Geology Reference
In-Depth Information
The following is important in determination of the mechanism of the
mentioned phenomenon. The ground water primary alkalinity is the indi-
cator of the foreign alkaline ingredient's participation fraction in forma-
tion water mixes (Rachinsky, 1970).
In the Productive Sequence, with all
other conditions equal, regardless the trap type it is mostly defined by the
medium's conducting properties. At the same time, per-unit volume oil-
saturation in the accumulations to a substantial extent is also controlled by
the nature of local structural forms. [Correlation
А
=
f
(
k
пр
/
(Figure 8.2),
as opposed to
β
i
3
=
f
(
А
) (Figure 8.1) is not differentiated by the morpho-
logical types of structures and is common for both groups of highs.]
Actual data on geology and oil and gas occurrences of the fields in
the subject region together with the established functional interrelations
between ground water outlook, nature of the hydrocarbon saturation and
reservoir conductivity enable the following conclusion. On all structures
of the Apsheron oil and gas area, the hydrocarbon amount entering an
accumulation in the Lower group of the Productive Sequence as a result of
the transport by the invaded alkaline waters originally could be only of one
order of magnitude. In other words, in the formation of accumulations a
unit volume of the alkaline waters accompanied a more or less determined
portion of hydrocarbons. Any drastic deflection from this ratio toward an
increase in
β
i
3
may be interpreted as evidence of the influx into an already
formed accumulation of additional liquid oil from its aggregations in the
overlying deposits
5
. Under the first scheme were formed the accumula-
tions on predominantly uneroded syndepositional structures. The second
mechanism is typical of the accumulations on deeply eroded structures
with invasion into the Productive Sequence dislocation of Paleogene-
Miocene masses. This conclusion is based on the following:
t
The impossibility of the selective escape of only alkaline
component from the preserved liquid oil accumulations out
of the water in contact with oil.
5
A diametrically opposite interpretation is also a possibility. Initially all accumulations in the subject
region were grouped within the
β
i
3
= f
(А) correlation zone that currently covers the first group of
highs. Subsequently some oil in some of these accumulations flowed over into the upper intervals.
This caused the described differentiation in per-unit saturation by the morphological type of struc-
tures. From the first sight this is a reasonable explanation, especially considering that in the structures
of the second group - the upper group is productive beside the lower group (whereas it is in most
cases eroded in the first group). However, a clear correlation of oil density vs. depth exactly in the
second group of structures is against this mechanism: this couldn't have happened with cross-flows
of the liquid phase.
