Geology Reference
In-Depth Information
fields whose ground waters mostly belong to the hydrocarbonate-sodium
type and are of a lower salinity.
At the final stage of the latest hydrogeological cycle (the Wallachian
phase of the Alpine orogeny) hydrocarbons together with the high meta-
morphism depositional chlorine-calcium brines (which migrated from
deeper zones) displaced substantial portion of the paleo-infiltration waters
into the overlying stratigraphic intervals. The brines migrated together
with hydrocarbons. At the differentiation of the oil from the water within
traps they partially mixed with the paleo-infiltration waters (in the Menilite
deposits) or even totally replaced them (in the Eocene formations). Only
part of the primary waters (syngenetic with the reservoirs) was preserved
as irreducible water within the oil-saturated reservoirs of the formed oil
fields.
We relayed here the concept of paleo-infiltration origin of the desali-
nated hydrocarbonate-sodium waters. It is important, however, to dis-
cuss the view (Kolody, 1983) of their thermal dehydration genesis at
great depths and high temperature in the course of montmorillonite clay
minerals and organic matter catagenic transformations. Kolody (1983)
noted that the hydrochemical inversions associated with the low-salin-
ity alkaline waters are quite intense in the areas with the most complete
Paleogene section (the Tanyav Depression). On the contrary, in many
cases the erosions do not affect in any way the ground water salinity
and composition. The ground water desalination is most intense in the
deeply-buried Menilite rocks of the Tanyava Depression where the solu-
tion gas includes, together with methane, also carbon dioxide (up to
25%). For this reason Kolody tends to relate the hydrocarbonate-sodium
type of these waters and their lowered salinity with the processes occur-
ring under a high-temperature environment in the organic-rich Menilite
deposits (Kolody, 1983).
These writers believe that although the described mechanism is realistic,
it is only an additional factor in the water medium alkalinity increase and
salinity decrease. More intense course of this process is limited by the low
thickness of clay beds within the Paleogene flysh.
As the result of the reviewed complex processes, the following three
hydrochemical section types can be identified within the Internal zone of
the Carpathian Foredeep:
1. The Bitkov type. There, the discharge of the depth-originated
chlorine-calcium brines was most complete and the alkaline
paleo-infiltration waters were almost totally displaced by the
migrating agents;
