Geology Reference
In-Depth Information
the regional geo-fluid-dynamic system functioning suggests preliminary
solution of several major issues. These issues are the determination of clay
sequence compaction conditions and outflow from them of compressed
fluids as the major agent in the elision water-exchange; and finding the
correspondence degree between the actual patterns in spatial distribution
of normalized formation pressure gradients and some theoretical fluid-
dynamic regimes.
5.3.1
Compaction of Clays as a Factor in the Formation of
Geo-Fluid-Dynamic Regime
Compaction of clays is an important factor defining the hydrodynamic
regime in deep horizons, facilitating the formation of abnormally high
pore pressure (AHPP) and abnormally-high formation pressure (AHFP)
and causing hydrocarbon emigration, migration and accumulation.
The phenomenon had been reviewed in numerous publications by Athy
(1930a, 1930b), Hedberg (1926, 1936), Weller (1959), Dickinson (1951),
Chilingarian and Wolf (1975, 1976), Chilingar and Knight (1960), Hubbert
and Rubey (1959, 1960), Burst (1969), Powers (1967), Magara (1968),
Mukhin (1968), Rieke and Chilingarian (1974), Vassoyevich (1960) and
others. Substantial amounts of laboratory studies of cuttings and core sam-
ples, geophysical and oilfield observations and theoretical studies did not
result in the complete elimination of discrepancies in the interpretation
of the compaction phenomenon by different scientists. Especially impor-
tant are discrepancies, related to regional hydrodynamics; in particular, the
qualitative and quantitative evaluation of the natural hydraulic-head sys-
tems at great depths under the conventional elision
4
scenario and the role
4
Infiltration basins
are subsidence areas within tectonically stable regions, mostly
platforms. They represent relatively shallow depressions with the artesian hydro-
dynamic regime. Typical examples are platform depressions of Russia, such as the
Moscow, N. Dvina, Vyatka-Kama syneclises, Angara-Lena depression, Kyzylkum
depression of the Central Asia and others. They usually have relatively thin sedi-
ment cover (2 to 3 km), which reflects sluggish tectonic regime and the proclivity
to epeirogenic motions.
The sediment cover of these “tectonic bowls” is usually uncovered by erosion.
Vadose waters from the surface penetrate the reservoir rocks and migrate to the
discharge areas where the most permeable beds are cut-in by rivers. The intense
movement of the infiltration waters occurs in the shallow section. Down the sec-
tion, the water exchange becomes slower, which reflects in the underground water
composition.
