Geology Reference
In-Depth Information
t
Leaching of salt-enriched clayey rocks in the process of
water flow;
t
Paleo- and present-day infiltration of meteoric waters into
the intervals currently saturated with the alkaline waters;
t
Progressive salinization of the Pliocene depositional basin;
t
Middle Pliocene's penetration by fresh infiltration waters
from Cretaceous sediments.
t
Condensation-distillation phenomena.
t
Sulphate reduction processes accompanied by the gen-
eration of carbonates transforming a hydrochemical out-
look of the ground waters.
Critical review of these hypotheses and views (Rachinsky, 1983) revealed
their incapability to explain many factors. Among these factors are:
The origin of «transitional» waters; correlation of the water ion-salt
composition and salinity vs. distance between the water-saturated objects
and the base of the Middle Pliocene;
Waters' spatial distribution patterns vs. well position on the structure
and vs. litho-reservoir and structural specifics of particular prospects and
areas; Causes of a continuous association between the hydrocarbonate—
sodium waters and fault zones;
A genetic association between the hydrocarbon saturation and alkaline
waters; etc.
Taking into account hydrochemical similarity of all (Hauterivian and
up) water intervals of the section, we will review (using as an example best
studied Pliocene sediments) the formation schematics of hydrochemical
zoning in the Meso-Cenozoic, which corresponds with the above bullets.
The “transitional” waters and their origin as indicators of the
ground water
ion-salt composition and salinity formation
processes
(Mekhtiyev, Rachinsky and Akhundov, 1966; Mekhtiyev and Rachinsky,
1967; Mekhtiyev, Akhundov and Rachinsky, 1970).
Replacement down
the section of the fields of the chlorine-calcium water type by the hydro-
carbonate-sodium one occurs, as noted above, through transition zones.
These zones have specific composition and salinity and usually include
several intervals of the section. (What we mean is a sporadic appearance
of the “transitional” waters in stratigraphic units saturated with waters of a
different chemical outlook.) These zones may include waters of any known
hydrochemical type. Their composition is always dominated by the pri-
mary salinity ion-salt complex (92-98%-equiv.); the secondary salinity or
primary alkalinity are subordinated (0-8%-equiv.); the secondary alkalin-
ity reaches 6-8%-equiv. A distinctive feature of the “transitional” waters in
