Geology Reference
In-Depth Information
Certain patterns are established in the spatial AHFP distribution in the
reservoirs:
t
Continuous increase in excess formation pressure over the
hydrostatic and in the abnormality factor in the direction
from the platform flank of the trough toward the geosyncli-
nal flank (west to east) and down the stratigraphic section
(from the average of 1.21 in the Asmari Formation to 1.45 in
the Arab formation) (Table 3.8, Figure 3.12).
t
Increase of the said parameters with increasing thickness of
Fars and Hith seals, with the depth of productive reservoirs
and decrease in degree of fracturing.
t
The occurrence of maximum abnormality factor values in
the fields located relatively close to the neotectonically active
Zagros Mountains (the depth to the Asmari reservoir of over
1,000 m).
The first feature clearly correlates with the known data of hydrody-
namic communication in most fields between the Asmari and Bangestan
reservoirs. This resulted in the formation of common oil-water contacts
(Aliyev and Zabanbark, 1974; Levorsen, 1970; Hall and Warman, 1973)
and in genetic similarity of the hydrocarbons
in
all stratigraphic intervals
(Dunnington, 1961; Hunt, 1982).
It may be considered as an objective confirmation of the commonal-
ity in the region of vertical inter-formational fluid-mass-transfer from the
lower into the upper stages of the sediment cover.
The second feature is an illustration of formation pressure abnormality
values in the reservoirs controlled by the extent of the discharge. In the
most contrasting form, it shows up in comparing the abnormality factor
values in the Karanj, Marun and Ahwaz fields with the same parameters in
the Masjid-e-Suleiman, Haft-Kel and Gachsaran fields.
The former group is deeply buried (respectively, 2,100; 2,320 and 2,560
m to the top of Asmari), has a thick seal and the abnormality factors of
1.42; 1.32 and 1.35 (see Figure 3.12).
The latter group includes eroded, maximally close to the surface fields
Masjid-e-Suleiman, Haft-Kel and Gachsaran (respective depths to the
top of Asmari: 180 m with the abnormality factor 1.04; 600 m with the
abnormality factor of 1.06; and 750 m with the abnormality factor of 1.08).
In these fields the waterhead system drainage (which caused numerous
