLogging
Figure5.3 Land loggingvehicle
Figure5.4 Offshoreloggingcabin
Figure5.5 Insidetheloggingunit
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PetrophysicsMScCourseNotes WirelineLogging
Datais transmitted to thesurface through the wireand recorded digitally. Modern toolssample the
formation at intervals from 2.5 mm for the high definition imaging tools to about 15 cm for the
simplertools, so foracombinationtoolwithseveraldifferentlogs, theremaybeasmanyas100,000
individual measurements per metre over a log run ofup to say2000 m. Depending on the logging
speed, data transmission rates may be as high as 200 kbits per second. This data is subjected
immediatelyto arudimentaryanalysisbypowerfulprocessorsand displayed so thatthequalityofthemeasurementscanbechecked. Thedataisalso recorded onto digital(DAT)tapeand transmitted to the
controllingofficeoftheloggingcompanybysatelliteforin-depthanalysis.
Atypicaldrillingand logginghistoryforawellmightbeasshowninTable5.1. Notethatthelogsare
runineachsectionbeforecasingtakesplace. Wheneachlogisrun, theoperatorensuresthatsome
measurementsareincluded oppositethepreviouslycased sectionabovethelogrunasatestthatthe
logtoolsareworkingcorrectlyand to providealocaldepthfixed pointto help tiethedepthsforeach
tool together. Whenever a borehole is logged in sections the operator also ensures that there are
overlap sections so that the logs can be tied together accurately, and repeat sections to check log
qualityand consistency.
Table5.1 Atypicaldrillingand logginghistory.
Procedure DrillBitSize
(inches)
Casing Diameter
(inches)
Depth
(msubsea
surface)
Tools
Drill 25 - 300-400
Case 20 300-400
Drill 17.5 - 400-700
Log - - 700-400 ISF-Sonic-GR/1
Case
-
13.375 300-
690Drill 12.25 - 700-1400
Log - - 1400-680 ISF-Sonic-GR/2
Log - - 1400-680 FDC-CN L/1
Log - - 1400-680 HDT/1
Case - 9.625 690-1390
Drill 8.5 - 1400-2100
Log - - 2100-1380 ISF-Sonic-GR/3
Log - - 2100-1380 FDC-CN L/2
Log - - 2100-1380 HDT/2
Log - - 2100-1380 DLL/1
NoteinTable5.1 thatthelogsarerecorded duringthewithdrawalofthetoolsfromthewell, thatsome
tools were run several times at different depth intervals and that these runs have been coded
consecutively, thatthereisanoverlap ofdata, and thatthelowerlogrunsincludepartoftheprevious
casingattheirtop. Notealso thatthemosttoolsarerunintheareathatisexpected to beofgreatest
interest(i.e., thereservoir). Fortoolcodesseewirelineoperatorsmanuals.
Effortsaremadeatalltimesto ensurethatthelogsareofthehighestquality. Methodsofensuringthat
loggingqualityishighinclude(a)makingrepeatsectionsoflogmeasurementsovershortsectionsthat
contain both low and high measured values, (b) making overlap measurements of the previous
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PetrophysicsMScCourseNotes WirelineLogging
Figure5.6 Logpresentationgrids. NotethattheAPIformatdefinesparticulardimensionsforeach
track, and anoverallwidthof8.25 inches.
5.4 Tools
There are a plethora of logging toolsnow available in the oil industry. There can be split into the
followingtypes:
Standardopen-holetools(diameter3 to 4 inches)
Theserangefromthesimplestcalipertoolto thesophisticated imagingand NMRtoolsand have
verticalresolutionsfrom2.5 mmto over30 cm.
Slimholetools(diameter1.6875 to 2 inches)
Theseareslimmerversionsofthestandard tools, and areused wherestandard toolsaretoo thick.
Applicationsofthesetoolsareinspecialistloggingthroughdrill-pipeorcoiled tubing, and in
smallscaleholesused inthewaterindustry.
0 10
3600
361010 200 10
Track1 Track3Track2Depth
0 10
3600
3610100 10001 10
0 10
3600
36100 101 10
Linear
Logarithmic
Hy
brid
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PetrophysicsMScCourseNotes WirelineLogging
Cement-logging tools
Thesearespecialversionsofthosetoolsthatwork throughcementcasingthatareoptimized to
work undertheseconditions.
Productiontools
Thesearespecialisttoolsforrunningduringtheproductionofhydrocarbonsformeasuring
pressureand flowrate, and arealwaysoftheslim-holevarietyto facilitatetheirinsertioninto aproducingwell.
LWDtools
Thesetoolsaredesigned to connectinto thedrillstringand communicatedatato thesurface
throughthedrillingmud.
Asummaryofsomeofthemainstandard open-holetoolsisgiveninTable5.2.
Drillingrigsareexpensiveand canoftenamount to almost10%ofthe totaldrillingcosts. The time
required to runwirelinelogseffectivelydelays thedrillingoperationleading to greaterexpense. To
minimizethisexpensetoolsarebolted togetherforloweringdowntheborehole. Allwirelinetoolsare
designed to becombined in this wayand therearemanypossiblecombinations, somewhichareas
longas30 m. Eachtoolinthecombinationhasitsownmeasurement-sensitiveregion, whichmeasures
agiven formation at a specific depth at different offset times. The datahas to be depth shifted to
accountforthis. Thisisdoneinthedataacquisitionvehiclewithinformationabouttheinstantaneous
speed and dimensionsofthetoolcombination. Evenusingcombinations, itiscommonforasmanyas
threelogrunsto bemadeinthesamesectionoftheboreholewithdifferentcombinationsoftools. If
thisisthecase, onetoolisincluded inallcombinationsto actasareferenceto whichtheothersmight
becompared fordepthmatchingpurposes. Thistooliscommonlythegammaraytool(GR).
Figure5.7 showsanexamplestandard open-holeloggingtool. Notethatitisaneutronporositytool,
whichiscombined withagammaraytool. Theloopsateachend coverscrewthreadsto enableitto be
combined withothertoolsofsimilardesign.
Onland, wherethegeneralgeologyiswellknownand drillingischeaper, onlyafewlogsmayberun.
Thisisbecauseexpensecanbespared asinformationconcerningthesubsurfaceisnothard to come
by. However, and perhapscounter-intuitively, offshoreafullsetoflogsisoftencarried outevenwhen
there areno hydrocarbonshows. Thisisbecausedrillingisso expensive that relativelyfewerwells
willbedrilled, and hencethemaximumdatamustbesqueezed outofeachwellregardlessalmostof
thecost. Ifthereareno hydrocarbonshows, thewelldatawillstillbeveryusefulforcorrelationwith
otherwellsthatdo showhydrocarbons, willhelp to constraintheextentofneighbouringreservoirs, as
wellasaddingto theinformationaboutthegeneralgeologicalstructureofthearea.
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PetrophysicsMScCourseNotes WirelineLogging
Figure5.7ACompensated NeutronSonde(CNS)
Length 3.87 m(12.68 ft)
Diameter 95 mm(3.74 in)
Weightinair 109 kg(240 lb)
Range-3 to 100
lpu
Resolution Betterthan0.05 puat20 pu
Vert. Resolution 750 mm(30 in)
InvestigationDepth 260 mm(10.2 in)
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PetrophysicsMScCourseNotes WirelineLogging
Table5.2 Commonopen-holetoolsand theiruses
Tool PhysicalMeasurement Use Comments
Logging conditions
Temperature(BHT)
Pressure(PRESS)
Caliper(CAL)
Temperature
Fluid pressure
Boreholediameter
Boreholetemperatureforresistivity
calculations.
Fluid pressureforformationvolume
factorcalculations.
Dataquality, insitustresstensor,
lithologyand permeabilityindicator
Corrected withHornerplot
Incorporated inRFT
Availablein2, 4, ormulti-
armversions.
Lithology
GammaRay(GR)
Spontaneous
Potential(SP)
Naturalradioactivityof
theformation.
Sand/shaleinterface
potential.
Shaleindicatorand depthmatching
Permeablebeds
Resistivityofformationwater
Canread throughcasing.
Doesnotwork inconductive
muds, oroffshore.
Porosity
Sonic(BHC, LSS)
Density(FDC,
LDT)
Neutron(SNP,
CN L)
Velocityofanelastic
waveintheformation.
Bulk densityofthe
formation.
Hydrogenconcentration
intheformation.
Effective(connected)porosity
Totalporosity
Totalporosity(shaleincreases
measured porosity, gasreduces
measured porosity)
Compaction, gasand vugs,
calibrationofseismicdata.
Used to calculatesynthetic
seismograms.
Canread throughcasing.
Resistivity
Simpleelectriclog
(SN, LN, Lat)
InductionLogs
(IES, ISF, DIL,
DISF, ILm, ILd)
Laterologs
(LL3, LL7, DLL,
LLs, LLd)
Microlog(ML)
Micro-laterolog
(MLL)
ProximityLog(PL)
Micro-spherically
focussed log
(MSFL)
Resistivityofflushed,
shallowand deep zones
respectively.
Conductivityofthe
formation.
Resistivityofthe
formation.
Resistivityofmudcake
and flushed zone.
Resistivityofflushed
zone.
Resistivityofflushed
zone.
Resistivityofflushed
zone.
Used inwatersaturationcalculations.
Conductivityand resistivityinoil
based muds, and hencecalculationof
watersaturation.
Resistivityinwaterbased muds, and
hencecalculationofwatersaturation.
Indicatorofpermeability.
Detectorofthinbeds.
MeasuresRXO
MeasuresRXO
MeasuresRXO
Nowobsolete, notfocussed,
cantbeused inoilbased
muds, proneto invasion.
Focussed devices.
Useinoilbased and fresh
watermuds. Rangeofdepths
ofinvestigation. (Vertical
resolution5-10 ft.)
Focussed devices.
Useinsaltwaterbased
muds. Rangeofdepthsof
investigation. (Vertical
resolution2-4 ft.)
(verticalresolutionabout1
ft.)
Notgood withthick
mudcakes.
Notgood ifinvasionis
small.
PartofDLL-RXOtool.
Imaging Logs Thereisarangeofimaginglogsbased uponsonic, visual, electricaland NMRmeasurementsthatare
beyond thescopeofthiscourse.
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