Geology Reference
In-Depth Information
mostly by the thermal effect of radioactive decay in the Earth crust, forms
to a substantial degree due to convective component. The integral effect of
both components is manifested by a dual correlation of average geother-
mal gradients. The first is geothermal gradients vs. depth to base of the
Productive (Red-Bed) Sequence (
Н
base PT
, Н
п KT
) [(
Н
base PT
, Н
base KT
)] (conduc-
tive component prevailing). The second is geothermal gradients vs. depth
to the top of the transition zone of syngenetic chlorine-calcium waters into
hydrocarbonate-sodium waters genetically foreign to the enclosing sedi-
ments (
Н
tran.zone
) (convective component shows up)
2
.
Of a significant interest in this connection is determining the role and
place of each of the stated factors in the formation of geothermal fields
in oil and gas accumulations. Also important is the determination, albeit
in the first approximation, of spatial (depth) position of the zones and
therefore of the boundary between them, where the convective compo-
nent of the total heat flow acquires noticeable role. On the other hand,
as the agents conveying heat into the Productive (Red-Bed) sequence
from the underlying complexes are low-salinity alkaline waters, the lower
boundary of a clear manifestation of the convective heat transfer may
be interpreted to be the initial segment of intense generation and broad
development of hydrocarbonate-sodium waters and their transit into the
overlying sediments.
Based on the data from fields in the Apsheron Peninsula, Lower Kura
depression and Apsheron-Balkhan zone of highs, are shown the corre-
lations Г
=
f
(
Н
base PT
,
Н
base KT
)
and Г
=
f
(
Н
tran.zone
) approximated by expo-
nential curves Г
=
а
Н
в
(Table 4.1). (Obviously, these correlations should
be viewed mostly qualitatively as it is a practical impossibility to assert
for each correlation the connection of variables only between them-
selves without a superposing effect of other additional geologic factors).
Table 4.1 show that the values of their angle factors are different: different
2
The differentiation of total heat flow into the stated components according to
the mentioned attributes is to a certain extent tentative. The reason is that both
components indirectly participate in average geothermal gradients. However,
under specific conditions of the region there are cases where at the same depth to
the complex's base average gradients are substantially different (which is caused
by different depths to the water type transition boundary). And the other way
around: at equal section's saturation with alkaline waters the gradient variations
are determined by the depth to the base of the Middle Pliocene. Then the indicated
correlations objectively describe qualitative relationships between both compo-
nents of the total heat flow within local structures.
