Geology Reference
In-Depth Information
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Drastic permeability deterioration in the carbonate part of
the section (Cretaceous-Paleocene) from the flanks to the
center of the depression.
On local productive structures in the flank zones, where oil- and gas-
saturated reservoirs are exposed, the meteoric water invasion is limited
and does not affect general hydraulic environment and hydrochemical sit-
uation in natural reservoirs outside of the lower oil-water contact (OWC).
The fresh water zone in all fields of this type (Lagunilias, Biscan, Encenada,
Mene Grande and others) involves only head portions of the reservoirs and
does not extend for more than 5-10 km. It is reliably blocked by the upper
OWCs where hydrocarbons on contact with it form asphalt and kir “plugs”
sealing the reservoir (Dickey, Hunt, 1975; Kartsev, Vagin and Matusevich,
1986). Typically, in a lower outside-of-OWC zone of these oil-saturated
intervals, the water is depositional with features of genetic association with
ooze-silt water of the depositional basins (Chapter 2).
General geologic factors determining low likelihood of an infiltration
waterhead system functioning in the region are also significant for the
water-exchange under the elision model. We described the tectonic and
lithofacies blockage of lateral water flow, which would refract (change)
lateral direction of the migration into the direction perpendicular to the
lamination and seriously limit the possibility of forming the squeeze-out
(elision) regime in water complexes. Other such factors are:
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The lack within the depression's sediment cover of thick
uncompacted clay sequences capable of serving as source
for elision charge.
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High compaction of relatively thin clayey beds and members
due to significant sand content of the section (up to 45%). It
determines low likelihood of squeezing from them sufficient
pore water amounts needed for the emergence, existence
and sustenance of the flow in time and space.
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Shale-out of the clastic part of the section (Eocene-Pliocene)
in the central depression. It prevents the updip fluid flow.
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Rather low compactability of carbonate reservoirs
(Cretaceous-Paleocene) and their practical impermeability
in the horizontal direction.
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“Wedge-like” replacement in the clastic part of the section of
permeable and impermeable varieties. It facilitates the for-
mation of dead-end hydrodynamical zones.
