Geology Reference
In-Depth Information
hydrochemical criteria for the stated stratigraphic intervals reviewed below
should be considered as tentative.
The Paleogene-Miocene deposits in the North and SW Kobystan are
generally well exposed. Local structures are significantly faulted. Mud
volcano activity is intense. The existence there of large natural gas aggre-
gations does not appear likely. This, however, does not preclude the pos-
sibility of gas and gas-condensate accumulations wherever the stated rocks
are deeper buried in SE Kobystan and on West Apsheron.
Hydrocarbon accumulations in the Pliocene (Productive Sequence) and
Paleogene-Miocene deposits in general formed through genetically similar
mechanisms. Taking this into account, it is suggested that the favorable
conditions of the gas occurrence were low ground water mobility caused
by the absence of significant foci of protracted fluid discharge and hydro-
carbonate-sodium or sulphate-sodium ground water type in the envi-
ronment of total section's isolation from surface water infiltration. In the
former case, the optimum primary alkalinity factor values are believed to
have been 1 to 7%-equiv. and salinity about 60-70 mg-equiv. In the latter
case, the secondary salinity factor should have been up to 4%-equiv. and
salinity of 70-90 mg-equiv. A higher primary alkalinity factor is typical
of oil-saturated intervals, the chlorine-calcium and chlorine-magnesium
types respectively, of nonproductive and poorly-gas-saturated intervals.
In general, while searching for gas accumulation zones in the Paleogene-
Miocene, special attention should be paid to the identification of regional
areas of alkaline water occurrence as most likely evidences of possible
gas-saturation.
Due to insufficient knowledge, the criteria for the Mesozoic are also ten-
tative. The data quoted in previous chapters show that low-salinity alkaline
waters are common. In addition, they are associated with hydrocarbons.
Despite this, the Mesozoic sediments over the SE plunge of the Caucasus
Major Meganticlinorium, under all other conditions equal, have relatively
lower oil and gas potential than the equivalent intervals in the Apsheron
and Kobystan oil and gas areas as well as in the zones of gravity maxi-
mums in the Lower Kura Depression. This conclusion is substantiated by
active hydrodynamical regime in the former region and by high faulting of
its local structures. Both factors under specific geologic conditions of the
region play a negative role, not facilitating the preservation of accumula-
tions. Contrary to the stated, the Mesozoic in the Apsheron, Kobystan and
Lower Kura Depression are at great depths, less faulted and are under more
favorable hydrogeological environment determined by lower ground water
mobility. These circumstances provide for better preservation of hydrocar-
bon aggregations against degassing and destruction by the flowing waters.
