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oil-saturated flank these attributes are respectively 2.2 mg-equiv. and
15.1%-equiv. (well 30).
Typically there is a trend of increasing sulphate content in waters on
contact with gas-condensate aggregations as compared with contact waters
of oil accumulations and with waters of unproductive intervals at about
the same depth. For instance, in the gas-condensate accumulation of VII
horizon (Karadag field), SO 2 ion content in the formation waters of the
aquifer is on average 4.1 mg-equiv. In the same horizon of the Duvanny-
More Field containing an oil accumulation at about the same depths as in
the former case, the sulphate content is about two times lower and is 2.2
mg-equiv., etc.
Let us look at individual anticlinal zones that are reasonably similar
within their limits of oil-gas-saturation (about equal for each field hydro-
carbon reserves per unit volume of the pore space caused by more or less
equal presence and participation in the mix of alkaline invaded waters).
The interrelation between the sulphate content in formation waters and oil
and gas occurrences, which in the regional plan is strictly qualitative, pro-
vides an opportunity for a quantitative approach. It follows, for instance,
from the aforementioned data on the Baku Archipelago fields. In this case
the SO 2 ion content in the formation waters in concentrations lower than
1.0 mg-equiv. with the primary alkalinity factor of up to 8-10%-equiv.
gives reason with certainty to evaluate such intervals as nonproductive.
Based on the aforementioned, the connection between the sulphate con-
tent of waters, their alkalinity and oil-gas-saturation allows judging about
the reasons of hydrocarbon absence in traps. In a case when the formation
waters do not have sulphates in their composition or their content at a
given depth is much lower than it should have been from Figure 2.12, then
on condition of low alkalinity ( А ) or hard nature of the waters, this circum-
stance says that this trap never in the geologic past has been saturated with
hydrocarbons.
A different situation occurs in the water medium of hydrocarbon aggre-
gations destroyed by hydraulic action. Formation waters in such traps are
usually enriched in sulphates and their alkalinity is somewhat higher (sec-
ondary salinity substantially lower in the hard water medium) than in the
adjacent fields, which preserved their accumulations. An explanation is
that in the formation of accumulations, the amount of hydrocarbons com-
ing into a trap is incompatible with the amount of ground waters trans-
porting them. The disruption of dynamic equilibrium in favor of water
unavoidably results in oil washout from the trap.
Examples of such destroyed accumulations are the VII th horizon on
the north flank of Dashgil Field, PK Formation over the SE plunge and
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