Geology Reference
In-Depth Information
3.2.2.3
The Tersk-Caspian Foredeep
AHPP is discovered in clay members of the Maikopian Series through
Middle Miocene and AHFP, in all intervals of the stratigraphic section
(Triassic through the Middle Miocene; Table 3.7, Figure 3.11).
AHPP manifestations in drilling include:
t
Swelling/blowouts, release of abundant amount of cuttings,
push up of the drill-string, etc., are recorded at all prospects
regardless of well structural position and are associated with
thick clay members of abnormally high porosity.
t
Consistently high AHPP levels of the clay sequences' maxi-
mum thickness.
t
Diapirism and formation of nappe tectonic forms in the
incompetent plastic complexes.
These are all the indications of their mostly syngenetic nature caused by
a restricted outflow of the pore fluids from clays in the process of their con-
solidation by the generation of regenerated water and elastic compression
of clay sequences through the neotectonic stress (Durmishyan, Muradian
and Rachinsky, 1974; Orlov and Kornilov, 1986).
In individual fields (Karabulak-Achaluki, Staro-Groznenskoye,
Zamankul and Braguny) the Maikopian sediments directly overlying pro-
ductive Upper Cretaceous reservoirs display high excess pressure. There,
syngenetic AHPP component is superposed by epigenetic component,
which occurs due to the penetration of high-pressure fluids from the
underlying accumulations into the pore space of clays. The integral effect is
the generation in clays of AHPP at geostatic level with abnormality factors
of about 2.0-2.4.
Maximum AHFP manifestations over the region are associated with
weakly deformed buried structures of the Priterek zones (Pravoberezhnaya,
Chervlennaya and other prospects) and local traps in zones of the accom-
panying folding, i.e., the structures modifying troughs that separate and
fringe the Tersk and Sunzha anticlinal lines (Northern Malgobek, Gorskoye,
Mineralnоyе, North-Mineralnоyе, Andreyevskoye, Mezhkhrebtovoye and
West Gudermes fields). On stronger faulted highs of both lines, the abnor-
mality factors are much lower. This determines the functional association
of AHFP with drainage conditions of natural reservoirs. Conclusions are
based on the data for the individual local highs' fault-blocks subjected
to different hydrodynamic environment. These data show clearly mosaic
waterhead distribution. For instance, the range of normalized levels in
