Environmental Engineering Reference
In-Depth Information
For example, in a shale, GR = 110 and ˕
T
= 33 %; but, in a clean section, GR = 25 and
˕
T
= 25 %, so it follows that:
GR
dc
= 110/(1 − 0.33) = 149.25, and
GR
ma
= 25/(1 − 0.25) = 33.3.
Finding
˕
T
and
V
dc
As already stated, ˕
T
is found from the ʣ vs. ratio crossplot.
V
dc
can be found from
the
GR
using:
(
)
GR GR
GR
-
1 f
-
ma
T
V
dc
=
-
GR
dc
ma
Solving for
˕
e
and
S
we
Once
V
dc
and ˕
T
are established, the following relationships hold:
˕
e
= ˕
T
-
V
wb
(which also =
V
hy
+
V
wf
),
V
ma
= 1 − ˕
T
-
V
dc
, and
V
wb
= ʱ
V
dc
,
where ʱ has been established in the shales as ˕
Ts
h
/(1 − ˕
Tsh
).
The response of the pulsed neutron log itself can be written as:
SS S
=
V
+
V
+
S aS S
V
+
V
+
V
,
ma ma
dc
dc
wb
dc
wf wf
hy
hy
hence:
(
- .
The right side of the equation can be evaluated since all the parameters and variables
have now been deined. If this quantity is, in fact, ʣ*, then
S
V
+
S SS S S
V
=
-
VV
+
hy
hy
wf wf
ma ma
dc
dc
wb
*
SfS
SS
-
e y
V
wf
=
-
wf
hy
By definition,
SV
we
= /f
wf
e
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