Geology Reference
In-Depth Information
alkalinity (or even the appearance of hard varieties against the alkaline
background) in the oil-saturated areas compared with beyond-the-OWC
areas (see Table 2.11). A satisfactory explanation involves the mixing of the
lower chlorine-calcium brines of the Mesozoic origin and syndepositional
alkaline background waters. Modeling these processes using mix design
techniques shows reasonable comparability of the results with actual for-
mation water composition and salinity for different Neogene intervals.
When successively mixing hard brines (
Σ
а
+
k
455 mg.-equiv.) with hydro-
carbonate-sodium waters from the Burdigalian-Helvetian, Tortonian,
Sarmatian and Pannonian Stages (
Σ
а
+
k
52.6; 40.9; 30.4 and 13.2 mg.-equiv.),
formation mixes with decreasing up the section content of the foreign
chlorine-calcium component (115; 12; 11; 3%) correspond to the waters of
the productive areas from the said intervals with salinity correspondingly
105.7; 95.8; 75.7 and 23.2 mg.-equiv.
The sulphate-ion distribution data in the vertical section suggest a simi-
lar conclusion. There is only low probability of its preservation as a relic of
the salt composition in the Neogene depositional basin waters due to the
deposits transit through the zone of actively functioning sulphate-reducing
microflora (Kuznetsov, Ivanov and Lyalikov, 1962; Rachinsky and Aliyev,
1973). Due to this and due to the enriched in SO
2
−
evaporite accumula-
tions in the Mesozoic sequence, the invasion of the Neogene interval by the
foreign sulphate-containing waters of Mesozoic generation are believed to
be the major factor of the sulphates appearance and accumulation in the
water medium.
The study of hydrochemistry in the Viennese Basin gives a reason to
consider the injection of its section (replete with syndepositional hydro-
carbonate-sodium waters) by chlorine-calcium brines from leaching of
the Mesozoic evaporites as the main formation mechanism of the ground
water ion-salt composition, salinity and spatial zoning in the productive
intervals of the upper stage.
2.1.4
The Irrawaddy-Andaman Depression
In the sediment cover of the depression are identified Eocene, Oligocene,
Miocene and Pliocene waterhead complexes separated by regional barri-
ers (clays of formations Laungsche in the Lower Eocene, Yau in the Upper
Eocene and the upper part of Pyaubve in the Lower Miocene).
Hydrochemical information about the region is limited, incomplete
and extremely desultory. It was published that the prevailing ground water
type in the clastic Cenozoic series is hydrocarbonate-sodium. Total salin-
ity does not exceed 12
−
25 g/l, primary alkalinity factor is 20
−
45%-equiv.
