Geology Reference
In-Depth Information
Regional and local faults play a dual role. First, they serve as commu-
nication channels between different stratigraphic intervals of the section
and determine vertical hydrochemical and hydrodynamic zoning. Second,
they are barriers preventing (in part or completely) lateral ground water
flow and causing its areal zoning (Durmishyan, Rachinsky and Malysheva,
1971; Mekhtiyev and Rachinsky, 1967).
The following was established based on hydrochemistry of individual
fields and anticlinal zones in the South Caspian Depression (see Chapter 2).
It is possible to identify the conductive or barrier function of faults in the
Pliocene of the region (saturated with syngenetic chlorine-calcium brines
and invaded from down up with low-salinity ultra-alkaline waters and
their mixes) by uncovering the predominant association of hydrocarbon-
ate-sodium water with certain intervals of the section and areas of specific
prospects. A discovery of them individually or as increased fraction in the
formation mix may be interpreted to be a result of intercommunication
between the stratigraphic complexes. Their fraction is identified from a
decreased salinity and secondary salinity factor in the hard water medium
(increase in primary alkalinity factor in the alkaline water medium). The
isolating role of faults is established based on drastic changes in the water-
head, salinity, secondary salinity factors, primary alkalinity and genetic
types of water in different tectonic areas, blocks, flanks and structural
plunges. Examples of this dual role are available in the Central (Bibieybat
and Balakhany-Sabunchi-Ramany), Eastern (Buzovny-Mashtagi) and
Northwestern (Binagady, Sulutepe and Chakhnaglyar) Apsheron and
at a number of prospects in the Apsheron Archipelago and Lower Kura
Depression (Durmishyan, Rachinsky and Malysheva, 1971; Mekhtiyev and
Rachinsky, 1967).
In a contrasting way, simultaneous conductivity and blocking are
encountered in the Lower Kura Depression fields. The general background
in all anticlinal lines and all prospects there is relatively saline chlorine-
calcium water. Everywhere in the fault and mud volcano zones, alkaline
water without any genetic association with the enclosing water medium
is encountered. The conducting nature of faults is especially obvious at
Kyurovdag (where the most faulted crestal area of the southwest flank is
filled with water from the underlying horizons, which moved the oil accu-
mulation of the Productive Sequence Horizon I downslope [(Gurbanov,
Moldavsky and Rachinsky, 1966), Kalmas (Mekhtiyev, Akhundov and
Rachinsky. 1970), Neftechala and Khilly.]
Exceptionally contrasting in the subject area is also the blocking role
of faults. It is manifested by a drastic difference in oil-saturation, water
composition, salinity and waterhead on the flanks separated by major
