Geology Reference
In-Depth Information
(see Chilingar
et al
., 2002). This process occurs at a temperature above
120
o
C (Kartsev and Vagin, 1973; Kolodiy, 1985; Khitarov and Pugin, 1966;
Perry and Hower, 1972; Powers, 1976; Chilingar
et al
., 2002), which is typi-
cal for the depths between 7 and 9 km in the South-Caspian Basin.
In conclusion, the generation of the amount of water by clay sequences
within the depth range of 0.6 to 8 km necessary for functioning of the eli-
sion hydrodynamic system is unlikely.
Conclusions
Based on studies, clay porosity vs. depth correlation should not be
approximated by logarithmic or exponential functions, which is a com-
mon practice rooted in formal statistical averaging of clay porosities.
Instead, it would be more accurate to approximate it by a linear func-
tion with a jump-like function break within the minus 500 to minus
800 m range (depending on the local geological scenario). The inter-
val of drastic porosity decline shallower than this range represents the
zone dominated by the filtration discharge (squeezing-out of water).
The interval of slow porosity decline deeper than 1,000 m represents the
zone dominated by the processes of diffusion, capillary, film and osmosis
(Rachinsky, 1983).
The writers identify the following hydrodynamic stages in the geologic
evolution of thick clay sequences:
1. Filtration (squeezing-out of water) compaction in the depth
range of up to
2. ≈ 500-800 m.
3. Diffusion-film compaction deeper than 800 m.
4. Catagenetic dehydration within the temperature zone above
120
o
C.
The two latter processes may overlap.
The writers also conclude that the Darcy model in hydrogeological cal-
culations should be used only for the upper filtration zone.
The discharge of compressed fluids (AHFP with large reserves of elastic
energy) from thick, deep, hydrocarbon-producing clay sequences may be
possible over a significant area creating conditions for the regional oil and
gas occurrences. The extent of such fluid discharge may be relatively small
and may produce noticeable results only over long time intervals (hun-
dreds of millions of years).
