Geology Reference
In-Depth Information
stratigraphic horizon, as well as in the environment when these horizons
have been subsequently buried under the overlying sediments up to the
present time.
The following assumption was made in the first case for temperature
evaluation during the Mesozoic and Paleocene-Miocene depositional cycle
(this assumption was based on the continuous subsidence of the basin).
The temperatures and the corresponding temperature gradients could not
have significantly exceeded those measured at the same depth in wells that
penetrate these complexes in their current position. The rocks intersected
by the wells almost entirely belong to these complexes.
The correlation for the area of the SE plunge of the Caucasus Major
Meganticlinorium was used as a calibrating function
t
=f(
H
) for the
Mesozoic complex. This correlation integrates the actual measurements
in wells at the Kesh, Begimdag-Temchay, Sitalchay, Shurah-Abad and
Gyadysu. The penetrated thickness of Mesozoic deposits in some of these
wells is 5.5 km (Shurah-Abad). For the Paleogene-Miocene complex, a
similar correlation was used based on wells from the Adzhiveli, Nardan-
Suleiman, Umbaki and Kelany, where the thickness reaches 5.52 km.
The composition of Mesozoic and Paleogene-Miocene rocks and their
thermophysical properties do not change significantly over the entire
South-Caspian Basin. Thus, we use the derived
t
=f(
H
) correlations as a
reference for other regions of basin.
In the second case, the temperature evaluation of Mesozoic complex
during Paleogene-Miocene time and of the Paleogene-Miocene complex
during Pliocene-Quaternary time was conducted as follows. The reference
curve for the Mesozoic complex was taken as a basis and was sequentially
built-up down the entire Mesozoic thickness. The temperature increments
Δ
t
(derived from the temperature gradient) were added to the temperature
value at the maximum subsidence depth of the Mesozoic complex.
The temperature values so estimated took into account the progressing
with time effect of blocking the heat flow from the Mesozoic deposits by the
Paleogene-Miocene clayey sequence. The derived
t=f(H)
function enables
one to estimate the temperature at any present-day depth within the com-
pensated Paleogene-Miocene cycle of subsidence of Mesozoic complex.
The same technique was utilized for determination of temperature of
the Paleogene-Miocene complex at the Pliocene-Quaternary stage of the
region's evolution. The present-day temperature at the base of PS/RBS was
taken for the origin. They were sequentially built-up with the Δ
t
's corre-
sponding to the temperature gradient values from the Paleogene-Miocene
reference curve. We took into consideration the effect of increased heat
transfer by the sandy Pliocene-Quaternary overlying section.
