Geology Reference
In-Depth Information
2,0
1,8
1,6
1,4
1,2
1,0
0,8
0,6
100 200 300 400 500 600 700
S
,m
Figure 8.3
South Caspian Depression. Per-unit volume oil saturation vs. distance from
base of Middle Pliocene Productive Sequence. See Figure 7.2 for legend.
accumulations and their upward distance to the base of the Productive
Sequence in the Central Apsheron fields. As Figure 8.3 shows, the accumu-
lations positioned in the direct vicinity of the Productive Sequence base,
i.e., in the area of elevated waterhead of the invading fluids, regardless of
the porosity of reservoirs, have relatively depressed absolute values of the
per-unit volume oil-saturation. With the distance from the Productive
Sequence base up the section and still reaching maximum value of this
parameter (200-250 m), the oil-saturation of accumulations increases.
After that, it monotonously declines, thereby reflecting a total pattern of
declining waterhead with the distance from the source. Naturally, just in
this basal interval of the Productive Sequence (the contact zone with the
underlying deposits) are almost everywhere reported intense abnormally
high formation pressures as they are genetically associated with com-
paction of thick Paleogene-Miocene and Mesozoic clay formations. The
available data give reason to believe that just this factor causes elevated
waterhead gradients of the migrating fluids and prevents their preservation
in the traps of the Productive Sequence's lower intervals.
It is important (Figure 8.2) that each of the identified zones of correla-
tion
А
=
f
(
k
пр
/
) corresponds with a certain accumulation group
4
.
4
This correlation is based mostly on the accumulations from the Lower Productive
Sequence. Information on the Upper group (“Pereryv” Fm. accumulations) was
used only for the West Apsheron. For that area, this interval is one of the basal
ones and from the hydrocarbon accumulation viewpoint, it plays there the same
role as PK, KS and NKP formations in the East and Central Apsheron.
