Geology Reference
In-Depth Information
2. Prevailing autochthonous bitumoids in PS/RBS to a depth
of 3.3 km replaced down the section by a drastic increase in
frequency of their residual and migrated varieties.
3. High concentration of high-temperature boiling hydrocar-
bons in the PS/RBS bitumoids (1.56 to 16.4 kg/m3), indicat-
ing an epigenetic origin.
4. Good correlation between the yield of liquid and gaseous
hydrocarbons and the catagenic alteration stages of OM
(Korchagina
et al
., 1988).
These data support the view of the oil, gas and condensate generation
in the Meso-Cenozoic section of the South-Caspian Basin, in accordance
with the scheme of N.B. Vassoyevich as modified by Kartsev
et al
. (1971)
and Vassoyevich
et al
. (1979).
This concept is based on the consecutive generation process of the mate-
rially and phase-wise different fluids. The process proceeds as follows:
t
Gases of biochemical origin: diagenesis (temperature
<20
C).
t
Early catagenetic methane: proto-catagenesis (PC; tempera-
ture of 20 to 60
°
C).
t
Oil: meta-catagenesis (MC; MC
1
-MC
3
, temperature of 60 to
135
°
C).
t
Wet gas and condensate: meso- and apo-catagenesis (AC;
MC
4
-AC
2
, temperature of 135-210
°
C).
t
Late-catagenetic methane: apo-catagenesis (AC
3
-AC
4
grades,
temperature of 210-300
°
C).
t
Dry and sour gases: metagenesis (MG; temperature >300
°
°
C).
Considering the spatial/temporal geotemperature dynamics as a func-
tion of geological evolution in the specific areas, one can use the geother-
mal reconstructions for a quantitative estimation of the geochronological,
stratigraphic and depth ranges for the implementation of basin's initial
hydrocarbon potential.
The task may be accomplished by calculating the present-day and paleo-
depths with the temperature ranges corresponding to the grades of organic
matter alterations. This may be done through the actual correlation of
each cycle of basin's geological evolution with the corresponding depth
(Rachinsky, 1983).
This approach involves the determination of temperature, temperature
gradients, and their correlation with depth at the deposition time of each
