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7/27/2019 Gamma Ray and Gamma Ray Absorption Logs
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Units
Decayratesan a i e
Naturalgammaradiationasshaleindicator
Gammarayabsorption
Elasticandinelasticneutronscattering
7/27/2019 Gamma Ray and Gamma Ray Absorption Logs
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GammaRay
and
GammaRa Absor tion
Logs
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BassiouniCh.7GammaRayLog
BassiouniCh.8GammaRayAbsorptionLogs
Liu,C(Richard),UH(API)NuclearLoggingCalibrationFacilityPowerPointpresentation
J.S.WahllJ.TittmanlC,W.Johnstone,TheDualSpacingFormationDensityLog,,JPT1964
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.
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Detectors
GeigerMuellertube
Proportionalcounter
ScintillationcounterThalliumiodidedopant
em ts or ue g t
Fastandefficient
byspring
raysscattermultiple
timesscatterbefore
reachingthedetector
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AveragingEffectson
ApparentGammaRayIntensity
Electronicaveragingindetector
Loggingspee
Toollength
Othernecessarycorrections
Eccentricity
as ngan cemen presen
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AveragingofStatisticalVariations
andEffectonLoggingSpeed
decay
statisticalvariationhasnothingtodowith
formationevaluation
Toproduceaninterpretablelog,weaverageoutthestatisticalvariationselectronically
Theelectronicaveraginghasasideeffectonloggingspeed
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Open
Circuit,i.e.,
Pulses
veryhigh
impedance
single-charge pulses per secondJ
e ec r c c arge
inI JQ
VI
At steady state soin out
RI I
V JQR
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imposesanupperlimitonloggingspeed
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ShaleEstimation shmin
from
GammaRa Lo s
logAssumethelog
,
correctionforknown
effects,islinearly
proportionaltothe
amountofshale
log min
min
sh
sh
I
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or
itcou come romsan stone orot er roc s
withunusuallyhighamountsofradioactivem nera s euran um.
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energyaswell
Approximationschemeforquick
calculationof
elementallogs
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Assumetotal
response sa
linear
superposition
Th,U,K
Also
GRS=Th+K=
uran um ree
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Inbothsandstone
andshale
Wewouldnaively
interpretasshale
wou n we~3Xinshales
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RuleofThumbCalculation
ofSpectralComponents
For Schlumber er devices
(API units) 4 ( ) 8 ( ) 16 (% )Th U K C ppm C ppm C wt
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ActivesourceofgammaraysCs137 orCo60
U timate ywe etectgammaraya sorption
bythephotoelectriceffectwhichdependsont enum ero ava a ee ectrons
0e peN xI I e
number of electrons per unit volume
cross section for hotoelectric effect
e
where
N
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path
effects
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somewhatfor
MudcakeThickness
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