2. Introduction
Shale is usually more radioactive than sand or carbonate, gamma ray log can
be used to calculate volume of shale in porous reservoirs. The volume of shale
expressed as a decimal fraction or percentage is called Vshale.
Calculation of the gamma ray index is the first step needed to determine the
volume of shale from gamma ray log.
All of the prs files are available in the LogMath section of the Hampson-Russell
Knowledgebase for copying and pasting into the LogMath window.
3. Various Equation for Vshale Calculation
The gamma ray log has several nonlinear empirical responses as well a linear
responses. The non linear responses are based on geographic area or formation age.
All non linear relationships are more optimistic that is they produce a shale volume
value lower than that from the linear equation.
min
max
min
log
GR
GR
GR
GR
I
V GR
sh
−
−
=
=
Linear response (Vshale = IGR) :
Vshale_linear.prs
4. Various Equation for V shale Calculation
The nonlinear responses are :
• Larionov (1969) for older rock :
• Clavier (1971) :
• Steiber (1970) :
• Larionov (1969) for Tertiary rocks :
)
1
2
(
083
.
0 7
.
3
−
= GR
I
sh
V
GR
GR
sh
I
I
V
×
−
=
2
3
[ ]2
1
2
)
7
.
0
(
38
.
3
(
7
.
1 +
−
−
= GR
sh I
V
)
1
2
(
33
.
0 2
−
×
= GR
I
sh
V
Vshale_Larionov_Tertiary_Rock.prs
Vshale_Steiber.prs
Vshale_Clavier.prs
Vshale_Larionov_Older_Rock.prs
