Geology Reference
In-Depth Information
in the flank portion of the trough or on most subsided structures (local
invasions through faults of high-alkalinity waters from the lower inter-
vals of the sediment cover).
Ground water flows were produced in the Akhtyr-Bugundyr, Anastasyev-
Troitsk, Fedorov, Malobabchik, Priozernoye, Glazov and other fields. Total
salinity ranges are 5.3 to 200.0 mg-equiv. (1.5-57 g/l), primary alkalinity
factor in the hydrocarbonate-sodium waters, 1.5-65%-equiv., secondary
salinity in the hard formation mixes, 1-8.5%-equiv. and sodium/chlorine
ratio = ratio, 0.93-5.22.
In all waterhead complexes of the Indolo-Kuban trough together with
the described waters are recorded desalinated (to 2 g/l) sulphate- and
hydrocarbonate-sodium varieties typical of the environment of the pres-
ent-day meteoric water infiltration. Except for the uppermost Pliocene,
in all other intervals their distribution covers a relatively narrow band
where the reservoirs are exposed over the adjacent north slopes of mega-
anticlinoriums of the Mountainous Crimea and Caucasus Major, the
band hydrodynamically bounded by the isolating Akhtyr-Parpach fault.
High-salinity chlorine-calcium waters of the regional hydrochemical
background are present in Cenozoic reservoirs in the structures on the
southern flank of the trough directly contacting the fault. This further con-
firms the isolating role of this lineament.
A specific feature of the region's ground waters is a constant presence
beginning at a depth of about 1,500-1,800 m and subsequent increase with
physical and stratigraphic depth in the concentration of the sulphate-ion
(up to 3.5-4 mg-equiv.). Its concentration versus depth is described by the
equation SO
2
−
= 0.12
Н
1.383
. The sulphate concentration in the ground
water as a function of formation temperature (which controls intensity of
the microbial sulphate reduction and the sulphate-ion preservation in the
formation water against this reduction) is described by the equation SO
2
−
= 1.16
⋅
10
-4
⋅
t
1.856
(see Figures 2.22, 2.23).
The source of a drastic enrichment of the high-alkalinity Jurassic waters
in the sulphate-ion is believed to have been the Upper Jurassic Tortonian
salt sequence. Apparently, it also affected the ground waters in the Lower
and Upper Cretaceous complexes. In the latter two cases there is another
acting factor. It is the thermochemical effect of the filtration leaching in the
water-saturated rocks under elevated formation temperature. According
to the model by Kissin and Pakhomov (1967, 1970), Kononov (1965) and
Krasintseva (1968), this results in additional supply of sulphates into the
water medium. The same mechanism also controls growth with depth in
the sulphate content of the hard chlorine-calcium background waters in
the Cenozoic complexes.
⋅
10
-4
⋅
