Geology Reference
In-Depth Information
the sulphate preservation in the syndepositional background waters is low.
The sulphates are a result of lengthy microbial sulphate reduction from the
diagenetic stage to catagenesis. The sulphate content is drastically elevated
in the Mesozoic waters. Thus, we believe that the main source of SO
2
−
ion
introduction into the Cenozoic water is the water injected from below.
The proposed hydrogeological model is directly supported also by dras-
tic hydrochemical anomalies' water enrichment in boron, lithium, mer-
cury and СО
2
to the concentrations typical of the waters in the Mesozoic
complexes (Lagunova, 1973; Lagunova and Kapchenko, 1981).
2.2.3
The Tersk-Caspian Foredeep
The ground waters in the region's sediment cover are mostly hard chlo-
rine-calcium varieties; the chlorine-magnesium, sulphate-sodium and
hydrocarbonate-sodium waters have limited distribution and are mostly
typical of exposed mostly Neogene reservoirs within the influence zone of
present-day meteoric fresh water infiltration (Tables 2.18, 2.19).
Based on the combination of lithofacies, hydrodynamic and hydrochem-
ical factors, it was possible to identify in the drilled sediment complex a
number of waterhead complexes. They include: the Upper Jurassic evapo-
rite facies (the Titonian Stage), the Upper Jurassic carbonate series (the
Oxfordian Stage), the Valanginian, clastic Hauterivian-Aptian series, the
Upper Cretaceous carbonates, the Eocene carbonate-clastics, the Oligocene-
Lower Miocene clastics (the Maikopian formation) and the Middle-Upper
Miocene. The main regional water barriers are the Upper Jurassic salt
sequence (penetrated thickness of up to 500 m), clays of the Albian Stage
(120-210 m) and of the Maikopian Series (200-2,500 m and greater).
Ground waters from reservoir lenses of the
Upper Jurassic
evaporite
facies
were obtained in the Datykh, Elistanzhi, Zamankul, Karabulak-Achaluki,
Malgobek-Voznesenskoye fields. In their hydrochemical type they are
typical chlorine-calcium brines. Total salinity is 1,085.5-1,200.7 mg-equiv.
(321.2-355.5 g/l), secondary salinity factor is 20.6-39.2%-equiv., sodium/
chlorine ratio = = 0.61-0.79. Averages of the listed values are typical of the
regional background. These values do not show significant variations over
the trough area.
Ground water flows from the
Upper Jurassic - Valanginian
dolomitic
limestones and dolomites were produced at the prospects on the Chernogor
monocline (Datykh, Syuret, Benoy, Elistanzhi, Argun, Pervomay); in the
Sunzha zone (the Kharbizhin, Zamankul and Karabulak-Achaluki fields);
in the Tersk zone (the Arak-Dalaterek, Malgobek-Voznesenskoye, Ali-
Yurt, Khayan-Kort and Eldarovo fields); and in the Pri-Terek zone (at
