Geology Reference
In-Depth Information
a)
b)
7500
Sand, Shaley San
d
Shale, Sandy Shale
7000
Shaley sand
6500
Sandy
shale
6000
Sand
5500
5000
Shale
4500
4000
0.0
0.1
0.2
0.3
0.4
s
s
Porosity
c)
d)
0.2
0.5
Shale
Shale
Shale
Shale
Sandy
shale
Sandy
shale
Sandy
shale
Sandy
shale
0.1
0.4
Shale
0.0
Sand
Sand
Sand
0.3
Shaley sand
Shaley sand
Shaley sand
-0.1
Sandy
shale
0.2
-0.2
Shaley sand
0.1
-0.3
0.0
-0.4
0.0
0.1
0.2
0.3
0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
Porosity
Intercept
Figure 5.21
The effect of dispersed shale on sandstone properties; (a) schematic illustration of sand/shale mixtures (note that c
¼
clay
content and
s ratio plot, (d) AVO crossplot. Note that these figures relate to
experimental results with coarse quartz grains and fine kaolinite powder at an effective pressure of 40 MPa (modified after Marion
ϕ
s
¼
sand porosity), (b) porosity vs
AI
plot, (c) porosity vs Poisson
'
et al
.,
1992
).
a)
b)
N_D_diff
N_D_diff
2.7
0.3
0.5
0.3
2.6
0.25
0.25
0.4
0.2
2.5
0.2
0.3
0.15
2.4
0.15
0.2
0.1
2.3
0.1
0.1
0.05
2.2
0.05
0
2.1
0
0
60
70
80
DT (
μ
s/ft)
90
100
110
0
0.1
0.2
0.3
Porosity
Figure 5.22
An example of the effect of dispersed shales in a Jurassic deltaic sequence. Note colour coding is the difference between
neutron porosity and density porosity, a good indicator of clay content in sandstones (Katahara,
2008
); (a) sonic slowness vs density plot, (b)
density porosity vs Poisson's ratio plot.
73
