Geology Reference
In-Depth Information
TotalFina-Elf ) drilled a “dry” hole there (TD 6,700 m), anticipating to get
oil reserves on the order of 120 MMT and gas
reserves over 2
TCM
(see
Table 11.2).
The latter case is especially symptomatic geologically. It appears that
the Apsheron prospect has the entire set of the necessary conditions for
the formation of a large hydrocarbon aggregation. It has a clear, con-
trasting, large and relatively weakly faulted brachy-anticlinal high syn-
chronous in its emergence and subsequent evolution with the adjacent
productive structures. It has satisfactory reservoirs. It is relatively close
to the Volga paleo-delta. It has thick clay barriers in the upper section.
The structure is open toward the suggested hydrocarbon generation zone
in the center of the basin. It is positioned between the giant gas-conden-
sate field Shahdeniz and the group of largest oil-gas fields Neftyanyye
Kamni-Gyuneshli-Chirag-Azeri.
Nevertheless, well testing did not discover commercial hydrocarbons
in the penetrated section. A similar geologic situation occurred at the
prospects Umid, Seyyar, Nakhchyvan, Zafar-Mashal, Ogurchin, Fersman,
West-Erdekli and Enzeli-More. A comparison of these unproductive highs
with other oil and gas structures in the region, approximately in the same
geologic position (Bulla-More, Bakhar, Shahdeniz, Chirag, Azeri and oth-
ers), shows a major difference between them. The top of the Productive
Sequence (Red-Bed Sequence) at all these prospects is deeper than 1,800 m
(Nakhchyvan, 2,000 m; Zafar-Mashal, 3,200 m; Seyyar, 2,980 m; Absheron,
2,400 m; Ogurchin, 3,000 m; West-Erdekli, 2,800 m; Fersman, 3,800 m;
and Enzeli-More, 2,400 m). Moreover, on all highs with oil and gas accu-
mulations, it is usually shallower.
The effect of depth to the top of the Productive Sequence (Red-Bed
Sequence) (
Н
(Red-Bed Sequence)
in meters) and of the extent of its erosion
(h
пт
(
Red-Bed Sequence
)
in meters) on oil and gas occurrences was identified.
For this purpose, the correlation of these parameters with the original
in-place hydrocarbon quantities А+В+С
1
(
Q
d
, MMT oil equiv/km
2
) on
individual structures was conducted for all areas of the region. The corre-
lation showed that with the increase in the depth to the top, the reserves
density consistently declines, crosses the commercial efficiency line (for
instance, the Umid top of the Productive Sequence is at 1,700 m, Bulla-
More-2 at 1,750 m and Babek possibly at 1,800 m and reaches zero).
Simultaneously, oil-gas and gas-oil aggregations are replaced by gas and
condensate accumulations. On the other hand, optimizing of the hydro-
carbon accumulation conditions on relatively slightly eroded structures
with relatively shallow Productive Sequence (Red-Bed Sequence) was
conducted for the structures where reserves density in all areas is at its
maximum (Figure 11.1).
