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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