Geology Reference
In-Depth Information
In order to suggest formation pressure absolute values in the zone of
extreme AHFP manifestation, we will list actual data for some appraisal
prospects in the central anticlinal zone of the Baku Archipelago. At the
Garasu prospect in near-OWC well 25 while testing VII th horizon of PT
(interval 4,855-4,861 m MD), after water injection the built-up pressure at
the wellhead was 21.0 MPa. Considering that some amount of oil was in the
borehole and assuming the well emulsion density at 0.800 g/cm 3 the for-
mation pressure may be about 60 MPa, and its excess over the hydrostatic,
11.4 MPa with К AHFP =1.234. At the nearby (to the south) prospect Sangi-
Mugan in a crestal well 15 testing of the same bed (MD 4,581-4,590  m)
produced flow of water at 570 CMD. When the well was shut-in, pressure
at the wellhead was 20 MPa. This gives the formation pressure estimate of
65.85 MPa with К AHFP =1.436. On the next structure south (Aran-Deniz)
in a crestal well 7 testing of the same horizon (interval 4,372-4,377 m)
yielded a flow of the formation water at a rate of 1,500 CMD with the well-
head pressure in the shut-in well of 40 MPa. That gives an estimate of the
formation pressure of 83.75 MPa with К AHFP =1.915 (Aliyev et al ., 1976). At
the Sabail prospect (same anticlinal zones but somewhat southward) well 1
tested the same horizon at MD=5,972-5,975 m. The formation water flow
was 650-700 CMD and wellhead pressure, 34.3 MPa. Measured forma-
tion pressure was 94.3 MPa, К AHFP =1.574. Well INX-1 at the Inam pros-
pect somewhat southwest was stopped at TD 4,442 m despite weighting
the drill-mud to 2.30-2.40 g/cm 3 due to high AHPP. The sidekick was also
unsuccessful so the well was plugged and abandoned.
Drilling was difficult at a number of closely positioned pros-
pects (Ateshgyah, Yanan Tava, Kyurdashy, Araz-Deniz, Talysh-Deniz,
Nakhchyvan and Zafar-Mashal). While drilling, in all these wells were
continuously recorded intense water and gas shows and blowouts threat-
ening to convert to open flow, drastic increase in drilling rate in some
intervals, and mud circulation loss. In the Baku Archipelago (prospects
Aran-Deniz, Sangachaly-More, Duvanny-More and others) the intensity
of abnormality manifestations drastically declines in the direction from
the structure crests to the periphery and is spatially associated with most
faulted areas (where the so-called “crestal” water is developed - Rachinsky,
1989). The water is allochtonous with the enclosing sediments, local
temperature and hydrochemical distortions (of the cross-flow-injection
nature) of the corresponding areas (Rachinsky and Muradian, 1977;
Rachinsky, 1989, 1990).
The aforementioned AHFP development in the region is controlled by
the reservoir parameters and lithofacies. At the same time, it is closely asso-
ciated with their geologic evolution, the nature and direction of neotectonic
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