Geology Reference
In-Depth Information
of the South Caspian Sea. It may be upgraded to a modest optimism if a
totally different view regarding the trap and accumulation formation tim-
ing is accepted in the forecast of the hydrocarbon saturation.
According to this view, deeply subsided natural reservoirs in the cen-
tral South Caspian Basin may not necessarily be evaluated pessimistically
and may have a chance to be hydrocarbon-filled. The necessary condi-
tion is that the accumulation occurred prior to the region's active subsid-
ence when avalanche deposition of the upper Apsheronian-Quaternary
sequence occurred. The sequence reaches the thickness of 2.55 km at
Nauchnaya structure, 2.978 km at Seyar, 3.5 km at Mushwig (D-31), 3.8 km
at Turkmenabat, 5.6 km at Abida (D-29), 6.0 km at Natavan (D-22), 6.4 km
at Sanani (D-28) etc. This means that the top of the Productive Sequence
(Red-Bed Sequence) was at depths of up to 1,700-1,800 m, providing for
the efficient drainage fluid-mass exchange (see above).
The necessary item under this type of a geologic environment is the
completion of the zone's (block's, step's) tectonic plan and the final struc-
tural and fault arrangement on the local highs. Timewise, all these are
synchronous with the main hydrocarbon migration phase within the
entire South Caspian Basin, which occurred at the time of the Pliocene
(Akchagyl-Lower Apsheronian) stratigraphic interval. Helpful at that may
be satisfactory reservoir properties of the potentially productive intervals
at depths of up to 8.5-9 km (Buryakovsky, Chilingar
et al
., 2001)
1
and reli-
able sealing properties of a thick overlying sedimentary series conserving
hydrocarbon accumulations.
A hypothetically possible option within the suggested model is the
following geologic situation. Let us assume the trap's structure had not
completely formed yet as a natural reservoir prior to the beginning of the
main and final hydrocarbon migration phase. Thus, the migrating fluids
bypassed it without delay up the regional dip. Naturally, in such a case, the
trap will be empty even if all other necessary and sufficient factors of the
hydrocarbon accumulations are present.
A case is also obvious where the trap was eroded to a substantial depth
so the accumulations it housed were totally degraded (fields Girmaku,
Tafmai, Khamamdag-Deniz, Garasu, Sangi-Mugan, Ulfat and others).
At the present state of knowledge, a more or less reliable quantitative
reserves, resources and geologic potential estimation of the deep-water
1
The reservoir presence in this area may be in doubt due to a strong shale-out of
the Productive Sequence (Red-Bed Sequence) in the direction from the basin's
periphery toward its center. MZR
.
