Geology Reference
In-Depth Information
depending on the region, is 7-8 to 24-26 km thick. The thickness reaches
its maximum offshore (South Apsheron Trough and the Baku Archipelago).
The section includes three distinct lithofacies.
The lower stage is composed of clastics and carbonates of Mesozoic age
(Lower and Middle Jurassic through the Upper Cretaceous) having a thick-
ness of 4.5 to 11 km. Mostly clayey middle stage is of Paleogene-Miocene
age (Danian-Pontian) with a thickness of 2.5 to 5.5 km. The upper stage
includes alternating Middle Pliocene through Quaternary clays and sands,
thickness of which is 6 to 7 km.
Average depositional rate of the Mesozoic cycle was 37 to 91 m/MMY;
of the Paleogene-Miocene cycle, 38 to 69 m/MMY; and of the Pliocene-
Quaternary cycle, 375 to 900 m/MMY.
Average present-day geothermal gradient, depending on the area, is
19.1 to 22.7
°
C/km. Temperature of the basement surface ranges between
287
C
in the Baku Archipelago at a depth of 21.5 km. Average pore- and forma-
tion-overpressure (AHPP and AHFP) coefficients are: 1.35 to 1.58 in the
Mesozoic, 1.70 to 1.95 in the Paleogene-Miocene, and 1.04 to 1.53 in the
Pliocene-Quaternary deposits (Table 6.1-6.3).
A thorough study of the basin's oil and gas-generation potential using
the chemical-bituminological, coal petrography, gas chromatography and
isotope techniques was performed by Korchagina
et al
. (1988). It con-
cluded, based on core samples (to a depth of 6.3 km) and mud volcano
ejecta (assumed depth of 8 to 10 km), that potential Meso-Cenozoic source
rocks include clayey limestones, marls and clays. They contain moderate
concentrations of syngenetic OM mainly of aline series. The TOC content
in sands and limestones is 0.02 to 0.2%, and 0.4 to 0.8% in clayey rocks.
Some Oligocene-Miocene and PS/RBS members (Maikopian Fm.) have up
to 4% TOC. The rock-eval data indicate low initial potential of 0.65 kg/
ton in the rocks of Upper Cretaceous, 0.24 in the Eocene rocks, 2.4 in the
Maikopian rocks and 0.3 in the PS/RBS.
It was determined that the insoluble dispersed organic matter (DOM)
in the Upper Cretaceous, Eocene and Maikopian rocks is at the meso-cata-
genetic stage (MC), and in PS/RBS, mostly at the proto-catagenetic stage
(PC). The following facts have been established:
°
C over the Apsheron-Balkhan Seal at a depth of 12.5 km and 424
°
1. Monotonous decrease of the initial potential (
H/C
atomic
)
down the section: 1.2-1.4 in PS/RBS (the liptinite field of the
van Krevelen diagram modified by Hunt) to 0.8 - 1.1 in the
Maikopian-Eocene rocks to 0.6 - 0.8 (vitrinite field) in the
Upper Cretaceous rocks.
