Geology Reference
In-Depth Information
proceeded, the amount and outflow rate of the squeezed-out fluids became
insignificant as they could not overcome hydraulic resistance of the
medium and maintain for an extended period the lateral flow of subsurface
waters from the deepest zones of basins to their flanks.
Kublicki (1973) found that favorable conditions for neoformation of
SiO
2
, calcite, sulfates, etc., are created near the contact of “undercom-
pacted” clays with reservoirs, which drastically decreases the permeability.
Thus, the emigration of pore fluids from the clay sequences into permeable
reservoirs becomes more restricted.
This conclusion was supported by Bloch (1969) and Bondarenko (1973),
who found that the pore water in clay systems possesses unusually high
dissolving capacity. In particular, the silicon content in the anomalous
water exceeds the solubility and precipitates, plugging the pores (Spitsin
et al
., 1972).
All of the above-discussed factors indicate that the amount of water
squeezed-out of clays per unit time is much lower than that calculated
above.
Relationships between the porosity and permeability and permeabil-
ity and depth for clays were given by Mukhin (1965) and Neglia (1979)
(Figures 3 and 4).There is rather low permeability at depths below 500 m
(less than 0.01 millidarcy) (Dobrynin and Serebryakov, 1978; Linetsky,
1974).
Kidwell and Hunt (1958), who studied the compaction of young clay
deposits in the Orinoco Delta (Venezuela), found that abnormally-
high pressures (15 to 20% over the normal) form at a depth as shallow
as 30 to 40 m due to a slow water outflow from the compacting clays.
Similar phenomena are observed in the case of hydrotechnical construc-
tion (Rachinsky and Durmishyan, 1982; Rachinsky and Kerimov, 1989;
Ulitin, 1955).
Below a depth of 500 m, the fluid outflow from clays becomes less intense.
It takes a much longer time, and the controlling mechanisms are differ-
ent and include diffusion, capillary, film and osmosis (Rachinsky, 1983).
Baturin (1954) stated that the sedimentogenic waters are squeezed from
clays down to a depth of 400 m and Lomtadze (1954) and Strakhov (1962)
restricted this interval to 400 to 800 m (also see Rieke and Chilingarian,
1974). This suggests that the elision flow of the subsurface water from deep
central parts of basins toward their periphery is limited because the water
release from clays at these depths is negligible.
One should also consider the fact that water can be supplied by dia-
genetic transformation of montmorillonite to illite (dehydration process)
