Geology Reference
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interformational hydraulic communications. Clearly, the invasion of alka-
line waters could occur only after they formed, and subsequently in the
periods of active tectonic manifestations, i.e., when the conductivity of
preexisting unconformities increased and new disruptions of rock integ-
rity formed.
Based on paleo-tectonic reconstructions covering time interval of end
Late Pliocene through Quaternary, researchers (Durmishyan, Muradian
and Rachinsky, 1974) identified the following major phases of the hydro-
carbonate-sodium water migration into the Pliocene section (the phases
match the corresponding cycles of regional neotectogenesis):
1. Upper Pliocene (Akchagyl-Apsheronian). At that time,
against the background of the South Caspian Depression
subsidence, elements of fault tectonics develop on most local
highs. The injection scale was limited.
2. Quaternary. Accelerated structural growth was recorded at
that time, accompanied by partial erosion, mud volcanism
and fault formation. The volume of invaded alkaline water
was maximal and determined the present-day spatial hydro-
chemical zoning.
3. Recent. It is the manifestation of neotectonic processes
and earthquakes; mostly intraformational fluid cross-flows
occur.
The domination of the Quaternary phase determined a single-stage
Pliocene section saturation nature with alkaline water and hydrocarbons
(see Chapter 6). This is supported by:
t Regular salinity decrease and alkalinity increase with depth
observed in the fields.
t Consistent growth in the same direction of oil and conden-
sate density (Mekhtiyev and Rachinsky, 1967; Mekhtiyev,
Tsaturiants and Rachinsky, 1968), which could occur only if
the fluid invasion process was continuous.
Predominantly vertical saturation of the Middle Pliocene reservoir
with migrating fluids is also supported by petroleum geology evidence. In
particular, in most Middle Pliocene fields the oil-saturated area of indi-
vidual accumulations declines from the bottom upward. This causes the
cone-shaped hydrocarbon reserves distribution (Bibieybat, Surakhany,
Kala, Zyrya, Sangachaly-More - Duvanny-More - Bulla Isl. and other
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