Geology Reference
In-Depth Information
invasion of low-salinity alkaline waters from the overlying complexes into
the productive Middle Pliocene section originally saturated with synge-
netic chlorine-calcium brines.
In a peculiar hydrogeological environment of the Productive
Sequence saturated with waters of various origins and their mixes, the
establishment of predominant association between hydrocarbons and
certain genetic ground water type may be viewed as a reliable evidence
of a primary or secondary nature of their aggregations. Wherever the
main hydrocarbon reserves in the region as a whole and in the sections
of individual fields contact high salinity chlorine-calcium waters, this
correlation could be interpreted as a confirmation of their syngenetic
nature in the enclosing intervals. The predominant association between
the hydrocarbon saturation and alkaline waters genetically foreign to the
Productive Sequence may be classified as evidence of its allochthonous
nature. On the other hand, the presence or absence of these associations
provides an opportunity to evaluate the role and participation extent of
foreign hydrocarbonate-sodium waters in the formation and dissipation
of accumulations.
When discussing the aforementioned issues, it should be kept in mind
that individual fields and oil-gas-saturated intervals in the section of local
structures (formations and horizons) have different lithofacies and struc-
tural conditions. This affects qualitative and quantitative aspects of the
hydrocarbon saturation and the chemistry of the accompanying ground
water. In particular cases the current status of fields and productive
intervals, including the hydrochemical situation in them and taking into
account the aforementioned distinctions and particulars, is represented by
the integral function of effect of the aforementioned factors. Overall, it is
determined by depositional basin's evolution and by the formation pro-
cesses of oil and gas accumulations.
We set a task to establish quantitative association between oil-gas
occurrences and ground water chemistry in individual accumulations.
For this purpose, we studied 82 intervals in the Upper and Lower groups
of the Productive Sequence in 28 most typical fields of the Apsheron
and Lower Kura oil and gas areas (Durmishyan and Rachinsky, 1972).
Parameters for our analysis were selected oil reserves (Russian А+В+С
1
category which approximately corresponds with proved plus probable
reserves); per unit volume of the accumulation (
β
acc
, MT/hectare*m) and
of the trap (β
j
trap
, MT/hectare*m); fill-up factors (volume ratio of the accu-
mulation and trap) and waters' primary alkalinity factors (
А
, %-equiv).
