Geology Reference
In-Depth Information
One can estimate the excess volume of pore water giving rise to syn-
genetic AHPP in the clay sequence. Tables 5.2 and 5.3 are based on the
assumption that clay compaction follows the Weller's curve, which cor-
responds to the normal hydrodynamic regime. These tables refer to the
central South-Caspian Basin. The values presented were compared with
the actual values, which are typical for the areas with maximum AHPP
(Rachinsky, 1977, 1982, 1983). This comparison shows that within the first
subsidence interval the excess pore water volume responsible for the emer-
gence of AHPP is 5,000 km
3
, within the second subsidence interval is 6,500
km
3
, and within the last one, 17,300 km
3
. The writers did not calculate the
fluid outflow for the subsequent subsidence intervals because the fluid out-
flow there practically stopped.
As far as the lateral migration of squeezed-out fluids is concerned, the
directional subsurface water flow from the basin's center to its periphery is
unlikely. Even with the grossly overstated water-head gradient of 0.1 m/m,
the estimated volume of squeezed-out water would take, depending on the
clay sequence subsidence interval, 16,333 and 400 MMY to migrate over
a distance of 10 km. These durations are much longer than the age of the
compacted rocks. Thus, the central part of the South-Caspian Basin could
not have been the source of feeding an elision system. Consequently, it
could not have been the major hydrocarbon supplier to the oil- and gas-
accumulation zones of basin's flanks.
In order to examine the possibility for elision regime to emerge during
the development of South-Caspian Basin's sandy-clayey Pliocene facies,
the following assumptions have been made:
1. The thickness of the section = 2,500 m.
2. The thickness of clays under compaction = 1,500 m.
3. Areal extent of the facies = 90,000 km
2
.
4. The volume of water buried in the reservoirs = 27,000 km
3
.
5. The discharge amount (in the form of mud volcanoes,
upwelling thermal sources, salt lakes, subsurface water dis-
charge at surface as springs, and discharge into the seawater)
= 9.0*10
−
3
km
3
/year.
For the basin's east flank, the present-day discharge from the Middle
Pliocene deposits is 3*10
−
3
km
3
/year (Kolodiy, 1969), whereas for the west
flank the estimate is 6*10
−
3
km
3
/year.
The discharge amount for the entire post-Miocene interval (about 13
MMY) was close to 117,000 km
3
, which is four times higher than the sub-
surface water reserves in the reservoirs. The 90,000 km
3
deficit of water
