Geology Reference
In-Depth Information
must have been supplied from other sources. Numerous observation in
the region indicate that the subsurface water reserves could not have been
replenished through the surface infiltration (Akhundov and Rachinsky,
1976; Rachinsky, 1984).
Then, there is a possibility that the sedimentogenic waters have been
replenished by the internal resources of complexes (in particular, the
compaction water) (Tables 5.3, 5.4). Table 5.3 shows that clay compaction
within this section may have given rise to the release of up to 54,000 km
3
oil-
water. That would account for only 60% of the water deficit. The reservoir
compaction over the same period may have added 18,000 km
3
of water
(20% more) to this amount (Table 5.4).
Thus, the total amount of replenished water accounts for only 80%
(72,500 km
3
). In the absence of the infiltration feed, the missing 20%
(17,500 km
3
) must have been derived from the underlying sediments.
The Miocene-Paleogene and Mesozoic underlying formations have low
permeability, which suggests existence of vertical intraformational fluid
cross-flows in the region. The latter might have occurred mostly through
faults, fractures, and mud volcanoes (Rachinsky, 1982; Rachinsky, 1984;
Rachinsky, 1989).
The above evaluation negates the elision nature of water-exchange in
this zone of the South-Caspian Basin. This is supported by the occurrence
of AHFP only in the Middle Pliocene structural traps. The AHFP is absent
beyond OWC or GWC in a number of fields (Garadag, Zyrya, Dzhanub,
Gum-Adasy, Bakhar, Ogurdzhaly, W. Ordekly, etc.) (Rachinsky, 1977;
Rachinsky, 1982; Rachinsky, 1989).
Thus, the writers believe that the Pliocene fluid-pressured complex in
the South-Caspian Basin is a complex hydrodynamic reservoir. Its central
subsided portion is filled-up with clays having AHPP and is hydraulically
disconnected from its peripheral areas. The flank areas, composed of alter-
nating sands and clays, are characterized by mostly vertical fluid dynamic
communication with the underlying intervals. This causes the formation of
epigenetic AHFP in the reservoirs over the local highs due to injection of
high-pressured fluids into the section.
Similar estimates have been made for some other regions (e.g., Indolo-
Kuban (Tables 5.5, 5.6), the Tersk-Caspian, and Gulf Coast with simi-
lar conclusions). As in the case of South-Caspian Basin, the maximum
amount of fluids were squeezed out at (1) shallow depths (no deeper than
1,500 m), (2) low temperatures, and (3) the earliest stage of formation of
hydrodynamic system (complex). This occurred long before its function-
ing as an oil- and gas-generating elision system. As the further compaction
