Geology Reference
In-Depth Information
Syndepositional chlorine-calcium formation solutions of the pre-
Pliocene complexes appear to be products of a long natural metamor-
phism of the marine ground waters according to the models by Valyashko
(1964), and Kapchenko (1974, 1979). Their relatively low salinity (up to
40 g/l) was obviously caused by paleo-infiltration of surface fresh waters
during periods of depositional hiatuses and partial erosion. These hap-
pened between Early Pliocene and Late Miocene, between Middle
Miocene and Oligocene, etc. (Bakirov, 1959; Barbat, 1961). At those times
meteoric waters partially flushed reservoir members of the pre-Pliocene
stratigraphic range. The mechanism of additional influence on the salin-
ity decrease was a hydrochemical effect of generating the clay minerals in
the “reborn” waters. This is supported by the presence in the pre-Miocene
intervals of mostly argillitic and schisty maximum compacted clay rocks
of predominantly hydromicaceous mineral composition (Barbat. 1961;
Philippi, 1974).
Very specific are the formation conditions of high-salinity “transi-
tional” chlorine-calcium, chlorine-magnesium, sulphate-sodium and
hydrocarbonate-sodium waters localized within productive zones (fault-
blocks) of oil and gas accumulations in the Pliocene sediments. Certain
specifics indicate a hydrogeological environment of mixing different type
water of different stratigraphic belonging (the alkaline formation waters of
hydrochemical background and injected hard waters from the underlying
Miocene complexes). These specifics include their ion-salt composition,
elevated salinity, zonal distribution over individual structures, dominat-
ing association with commercial hydrocarbon saturation and with most
faulted areas of structures in combination with the presence in some fields
of typically Miocene-like hard waters (see above). Mixing modeling indi-
cates that waters in the productive fault-blocks of the Repetto complex are
formation mixes between alkaline background waters and syndepositional
chlorine-calcium waters from the underlying Miocene formations Puente
and Topaga with a fraction of injection hard component (35 to 96%). In
the overlying Pliocene formation Pico the fraction of a foreign ingredient
is obviously somewhat lower (54
80%).
It is typical that maximum share of lower waters is recorded in the
“transitional” chlorine-magnesium and sulphate-sodium varieties; it is
significantly lower in alkaline mixes. Additionally, the depth of the upper
chlorine-calcium and “transitional” water boundary is minimal on the
strongly faulted structures (West Coyote, Long Beach and Santa Fe Springs
fields) and maximal in the fields on less faulted structures (Wilmington,
Huntington Beach, Dominguez). Hence, the extent of injection (inva-
sion height of the Pliocene section by lower waters) is at maximum on the
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