Geology Reference
In-Depth Information
2.
The Paleogene-Miocene Complex
. The thickness of the
Paleozoic-Miocene complex is 2.5 to 5 km. As the tops of
the stratigraphic units composing the complex subsided to a
depth of 0.2 km, the rock and their organic matter underwent
diagenesis. Upon reaching the 0.2- to 1.18-km depth interval,
they entered the protocatagenetic substage (
PC
1
- PC
3
grade).
Then followed the
MC
1
grade of the mesocatagenesis sub-
stage at 1.8 to 2.7 km; the
MC
2
grade, at 2.7 to 6.1 km; the
MC
3
grade, at 4 to 7.6 km; the
MC
4
- AC
2
grade, at 5.3 to 9 km;
and the
AC
3
grade, at 10.4 to 11 km.
Correspondingly, during the Middle-Pliocene age (PS/
RBS) the generation of biochemical and early-catagenic
gases in these sequences had been practically complete.
The rocks had entered the oil generation zone since Middle
Pliocene time, and the wet gas and condensate generation
environment, since Late Pliocene-Early Quaternary. Deep
methane generation occurred during the Quaternary time.
The current status of the Paleogene-Miocene complex,
depending on depth and temperature environment, is that
of the oil, condensate, wet gas, and, in part, late-catagenetic
methane gas generation, i.e., it is producing all hydrocarbon
types and phases (Table 6.2).
3.
The Pliocene-Quaternary Complex
. The Pliocene-
Quaternary Complex generated hydrocarbons during dia-
genesis, and proto- and meso-catagenesis (substages
PC
and
MC
, grades
MC
1
, and, in part,
MC
2
). The biochemical and
early-catagenic gas generation occurred within the subsid-
ence range of tops of composing parts of complex at 0.03 -
0.2 and 0.03 - 2.7 km. The beginning of oil generation (
MC
1
)
occurred when the deposits subsided to a depth of 1.6 - 4.1
km, whereas the oil window (grade
MC
2
) occurred at 2.6 to
6 km (Table 6.3).
The basin's sediments are relatively weakly heated (thermal gradient
does not exceed 22.7
C/km; Rachinsky, 1983). This supports the results
of coal petrography study by Dmitriyeva and Parparova (1981). These
scientists found that the dispersed organic matter in the Miocene clayey
sandstones at 3.8 km is just at
PC-B
stage (vitrinite refractance of 1.696;
the Duvanny Field in SE Gobustan). The clayey sandstones of Zyrya field
(Apsheron Peninsula) at a depth of 4.86 and 7 km were, respectively, at
PC-B
and
D-MC
1
stages. The Productive Series (Bulla Deniz, Hamamdag
°
