Hydrogeochemical Field of the Alpine Mobile Belt Basins - Fluid Dynamics of Oil and Gas Reservoirs - page 33

total alkalinity ranges between 0.4 and 4.5 mg-equiv.; sodium and potas-
sium are present in concentrations 10-23.4 mg-equiv. Primary alkalin-
ity А varies between 0 (hard waters) and 31.4%-equiv., secondary salinity
S 2 between 0 (alkaline waters) and 6.3%-equiv., secondary alkalinity a,
between 1.4 and 9%-equiv.
Ground water parameters for individual Mesozoic stratigraphic inter-
vals are included in Table 2.2 (Akhundov, Mekhtiyev and Rachinsky, 1976;
Durmishyan , Muradyan and Rachinsky , 1973).
The following conclusions were made based on the compound anal-
ysis of water chemistry from all Mesozoic intervals vertically as well as
area-wise (Tables 2.1, 2.2) (Akhundov, Mekhtiyev and Rachinsky, 1976;
Durmishyan , Muradyan and Rachinsky , 1973):
t Up the section of individual local highs and of the entire
region against the background of the continuous pri-
mary salinity increase the ground water primary alkalinity
decreases from 12.4-58.4%-equiv. in the Middle Jurassic
and Valanginian to 0.5-0.7%-equiv. in the Cenomanian and
Santonian. Together with these changes at a number of pros-
pects the water type also changes: the alkaline waters in the
lower section are replaced by the hard water ( S 2 up to 6.3%-
equiv.) in the upper section.
t Except for clear cases of a local percolation of the surface
waters, the total salinity experiences a definite increasing
trend.
t On the individual structures in all intervals of the Mesozoic
section, waters of maximum alkalinity and minimum salin-
ity are localized in the crestal and most faulted zones. With
the distance from these zones the ground water salinity
increases, the alkalinity decreases and the salt composition
gradually becomes dominated by the components making
the water hard.
t The areas of hydrocarbon saturation and intense oil shows
are accompanied by the waters least saline and most alkaline
in the particular stratigraphic interval.
t Regionally, a clear ground water salinity increase is recorded
in the Cretaceous in the direction of the regional dip and
weakening of local structures' faulting. It is accompanied
by the appearance and continuous growth in the ion-salt
composition of the calcium and magnesium chlorides
(Figure 2.1).