Geology Reference
In-Depth Information
t
Nonuniformity in the abnormality distribution among indi-
vidual adjacent fault-blocks and areas.
t
Practical nonexistence of the increase in pressure abnormal-
ity down the section within inter-structural zones.
Along with epigenetic AHFP their syngenetic modifications are also
common in PT-KT. They were caused by:
t
Smectite dehydration in clayey portions of the section. It
proceeded together with lithostatic compaction of the rocks
under the weight of overburden at temperature over 105
°
C
and was accompanied by the release of additional consti-
tutional water in the constant volume of matrix pore space
(Burst, 1969; Fertl, 1972).
t
Multidirectional compression of natural reservoirs under
the neotectonic stress.
The latter occurs in the areas and intervals where PT-KT section is
composed of a clayey (silty) lithofacies (Lower Kura Depression, Baku
Archipelago, Kobystan, offshore eastern portion of the Apsheron-Balkhan
Sill, Gograndagh-Chikishlyar zone of highs, Fore-Elbrus trough, South
Caspian deep depression) and clay content reaches 98% with totally clayey
individual intervals (such as the Surakhany and Sabunchi formations in
the Baku Archipelago).
The syngenetic AHFP in the aforementioned areas is responsible for
regional manifestations of abnormal pressure in them and causes a sub-
stantial increase in epigenetic AHFP outside the accumulation outlines.
In other words, abnormally high formation pressure in highly clayey low-
permeability reservoirs is the total of the two components. One of them is
epigenetic AHFP. It is generated by vertical high-pressure fluid crossflows
from the underlying deposits. Another one is syngenetic AHFP, caused by
continuing gravity compaction of rocks, montmorillonite dehydration in
the clay varieties of the section and its neotectonic compression.
This conclusion is supported by materials on the Southwestern
Turkmenistan. There, no AHFP is identified in the entire penetrated KT
(Red-Bed Sequence) section of the Kelkor Trough. Abnormal pressure
in the reservoir-overlying beds and in the Akchagyl and Apsheron Stage
accumulations is not recorded over the entire east flank, although their clay
content exceeds the average for the Upper Pliocene deposits and is com-
mensurate with clay content of the Lower Red-Bed rocks and their depths
are 500 to 3,500 m. Should have AHFP originated only by the gravity load,
