Geology Reference
In-Depth Information
stated intervals is 2,000-2,200 m. In the stated last three fields the forma-
tion waters of the nonproductive section (Apsheron and Akchagyl Stages,
Surakhany and Sabunchi formations) are almost identical, whereas in the
adjacent fields with the totally oil-saturated sections (Surakhany, Kala)
waters within the same intervals are drastically different in total salinity
and often in the hydrochemical type.
Even more contrasting is the situation in the fields of the Kyurovdagh-
Neftechala (Lower Kura Depression) and Sangachaly-More-Bulla island
(Baku Archipelago) anticlinal zones. There, a regular decline down the
section of the salinity in the chlorine-calcium waters and the appearance
of the hydrocarbonate-sodium waters is recorded only for the productive
areas of the structures (correspondingly, on the southwestern and north-
eastern flanks). At the same time within the nonproductive northeastern
(Kyurovdagh, Karabagly, Neftechala and Khilly fields) and southwestern
(Sangachaly-More, Duvanny-More-Bulla island) flanks, the alkaline waters
are absent, the salinity of hard brines in the same intervals is two to three
times higher, their composition and salinity are almost stable and do not
show any indications of the inversion change down the section (Akhundov,
Mekhtiyev and Rachinsky, 1976).
The quoted data clearly indicate the main cause of the salinity decline
and change in the water type down the section and over the crestal areas
of the local structures in the region. This cause is the injection in the upper
intervals of low-salinity hydrocarbonate-sodium water from the underly-
ing section.
Study of ground water hydrochemical characteristics for individual
Middle Pliocene fields as a function of the geologic space coordinates (in
the section and over the area) reveals:
t
In the South Caspian Depression, the decrease in ground
water salinity in the section of local highs is always accom-
panied by the parallel increase of primary salinity factors
and decrease of secondary salinity factors in the hard water
environment and by the decrease of primary salinity factors
and increase of primary alkalinity in the alkaline environ-
ment. The water type transition zone is the primary salinity
factor's sign reversal boundary (Figure 2.18).
t
The ground water salinity gradient (salinity change
within the complex's thickness) over the local structure
crests
G
con
w
=
Σ
a
+
K
/
h
PS
(
RS
),
(where
Σ
a
+
K
=
[(
Σ
a
+
K
)
max
−
Σ
a
+
K
)
min
],
h
PS
(
RS
)
is PT-KT thickness) for the basin as
a whole is 7.90 to 89.50 g/l/км; their metamorphism
(
