Geology Reference
In-Depth Information
in all other stratigraphic intervals of the sedimentary section have been
discovered by individual wells on a limited number of prospects. They are
sporadic and of minor commercial value.
Certain patterns have been identified in the hydrocarbon accumulation
occurrences of the PT-KT. They may be summarized as follows:
1. The discovered accumulations form three zones differing
in the phase state of their hydrocarbons. The upper zone
(weighted average depth, 480 m) is of a smaller significance
due to its strong deformations; the accumulations are mostly
gas. The middle zone includes mostly oil accumulations
at the weighted average depth of 1,350 m. The lower, gas-
condensate zone has average weighted depth of 4,500 m.
2. The oil and gas accumulation zones are controlled by the
major faults and are spatially associated with them.
3. As the folded system gradually dips to the center of the basin
and as the local structures become less faulted, oil and oil-
gas accumulations give place to gas-oil and gas-condensate
accumulations.
4. The section's gas-saturation increases with depth (both
stratigraphic and physical).
5. Over 80% of the discovered accumulations are found within
the depth interval at depths to 3.5 km.
The largest fields in the South Caspian Depression are: onshore,
Balakhany-Sabunchi-Ramany, Surakhany, Bibieybat, Kyurovdag, Cheleken,
Koturtepe, Barsagelmes; offshore, Neftyanyye Kamni (“Oil Rocks”),
Gyuneshli, Chirag, Azeri, Shahdeniz, Sangachaly-More- Duvanny-More-
Bulla Is. (Figure 1.3).
1.1.2
The Padan Depression
The depression is the western portion of the Adriatic oil and gas basin. It
is positioned between the folded Alpine and Apennine mountains and is
open eastward, toward the Adriatic Sea (Figure 1.4). The section includes
thick Permotriassic (up to 5,000 m), Jurassic (up to 400 m), Cretaceous
(up to 500 m), Paleogene (up to 3,700 m), Neogene (up to 8,500 m) and
Pleistocene (up to 3,000 m) deposits. Two lithostratigraphic complexes are
identified within the sediment cover: the carbonate Eocene-Mesozoic and
the clastic Oligocene-Quaternary. A typical feature of the clastic series is
its drastic facies variability causing the formation of lens-shaped reservoir
