Geology Reference
In-Depth Information
The first zone is dominated by the accumulations associated with strati-
graphic interval of the lower group's section most remote from the base of
the Productive Sequence (NKP Formation). It is also dominated by accu-
mulations of the intervals with lowered conductivity of their enclosing res-
ervoirs (formations KS and KaS) or with insufficient fault conductivity or
both. A common feature for the accumulations in this zone is the presence
in the overlying Productive Sequence intervals of basal reservoirs, which
accumulated substantial absolute hydrocarbon reserves.
The second zone of the
А
=
f
(
k
пр
/ ) correlation includes accumulations
positioned in all stratigraphic units of the Productive Sequence's Lower
group and in the “Pereryv” Fm. Parameter values determining in each
individual case their position relative to the resulting curve are caused by
the combined action of all aforementioned local causes. In the correlation
segment corresponding with maximum for the zone values of the primary
alkalinity are usually grouped the accumulations positioned in the basal
intervals of the Productive Sequence (KaS and PK formations) or in the
overlying stratigraphic units (NKP and “Pereryv” Formations of the West
Apsheron).
The precondition for the accumulations' location exactly in this zone is,
contrary to the previous case, the absence in their underlying portion of
the Productive Sequence section of thick oil-saturated intervals. In other
words, traps in this zone are saturated with the migrating fluids on a first
priority basis. Within the subject zone minimum values of the per-unit
volume oil-saturation in the accumulations, hence, of ground water alka-
linity are typical of the Kirmaki Formation least conductive and remote
from the Productive Sequence base.
The third zone includes accumulations in most diverse stratigraphic
positions that have two grouping attributes. The first is continuous associa-
tion of hydrocarbon aggregations with the reservoir members closest to
the base of the Productive Sequence, and the second is a high conductiv-
ity facilitating ground water dynamics. A negative role of the latter factor,
besides the accumulations presented in Figure 8.3, is especially demonstra-
tive in the “Pereryv” Fm. and lower Balakhany Fm., which are water-satu-
rated everywhere in the Central Apsheron and are composed of reservoirs
with permeability exceeding 1,000 mD.
As mentioned earlier, with equal ground water primary alkalinity, the
per-unit volume oil-saturation in the accumulations within the denuded
diapir structure group is substantially higher than in the accumulations of
slightly eroded syndepositional structures (Figure 8.1). We believe that the
causes of it are in the specific formation environment of the accumulations
in each of the stated morphological groups.
