Gamma Ray and Gamma Ray Absorption Logs

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Units

Decayratesan a i e

Naturalgammaradiationasshaleindicator

Gammarayabsorption

Elasticandinelasticneutronscattering

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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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