Geology Reference
In-Depth Information
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Local appearances of low-salinity high-alkalinity waters
against the background of high-salinity chlorine-calcium
water medium form negative hydrochemical anomalies in
the Cenozoic waterhead complexes. They are associated
with the strongest faulted areas of individual structures.
Negative hydrochemical anomalies in the Upper Eocene and
Oligocene-Lower Miocene complexes within the trough's
axial portion show up as local zones of more alkaline and
less saline varieties against the background of the hydrocar-
bonate-sodium water medium.
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In the Cenozoic complexes on local structures the ground
water salinity from maximum faulted crests to less faulted
peripheral portions gradually increases. Simultaneously,
a regular replacement of their genetic type occurs from
the hydrocarbonate-sodium in the areas of hydrochemi-
cal anomalies through “transitional» sulphate-sodium and
chlorine-magnesium to the background chlorine-calcium
type.
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Up the Cenozoic section the low-salinity alkaline water are-
als within local structures gradually decrease. Total salin-
ity of the hydrocarbonate-sodium waters' hydrochemical
anomalies increases in the same direction and the primary
alkalinity factor, decreases.
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In all Cenozoic complexes the highest salinity and metamor-
phism chlorine-calcium waters are found close to the reser-
voir exposure areas on the trough's southern flank.
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Commercial hydrocarbon saturation in the Cenozoic com-
plexes of the trough's fields is usually associated with are-
ally-limited developments of medium-saline (12-17 g/l)
alkaline waters (forming negative hydrochemical anoma-
lies) or with the areas of chlorine-calcium waters of the
salinity and hardness substantially lower than the back-
ground ones.
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In all intervals saturated with chlorine-calcium waters salin-
ity and secondary salinity factor values increase in the pro-
cess of field development. In the reservoirs with alkaline
water medium the primary alkalinity factor values decrease
with the increase in salinity. In the Upper Eocene and
Oligocene-Lower Miocene complexes of the trough's axial
zone fields the formation solutions salinity decreases and the
primary alkalinity factor increases.
