Geology Reference
In-Depth Information
There is some correlation between water type and salinity: a depressed
salinity (32-135 mg-equiv. or 9.2-38.6 g/l) is observed in the alkaline
waters and elevated salinity (60-240 mg-equiv. or 17.2-68.5 g/l) in the hard
waters. The chlorine content is 10-130 mg-equiv.; the sulphate-ion content
does not exceed 2 mg-equiv.; total alkalinity is 1-9 mg-equiv.; the concen-
tration of water-soluble organic acid salts is up to 8 mg-equiv.; sodium and
potassium concentrations range 14 to 115 mg-equiv. The primary alkalin-
ity factor is 0.1-45%-equiv., the secondary salinity factor, 0.1-20%-equiv.
(see Tables 2.1, 2.4).
On the local structures, the lowermost salinity waters are associated
with the crestal areas. In the subsided areas, both water salinity and hard-
ness increase.
The correlation is recorded in all studied Apsheron Peninsula and
Southwestern Kobystan areas between the water salinity, extent of the ero-
sion and faulting extent of the Diatomaceous Fm. rocks. This correlation
is omnipresent and is observed both for the hard and alkaline waters. For
example, at the Arzani-Klych prospect in the Southwestern Kobystan, the
Diatomaceous Fm. is eroded and somewhat faulted. The water salinity is
82.6-121.2 mg-equiv. At the same time at the adjacent Ragim prospect, the
rock exposure on the surface and faulting are significant; maximum water
salinity there is 40.8 mg-equiv. A similar phenomenon is observed on the
Apsheron Peninsula. At the Khorasany prospect there, the Diatomaceous
rocks are not exposed on the surface and the ground water salinity is 90.0-
135.6 mg-equiv. In addition, at the Djorat Prospect, this interval is partially
eroded and much stronger faulted; the salinity there does not exceed 8.2
mg-equiv.
The actual areal water distribution in the Diatomaceous Fm. indicates
a clear trend to increased salinity from the exposed, eroded and much
faulted structures to less exposed and more tectonically quiescent highs of
the Apsheron Peninsula. Ground water hardness also increases in the same
direction (Figure 2.3).
Ground waters of all stratigraphic intervals in the Paleogene-Miocene
complex are relatively similar within the framework of each major water
type, hard and alkaline (see Table 2.4), which suggests that a commonality
of causes led to this similarity within each interval. It is noteworthy that
in all intervals of the section the salinity of alkaline and sulphate-sodium
waters usually does not exceed 70.0 mg-equiv. whereas it is mostly higher
for hard waters.
Field data also indicate a clear salinity growth up the section. It par-
allels the general reservoir property deterioration in the same direction
(Table 2.5). This trend is obvious both in the hard and in the alkaline
