Geology Reference
In-Depth Information
Porosity, %
0
2
4
6
8
10 12
14
16
18
20
22 24
26
28
30
32
34
36
38
40 42
44
500
1000
2000
3000
4000
5000
6000
7000
H,
m
Figure 5.7
Clay porosity vs. depth.
1.
Central Apsheron,
2.
Baku Archipelago.
subsidence depth, which facilitates the preservation of high
shale porosity at great depths.
3. The clay compaction rate in alternating sand-clay deposits is
much higher than in the same-age mostly clayey sequences.
In the latter case, clay porosity (water-saturation) stabiliza-
tion occurs at high porosity values (10 to 12%), which cor-
responds with the 2 to 2.5 km burial depths in the sand-clay
alternation areas.
4. In all regions, clay compaction rates decline substantially
with depth. This indicates a tendency toward substantial
decrease in the outflow rate and the amount of squeezed-out
fluids at great depths.
5. The pore water compression, which was not compensated by
the outflow, causes the formation of AHPP in clay sequences.
These AHPP's often approach the lithostatic values and cre-
ate the environment of slow or practically nonexistent water
exchange.
6. It takes long geologic periods to reach equilibration of the
observed porosity values with their present-day conditions
(depths).
7. Drastic decrease in the porosity decline rate at a depth of
1 km and deeper indicates a practical extinction of gravita-
tional compaction at such depth. The filtration fluid outflow
