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corresponded with syngenetic AHPP and low intensity combination (syn-
and epigenetic) AHFP. Wellhead pressure in shut-in wells did not exceed
7 MPa; water rate was usually no greater than 20 CMD. For instance, at
the Gyadysu prospect (wells 21 and 42) the excess formation pressures at
MD=1,000 and 1,070 m (Cenomanian) were 3 and 5 MPa and К AHFP =1.30
and 1.42, respectively, (Rachinsky, 1973).
On the other hand, the Santonian-Danian interval includes undercom-
pacted plastic clay members. In the wells, regardless of their position on
the structureе, was recorded continuous intense swelling/blowout sup-
pressed by using heavy mud (up to 1.75 g/cm 3 and greater). here were
also elevated cutting and rock fragment recovery, continuous drillstring
overpull and sticking, clay plugs push-out from the borehole, etc. These
are indications of dominating intense syngenetic AHFP and AHPP. They
were generated due to paleo- and present-day gravity consolidation of
clays at conditions of obstructed pore water outflow and multidirectional
paleo- and neotectonic stresses with some migrational epigenetic compo-
nent. Examples of AHFP in the reservoirs of this interval are the data from
two offshore prospects. At the Khazri prospect (North-Apsheron zone of
highs) in well 4 at MD=4,318 m, the measured formation pressureе was
68.5 MPa and its excess over the hydrostatic was 25.3 MPa with К AHFP =
1.59 (Rachinsky and Muradian, 1977). At the Enzeli-More prospect (well
Khazar-1) drilling of the interval 4,410-5,570 m was possible only with
heavy mud of up to 1.95 g/cm 3 (Yusuf-Zadeh et al ., 1992).
he Paleogene-Miocene sediments 10 in a typical schliere facies are ubiq-
uitously developed in the South Caspian Basin. They are often exposed
in diapir piercement plugs on denuded structures and in the eruption
cores of mud volcanoes [Kobystan, Apsheron Peninsula, the western por-
tion of Apsheron-Balkhan Sill (Zhiloy Isl., Neftyanye Kamni)]. There,
they are represented by compact lithological varieties. In the area of
its deep occurrence the complex is composed of thick (up to 3-5 km)
mostly montmorillonite clays. The clays are weakly compacted, with high
water-saturation, plastic, with rare thin lens-shaped siltstone and sand-
stone interbeds and beds (total clay content of the section is 90-95%).
The sequence was deposited during an immersion cycle of the region's
geologic evolution (see Table 3.2).
he Paleogene interval ( Paleocene and Eocene sediments; under the
local nomenclature, correspondingly, the Sumgait and Koun formations)
10 Paleogene-Miocene sediments in the South Caspian Basin in most cases have
not been an independent exploration target and were reviewed when drilling for
the Mesozoic.
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