Geology Reference
In-Depth Information
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The basin's regional geothermal field has clearly a mosaic
nature, which corresponds with its step-block architecture
and with differences in lithofacies composition of the section
in individual regions. At the same time, the actual tempera-
ture distribution at different subcrops and over the area of the
region, together with the aforementioned affecting factors, is
not contradictory with the concept of functional correlation
between the temperature at the subcrops and the closeness
to the surface of heated basement rocks. In such a case, the
assumption is legitimate that the section's heating in individ-
ual areas of the region (steps or fault-blocks) correlates with
the elevation of the crystalline basement surface. Wherever
the basement is relatively elevated, the conductive depth heat
transfer into the upper interval of the sediment cover is imple-
mented with much lower dissipation (loss) than in the areas
of a thick stratisphere. This position establishes the correla-
tion between the sections' heating and the substrate topog-
raphy. This correlation depends on variable heat-exchange
conditions in the sedimentary sequence intervals differing in
the thickness and relationship between heat-conducting and
heat-shielding intervals of the sedimentary sequence.
t
A review of the PT-KT in the individual fields at the same
depths shows the following. Temperature in most faulted
crestal areas with mud volcanism, diapirism, etc. is always
10-15°С higher than on the distant flanks and plunges (in
the fields of the Lower Kura depression, Kobystan, Baku
Archipelago, Apsheron Peninsula, Balkhan zone, etc.).
The effect of geologic medium's anisotropy resulting in lat-
eral conductive temperature increase over the region's struc-
tural crests, usually by
-5°С depending on variations of
rock density and other thermophysical properties as a func-
tion of dip angles, was figured-in. Thus, each field displays in
the map view a local temperature maximum (a positive geo-
thermal anomaly). Such temperature distribution over the
area of local structures is caused by a substantial effect on
the PT-KT geothermal field (together with regional conduc-
tive heat transfer) by the subvertical convective component
of the total heat flow (heat transfer by the well-heated depth
alkaline ground water). Our estimate of the convective frac-
tion in the total heat flow in the South Caspian Basin fields
is 7-18%.
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