Geology Reference
In-Depth Information
drilled there on three structures of the Turkmenistan shelf (Ogurchin,
West Erdekli and Fersman prospects) turned out unproductive. The same
happened with Khazar-1 well (TD 5,570 m) drilled during the same period
in the Iranian sector (Enzeli-Offshore prospect).
Thus, by the end of the 1980's, the understanding could have arisen that
a number of factors are a combination
necessary
but not at all
sufficient
for the formation of commercial oil and gas occurrences. These factors
include:
t
Regional oil- and gas-saturation of some Productive
Sequence (Red-Bed Sequence) Formation or horizon off-
shore the basin.
t
Presence of contrasting structural traps.
t
Good and fair reservoirs (formation water rates in a number
of wells when testing V11 horizon in the Baku Archipelago
reached 570-1,500 m
3
/day (Aran-Deniz, Sabail prospects).
t
Clay barriers of sufficient thickness.
It should have become obvious that the main factors there were not gen-
eral geologic qualitative parameters (trap, seal, reservoir, “source” rocks).
They only describe the
hypothetical probability
of hydrocarbons. The
main factors there are а stringent
quantitative interrelations of tectono-
structural, geothermobaric, hydrodynamical, permeability-porosity and
hydrochemical parameters of natural reservoirs individual for each oil and
gas area and determining the
real probability
of their fill-up with oil and/
or gas (Rachinsky, 1972; 1990; 1996; 2008).
Considering the results of the conducted studies, the attitude to high
estimates of the Productive Sequence (Red-Bed Sequence)
potential
in the
South Caspian Basin
even in the early 1990's
should have been critical and
cautious. It was necessary even at that time to pay careful attention (albeit
on the empirical level) to the following geologic facts, which had become
obvious:
t
Main amounts of liquid hydrocarbons in the region are
associated with the depth interval shallower than 5 km;
the deeper intervals are dominated by gas and condensate
aggregations.
t
Down the regional dip oil and oil-gas accumulations are
replaced by gas-oil and gas-condensate accumulations; in
the same direction occurs the general increase in gas-satu-
ration of the section with stratigraphic and physical depth.
