Geology Reference
In-Depth Information
The following general conclusions have been made based on hydro-
chemical data for the Maracaibo Basin:
t
The sediment fill's vertical hydrochemical zoning in the region
is normal: down the section low-salinity (10.0-16.8 g/l)
background hydrocarbonate-sodium waters in the Cenozoic
series (primary alkalinity factor is 6.3-46.2%-equiv.) are
replaced in the Mesozoic section by higher-salinity (43.7-
61.4 g/l) chlorine-calcium formation waters (secondary
salinity factor 31.3-58.7%-equiv.);
t
In the Paleogene-Neogene stratigraphic range, the ground
water distribution by the component composition and salin-
ity within local oil and gas structures has a mosaic nature.
Their productive blocks are associated with faulted areas of
the structures' hydrodynamic drainage zones. They show the
appearance against the general background of low-salinity
alkaline waters of hydrochemically-anomalous higher-salin-
ity (by the factor of 1.5-3) solutions (often hard and “tran-
sitional”). These solutions define the general outlook of the
salinity decline and alkalinity growth (by a factor of up to 2)
in the ground waters from the crests of folds to their flanks.
The ground water salinity and type change in the stated direc-
tion occurs through the sequential areals of chlorine-cal-
cium, “transitional” chlorine-magnesium, sulphate-sodium
and
hydrocarbonate-sodium waters gradually transiting into
typical alkaline waters of the regional background;
t
Total salinity and secondary salinity factor of hard waters
that show up against the background of the alkaline waters
regularly decline up the section.
Ground water distribution patterns in combination with the general
geologic information provide the opportunity to estimate the role and sig-
nificance of various factors and mechanisms affecting their origin, and con-
ditions of their formation and distribution in the region's sediment cover.
The regional hydrochemical profile of the Maracaibo Depression's sedi-
ment cover is characterized by a drastic ground water salinity decrease
and alkalinity increase up the section. It displays a contrasting manifes-
tation of a genetic association between the formation medium chemistry
and basin's geologic evolution, depositional environments and the result-
ing rock facies. As an example, the normal near-shore marine carbonate-
sandy-clayey Cretaceous facies corresponds with the syngenetic saline (up
