Geology Reference
In-Depth Information
0.8
0.8
0.6
0.6
0.4
0.4
δ
ε
0.2
0.2
0
0
-0.2
-0.2
-0.4
-0.4
-0.4
-0.2
0
0.2
0.4
0.5
0.6
-0.4
-0.2
0
0.2
0.4
0.5
0.6
ε
γ
Figure 5.40
Crossplots of vertical polar anisotropy parameters listed by Thomsen (
1986
), Vernik and Liu (
1997
) and Ryan-Grigor (
1997
).
0.3
Intrinsic
Crack induced Dry
Crack induced Wet
0.5
0.2
δ=ε
0.1
0.4
lms
sh
ss
0
0.3
-0.1
-0.2
0.2
-0.3
0.1
-0.4
-0.1
0
0.1
0.2
0.3
0.4
0
ε
-0.1
Figure 5.41
V
p
/
V
s
vs
δ
crossplot based on data selected by Ryan-
Grigor (
1997
).
-0.2
0
0.1
0.2
0.3
0.4
0.5
0.6
2
h
C
44
i
2
V
s
2
V
p
C
13
1
þ
1
ε
δ ¼
:
ð
5
:
7
Þ
V
s
2
V
s
2
Figure 5.42
intrinsic anisotropy
is inferred from data at high confining pressure of 70 MPa and crack
induced anisotropy is inferred from data at low confining pressure
(after Vernik and Liu,
1997
).
Data for
ε
and
δ
for black shales
-
V
p
V
p
2
1
Effectively, at small to moderate angles of incidence
it is the difference in
the interface respectively. When
is negative the
gradient is made more negative by the anisotropic
contribution. Conversely, when
Δδ
across the boundary that is
the controlling factor in the effect of (vertical)
polar anisotropy on the AVO response (Banik,
1987
).
δ
is positive the
gradient is made more positive. The observation
that
Δδ
δ
2
are the delta values on the upper and lower sides of
Δδ
δ
2
δ
1
,where
δ
1
and
is defined as
δ
is most likely to be positive in shales and
86
