Geology Reference
In-Depth Information
water- and oil-gas shows were observed. They were mostly associated with
discontinuous thin sand interbeds with AHFP. Most demonstrative cases
include:
t
The oil blow up in testing well 534 (Duvanny-More pros-
pect), which caused abandonment of the well.
t
Strong gas-water show in well 6 (Yuzhnaya-2 prospect),
which turned into a short-duration open flow.
t
Strong gas show from a depth of about 2 km while drilling
well 1-Shimali Apsheron (Bagir-Zadeh
et al
., 1988).
There is no large-scale commercial oil and gas production from
the Miocene-Oligocene sediments of the region. Rare exceptions are
Umbaki, Ajiveli, Karadagh, Shabandagh, Shubany, Karaeybat, Binagady-
Chakhnaglyar, Sulutepe, Masazyr and Artem Isl. prospects. Small sporadic
oil and gas accumulations in thin reservoirs were discovered there. They
are positioned in strongly faulted crestal areas of highs. The highs are com-
monly located close to surface exposures of these rocks or in the areas of
their shallow depth and are always associated with same-name mud volca-
noes and hills. These reserves are insignificant and of insignificant resource
value.
While drilling through the Oligocene-Miocene complex significant
excess of the pore pressure over the hydrostatic was identified in clays. In
a small number of areas where these deposits are exposed on the surface
(Northwestern Apsheron, North-Apsheron zone of highs and Southern
Kobystan) they underwent lengthy discharge. Only their normal pressures
are recorded. But even in these cases with increasing depth to the interval's
top and at depths the frequency of occurrence of members with AHPP
continuously increases. That significantly complicates drilling and requires
drastic weighing of drilling fluid.
Typical example is the Umbaki prospect (Kobystan). The sediments of
the Diatomaceous Formation and the Chokrackian Horizon are exposed
there on a significant territory. Drilling through these intervals in all wells
of the crestal zone (in the rock exposure areas) was conducted with normal
mud. However, already in the Lower Chokrackian section and especially
in the underlying Maikopian Formation rather intense AHPP manifes-
tations were recorded while drilling. They strengthened with depth and
with distance from discharge zones. In wells over deeper areas of the struc-
ture (on the flanks and plunges) the abnormality showed up immediately
upon penetration of the uppermost part of the section (the Diatomaceous
Formation).
