Geology Reference
In-Depth Information
3.2.1 Intermontane Depressions
3.2.1.1
The South Caspian Depression
A typical and important feature of the Meso-Cenozoic sediment cover in
the South Caspian Basin is the commonality of abnormally-high pore (in
the impermeable or low-permeability intervals; clays and argillites) and
formation pressure (in clastic and carbonate reservoirs). Zones and areas of
their manifestations are found in different stratigraphic complexes, vary in
the section and area-wise in their intensity, generation mechanisms, pres-
ervation and relaxation conditions and the extent of hydraulic communi-
cation with regional hydrodynamic system and local waterhead complexes.
The information base of our study includes the following:
t
over 2,500 field measurements of the initial formation pres-
sure at 206 prospects under appraisal;
t
petrophysical determinations of AHPP gradients by the
techniques of normal compaction curves and equivalent
depths in 300 wells;
t
interpretation of field seismic, gravimetry, electric and mag-
netic surveys and acoustic sounding;
t
drilling materials on a great number of exploratory and
appraisal wells
5
;
t
our confidential, reference and published data on the geo-
logic structure of regions and local structures, rock lithology,
geologic history, regional hydro-geodynamics, hydro-geo-
chemistry and so on.
The basin's Mesozoic sediments are identified from the materials of core
and exploratory/production drilling and rare tests and studies in wells
mostly from remote, most-uplifted peripheral parts of the basin. The lat-
ter include a number of structures over the southeastern plunge of the
Caucasus Major meganticlinorium, in the North-Apsheron zone of highs,
eastern plunge of the Balkhan zones, offshore portion of the Resht and
onshore portion of the Gogran troughs (Table 3.2).
5
Drilling materials (mud weight dynamics and the data on complication in drill-
ing) were used for pressure estimation only in uncased wells and intervals where
the objectives have not been tested. In the environment of actual data scarcity
(especially for the practically non-prospective Mesozoic and Paleogene-Miocene
complexes) such approach was viewed as imposed and sufficiently justified as it
allowed for a rough quantitative estimation of baric parameters of the structures.
