Geology Reference
In-Depth Information
K
anom
1.70
1.60
1.50
1.40
1.30
1.20
1.10
10 20 30 40 50 60 70 80
C
, %
Figure 3.8
Formation pressure abnormality factor vs. permeable/impermeable rocks
ratio. Intermontane depressions: Пв, Padan; ЮКв, South Caspian; Вв, Viennese; ИрАв,
Irrawaddy-Andaman; ЛАв, Los Angeles; Мв, Maracaibo; foredeeps: Пкп, Carpathian;
ИКп, Indolo-Kuban; ТКп, Tersk-Caspian; Пзп, Zagros.
Intense and extreme AHPP manifestations require the application in drill-
ing of heavily weighted drilling mud (density over 2.2 g/cm
3
). Positioning
of such manifestations in the development areas of nappe tectonics and in
undercompacted subthrust clay members testifies to their mostly syngenetic
origin caused both by neotectonic compression of incompetent sequences
and by limited outflow of pore fluids in the process of consolidation.
Reservoir intervals in the internal zone of the Carpathian Trough
commonly have AHFP. Abnormality factor there is most commonly
1.5-2.1 (Zinenko, 1975; Kolody, 1983; Novosiletsky, 1975; Orlov, 1980).
Abnormally-high formation pressure is recorded practically on all anti-
clines of the Borislav-Pokut Anticlinorium, which are sealed at the top
by the thick Lower Miocene salt sequence (Starynya, Gvizd, Bitkov,
Dobtogostov, Rosilnya, Kosmach and others). Formation pressure in the
Menilite Series of the Rosilnya Field exceeds the hydrostatic by the factor
1.6, in the Eocene, 1.5, in the Paleocene, 1.3. At the Kosmach prospect the
abnormality factor in the Paleocene-Eocene sediments is 1.47, at the Luga
Prospect (at depth of 6,200 m), 1.6 (Kolody, 1975).
The formation pressure ranges are significant. In different fault-blocks
even of the same structure, it reaches over 10 MPa and is even greater between
individual structures. Reservoirs with pressure so diverse are isolated.
Regionally the formation pressure slightly declines northeast to south-
west toward the Carpathian Mountains, i.e., with distance from strongly
deformed zones of the Stebnik overthrust.
