Geology Reference
In-Depth Information
The described pattern in the spatial distribution of the ground water
salt composition and salinity enable the evaluation of the role and value
of various geologic factors and mechanisms in the formation of the water
medium outlook in the natural reservoirs as well as their hydrochemical
vertical and lateral zoning.
There are special features in the appearance of the low-salinity high-
alkalinity hydrocarbonate-sodium waters in the high-salinity chlorine-cal-
cium water medium of the Paleocene-Pliocene stratigraphic volume. They
form negative hydrochemical anomalies associated with most faulted areas
of the structures and distort rigid regional background; they determine a
foreign nature of their presence in the reservoirs caused by the penetration
of an alkaline agent from the underlying Mesozoic complexes. Under this
model the chlorine-calcium background solutions of the Cenozoic com-
plexes are interpreted as derivatives from direct metamorphism of the ooze
waters of the corresponding depositional basins under arid environment
of the near shore-lagoon shallow-water facies after Valyashko (1964) and
Kapchenko
et al
. (1972).
Ultra-alkaline (the primary alkalinity factor 41-62%-equiv.) low-salin-
ity (6-13 g/l) hydrocarbonate-sodium waters are regionally distributed in
the Lower Mesozoic complexes. Certain factors enable the interpretation
of these waters as the integral result of the interaction between originally
low-salinity ground waters and the enclosing clastic-(Lower Cretaceous)-
carbonate (Upper Jurassic, Upper Cretaceous) rocks. The factors include
thermobaric environment in the natural reservoirs and the composition
of the water-dissolved and spontaneous gas medium. The interaction
occurred during inter- and intra-formational lacunas. The low-salinity
ground waters experienced some influence from depositional synge-
netic waters maximum saturated with thermo-metamorphic and possibly
endogenous carbon dioxide (Kissin, Pakhomov, 1967; Lagunova, 1973;
Pakhomov, Kissin, 1968). This interaction was accompanied by the dilu-
tion of the formed formation solutions by the desalinated alkaline sul-
phate-containing “reborn waters” (Kapchenko, 1978; Kolody, 1985) from
the dehydration of clay minerals.
The simultaneous occurrence of both mechanisms (the major first and
the supplementary second one) results in the accumulation in the generated
waters of carbonate, bicarbonate, sulphate and sodium ions. This process
determines the formation of medium hydrocarbonate-sodium type water.
t
Contrary views present at least three reasons for low-salin-
ity high-alkalinity waters in the Mesozoic complexes hav-
ing paleo-infiltration origin (Yermolayev, Kotov, Rogoshin,
