Geology Reference
In-Depth Information
The duration of deposition during the Mesozoic time was 121 MMY
with the depositional rate of 37 to 91 m/MMY, whereas the duration of the
Paleogene-Miocene deposition was 56 MMY with the depositional rate of
36 to 89 m/MMY.
A different situation existed during the Pliocene-Quaternary time, char-
acterized by:
1. Avalanche deposition (437-750 and even as high as 900 m/
MMY).
2. High intensity of basin's subsidence.
3. “Jumping” of oil and gas source rocks (including the upper
portion of Paleogene-Miocene complex) through the gen-
eration zones of corresponding fluids.
4. Partial “freezing” (conservation) of oil and gas generation
potential of generating zones.
5. Depth-wise “stretching” of these zones.
6. Release by the rocks of fluids not matching (in terms of their
composition and phase behavior) the depth and thermal
position of hydrocarbon-generating sequences.
Because of its peculiar lithophysical composition, the Paleogene-
Miocene interval proceeds in the same direction. This interval consists
mostly of clay facies and has severe baric environment with coefficient of
AHPP's
3
of up - 1.70 to 1.95 (Tables 6.1-6.3, Rachinsky, 1977).
The combined effect of the latter two factors impedes chemical reac-
tions within the complex whereby the dispersed organic matter is con-
verted to hydrocarbons. The impediments are substantial limitations in the
amount and rate of outflowing products, “freezing” (conservation) of oil
and gas-generation potential and its implementation within the vertically-
expanded depth and temperature range.
Table 6.4 shows the hydrocarbon generation temperature and depth in
the South-Caspian Basin using catagenic scales of Kartsev
et al
. (first lines
of cells) and of Waples (second lines of cells).
The validity of this conclusion is supported by the extremely elevated
bitumen content in the Paleogene-Miocene clays and the common
3
AHFP is the abnormally high formation pressure, whereas AHPP is the abnormally high
pore pressure.
