Geology Reference
In-Depth Information
Figure 7.8 is a generalized representation of the actual data for the South
Caspian Depression. It includes:
t
Correlations of average geothermal gradients (Г, °С/100 m)
in the depth interval 500-2,000 m (zone of maximum oil
and gas reserves in the individual fields and prospects).
t
Local structures' per-unit faulting factor
d
i
and local struc-
tures' folding intensity
К
int
,
t
Formation pressure abnormality factors
К
abn.
(hey may be
considered as diagnostic attributes of the realized heat-mass
transfer model and objective attributes of the dynamics and
intensity of the water-exchange controlling the geothermal
regime on individual structures.)
Figure 7.8 enables the identification in all depression areas of a clearly
inverse correlation of average gradients vs. faulting extent of local highs.
This supports the functional association between phenomenon of forma-
tion temperature leveling and gradient decrease in their sections vs. the
intensity of vertical interformational (inter-bed) water-exchange progress-
ing with the increase in faulting of natural reservoirs.
The legitimacy of this conclusion finds factual support also in the cor-
relation (Figure 7.8) of the geothermal gradients vs. formation pressure
abnormality factor. The Figure shows that on the structures with minimal
К
abn
values (i.e., the conditions of relatively unrestricted water-exchange)
the gradients are low (they correspond with the environment of leveling
the formation temperatures in the process of interformational fluid cross-
flows (thermally-open structures). Contrary to this, on the structures with
obstructed vertical hydrodynamical communicability, the gradients are
maximal. This corresponds with substantial difference in formation tem-
peratures in the hydraulically isolated lower and upper section intervals
(thermally closed structures).
Thus, the quoted materials indicate a definite association between the
prospects' geothermal regime and the mobility of thermal ground waters
(major agent of convective heat-transfer) in their sections.
The hydrogeology and ground water chemistry in the South Caspian
Depression include inverted hydrochemical profile in the post-Lower
Pliocene deposits. It is expressed as sequential replacement down the
sections of individual fields of syngenetic chlorine-calcium brines by
the foreign (invaded through the faults) low-salinity hydrocarbonate-
sodium waters. It enables the clear identification of water type transition
zone and the measure and height of the injection of the foreign alkaline
