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7/31/2019 Petrophysics - Gamma Ray
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Measures naturally occurring gamma rays.
The three most common isotopes are:
Potassium (K)Thorium (Th)
Uranium (U)
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Principle of Measurement
Measures Total Scintillation Response to Natural Gamma Radiation Emitted bythe Formation
Measures Spectral Scintillation Response of Natural Gamma Ray Emitters (K, U,Th)
Uses
Shale Volume
Correlation
Well to Well, Open Hole to Cased Hole
Lithology Identification
Combinable with nearly all other Logging Tools
Clay Typing
Uranium-corrected GR Curve
CLSH
CL
SHGRGR
GRGR
V
=
log
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1.46 MeV 2.62 MeV
1.76 MeV
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Potassium, %
21 3 4 500
4
8
12
16
20
Thorium,ppm
heavy Thminerals
illite
micas
glauconite
feldspars
potassium evaporites
mixedlayer clays
montmorillonite
28 Th/K = 12
3.5
0.8
0.5
0.6
2
1 10 100
Th/K ratio x 104
K-feldspar
glauconite
illite, muscovite
mixed layer clays(illite-montmorillonite)
kaolinite/chlorite
bauxite
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Which Curve is Gamma Ray?
Gamma Ray