Geology Reference
In-Depth Information
veils their injection nature and creates the impression of their develop-
ment everywhere, therefore the impression of inversion. The reason is a
combination in that area of the geologic conditions facilitating a large scale
of injection manifestations.
2.1.1.3
On the Origin of the Sediment Section's Ground Waters
Our study did not have the objective of special review of the syndeposi-
tional chlorine-calcium brines and injection of alkaline waters in forma-
tion conditions. This issue is currently far from a definitive solution. We
can only talk now about how accurately the actual water distribution in the
section matches this or that hypothesis of its origin.
The actual hydrochemical data for the South Caspian Depression sug-
gest that the high-salinity chlorine-calcium waters common in the region
are a product of deep metamorphism of the source depositional marine
ooze water. This metamorphism proceeded according to a hypothesis of
marine water concentration under the near-shore-lagoon environment
in the arid climate. The hypothesis was developed by Strakhov (1962),
Valyashko (1964), Kapchenko (1974) and other scientists. An additional
factor that could have facilitated the increase in hard brines salinity within
local oil and gas structures may have been formation water in-reservoir
evaporation. It could have occurred in the process of phase transitions
accompanying the liquid hydrocarbon generation from the source steam/
gas gas-condensate mix transiting through the sediment cover (Akhundov,
1957; Kolody, 1969, 1972; Rachinsky, 1981).
The highly alkaline low-salinity waters in the Middle Jurassic-
Valanginian interval are believed to be the integral result of several sequen-
tial and superposed processes. These processes include:
t
Paleo-infiltration of fresh surface waters during the Late
Jurassic regression, depositional hiatus and partial erosion
of the Middle Jurassic sediments;
t
Filtration leaching of water-containing sediments (enriched
with carbonate-containing mineral association due to
the denudation of rock-forming base magmatites in the
Caucasus Major and Minor). The leaching was normal at the
stage of early diagenesis and thermochemical in the envi-
ronment of elevated formation temperatures during the sub-
sequent immersion stage of the region's geologic evolution
(models by Kissin and Pakhomov (1967, 1970), Kononov
(1965) and Krasintseva (1968);
