Geology Reference
In-Depth Information
These additional factors are:
t
The generation of syngenetic AHFP component directly in
the reservoirs of water-saturated interval due to the release
of the pore water by clayey varieties that continue to consoli-
date in the process of sediment subsidence.
t
Nonuniform reservoir compression under the neotectonic
motions.
t
AHFP “injection” in the reservoirs under regional barriers.
The specific feature in all cases of the stated deviations, which supports
the legitimacy of such judgment, is their constant association with spatially-
restricted lens-shaped clayey reservoirs, closed-elastic, with restricted
water-exchange, positioned in subsiding thick
Neocomian sequences of
neotectonically active regions or directly underneath the hydrodynamic
seals.
Based on analysis of all data quoted in this Chapter:
1.
Abnormally high pore pressure (AHPP) in clay sequences
of Alpine mobile belt regions is mostly of syngenetic
origin. It is caused by the restriction of fossilized paleo-
compressed pore fluid outflow in the process of continu-
ing consolidation of incompetent formations, their elastic
compression in neotectonic processes and clay minerals
dehydration at high temperature. When such incompetent
formations serve as seals for hydrocarbon accumulations
of substantial height, over syngenetic AHPP is superposed
epigenetic component identified by a halo invasion into
the clay pore space of high-pressure fluids from the under-
lying accumulations.
2.
Abnormally-high formation pressure (AHFP) in reservoirs
of upper structural stages is most commonly of epigenetic
origin and is associated with injection of high-pressure
fluids from lower intervals of the sedimentary section.
Generation of syngenetic AHFP in these lower intervals
occurs as a result of the formation in a high-temperature
zone of water from the dehydration of minerals, of second-
ary mineral-formation mechanisms, baroeffects from dif-
ferences in fluid and enclosing rocks expansion with the
mandatory participation of elastic compression of the natu-
ral reservoirs due to neotectonic stresses.
