Geology Reference
In-Depth Information
in various sedimentary section components and of “sliding” due to a
decreased friction of the competent bocks against the upper and lower sur-
faces of the adjacent incompetent rocks (dilatancy
3
) as a result of orogenic
stress. These tectonic deformations were transferred into the overlying
and underlying intervals with the formation of projected structures (drape
folds, stamp folds, sag synclines, etc.). They also determined regional for-
mation of tabular, overthrust and nappe folding, which account for the
mismatch in the structural plans of different stratigraphic complexes. They
are accompanied by cleavage and intense manifestation of mostly fault tec-
tonics, by diapirism and mud volcanism, which in their turn are accompa-
nied by deformations, most commonly faults.
Syngenetic AHFP
in the reservoirs may form in several ways, and may
be due to several factors:
t
Artesian pressure difference (piezometric level difference in
charge areas, waterhead generation and discharge of infiltra-
tion geo-hydrodynamic systems).
t
Secondary
pore
space
cementation
by
mineral
new-formations.
t
Manifestation of aquathermal effect and thermoelastic
regime of the subsurface (differences in heat expansion fac-
tors between rocks and water).
t
Presence in the compensated-subsiding lens-shaped reser-
voir beds with significant clay content due to the release by
these clays of additional pore fluid volume during compac-
tion and dehydration.
t
Nonuniform compression at neotectonic motions of closed-
elastic spatially-restricted natural reservoirs.
t
Increase in the hydrocarbon volume in accumulations at
their thermal degrading during subsidence.
Following are the diagnostic attributes of syngenetic AHFP:
t
Commonality of abnormal pressure over the area (including
inter-structural portions).
3
Dilatancy is “rock swelling due to the underground water pressure increase -
assumed precursor of an earthquake”. Another definition: “a phenomenon caused
by the nature of the stacking or fitting together of particles or granules in a hetero-
geneous system, such as the solidification of certain soils under pressure, and the
thixotropy of certain gels”.
