Geology Reference
In-Depth Information
The material composition and the thermophysical properties of the
Mesozoic and Paleogene-Miocene rocks do not differ much over the large
portion of the South Caspian Basin. That is why it is deemed legitimate to
use the quoted “geothermal gradient vs. depth” correlations as the standard
also for the other areas of the region.
There is no need in the use of the temperature gradients to calculate the
temperature for the PT-KT of the basin, as there are reliable direct tem-
perature vs. depth correlations for the depth range from 0.05 to 8.0 km. For
the Azerbaijan portion of the region this correlation is t PS = = 13.7 + 0.149
H 0.716 and for the Turkmenistan portion, t RS = 13.7 + 0.488
H 0.607 .
4.2.2
Estimating Temperature Conditions of Hydrocarbon
Generation in the South Caspian Basin's Sediment Cover
Using the proposed technique, the present-day physical and stratigraphic
position of 135°С isotherm was estimated. This isotherm denotes the com-
pletion of liquid oil generation process (mesocatagenesis substage - М C ,
gradation М C 3 (Kartsev, Vassoyevich, Geodekian et al ., 1971). In the Lower
Kura depression, it covers the Paleogene-Miocene complex (depth interval
5.9-7.4 km). In the Alyat Ridge area, it covers Paleogene-Miocene and 5.5-
6.7 km. In Kobystan, it covers Paleogene-Miocene and 5.
-5.9 km. In the
Baku Archipelago, Paleogene-Miocene and 5.9-7.4 km; on the Apsheron
Peninsula and the adjacent South Apsheron shelf, Paleogene-Miocene and
4.
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-7.6 km. In the Apsheron Archipelago and Apsheron subzone of the
Apsheron-Balkhan Sill, it covers Paleogene-Miocene and 5.0-7.5 km and
Mesozoic at 5.7-7.1 km. In the Balkhan zone of highs, it covers Mesozoic
and 5.5-7.9 km; and in the Gograndagh-Chikishlyar zone, Mesozoic and
5.8-7.8 km.
The deeper Mesozoic sediments occupy a higher temperature range. At
the current stage of the geologic evolution, they generate sequentially the
wet gas and condensate (mesocatagenesis and apocatagenesis substages AC ,
grades MC 4 - AC 2 , temperature 135- 210°С), the late-catagenic methane
(apocatagenesis substage, grades AC 3 - AC 4 , temperature 210-300°С), dry
and acid gases (metagenesis stage MG , temperature >300°C). hese data
indicate that the Mesozoic sediments in the basin practically exhausted their
oil-generating resource at the previous stages of basin's geologic evolution
(during the deposition of the Upper Cretaceous and Paleogene sediments).
Currently over most of the South Caspian Basin, they are generating the gas
phase (including the “dry” and acidic gases), which is “gassing-through” the
entire overlying section.
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