Geology Reference
In-Depth Information
oil cross-flows, hence the role of this process in the formation of accu-
mulations, was much smaller. This determined predominant association of
major oil reserves with alkaline waters.
The examples establish the oil-gas-saturation of the section to be a func-
tion and result of alkaline waters in the section. This feature presents alka-
line waters in the sections of local structures, either singularly or in the
composition of hard formation mixes, as indicators of probable hydrocar-
bon saturation.
In our belief, it is legitimate to use the reviewed factors as qualita-
tive (indirect) indications of hydrocarbon saturation of the Productive
Sequence sections on local structures.
In order to come up with clearer (quantitative) hydrochemical attributes
for the forecast of hydrocarbon aggregations, taking into account the type
of suggested accumulations, distinctive attributes of the waters in oil, gas
(gas-condensate) accumulations and unproductive intervals should be first
identified.
A comparison of the formation waters' chemical composition in the
Productive Sequence oil and gas-condensate accumulations of the region
was performed (Mekhtiyev, Rachinsky and Palaudin, 1970). The study found
that GWC aquifer waters in gas-condensate accumulations, compared with
waters of equivalent horizons in the adjacent fields containing oil accumula-
tions, are usually of higher salinity and lower alkalinity (or higher secondary
salinity factors in the hard water medium) (Tables 10.2-10.4). For instance,
total salinity in the near-GWC aquifer waters of gas-condensate accumula-
tions in the KS and PK Formations (Zyrya field in the Apsheron oil and gas
area, Table 10.2) is, respectively, 91.6 and 58.6 mg-equiv. and primary alka-
linity factors are 5-12 and 16-24.6%-equiv. In the adjacent Kala Field the
KS and PK Formations include oil accumulations; average formation water
salinity there is, respectively, 61.4 and 50.5 mg-equiv. with primary alkalin-
ity factors of 39 and 42%-equiv.
A similar picture appears when comparing the formation waters of gas-
condensate accumulations in the NKP Fm. at Karadag (total salinity 81.8
mg-equiv., primary alkalinity factor 5.1%-equiv.) and of oil accumulations
in the equivalent interval in the adjacent Lokbatan Field. There, the same
attributes are 50.0 mg-equiv. and 36%-equiv. (Table 10.2). In the same area
the formation waters in gas-condensate accumulations of the PK Fm. at
Lokbatan (south flank) have salinity of 48.4 mg-equiv. and a primary alka-
linity factor of 13.2%-equiv., whereas in the nearby Yasama Valley Field
(where the PK Formation is oil-saturated) the water salinity is 63.0 mg-
equiv. with a primary alkalinity factor of 23%-equiv.
