ƶƘƫŚƐƯ ƾſŚƴƃ Ĭƴſ - ƂŴŝ ƽŶǀƬƧ ƽŚƷ ƶƿLJ ƾſŚƴƃ ƶƴǀģ æ

ƶƘƫŚƐƯ ƾſŚƴƃ Ĭƴſ - ƂŴŝ ƽŶǀƬƧ ƽŚƷ ƶƿLJ ƾſŚƴƃ ƶƴǀģ æ

________________________________________________________
(
)
*
-
-
.
.
.
)
(
.
A
B
D C
E
.
.
F E D C B A
.
.
.
Chilostomellids
.
F
.
EDS
.
.
Petrography - Stratigraphy Study of the Key Beds in Member 1 of the
Gachsaran Formation (Cap Rock), Agha Jari Oilfield
Abstract
The Member 1 of the Gachsaran Formation is considered as the Cap Rock in petroleum domain of
south of Iran. The cap rock has consisted of a series of Key Beds, which their identification is
necessary to casing point and reducing drilling risk (with regards of pressure change from high to
low in member 1). In Agha Jari oilfield, the cap rock is divided into 6 key beds which can be
correlated through the field. These are A, B, C, D, E and F, respectively from top to bottom. The
key bed A underlies the main salt of Gachsaran Formation (member 2) and is mainly composed of
anhydrite. The key bed B with the lithology of bituminous shale is the most important ones in the
cap rock. The key beds C & D are calcareous and called Chilostomellids bearing layers. The key
bed E is poor in fossil content. The bottommost key bed is F and is consisted of mudstone and
wackstone. These key beds are evaluated with Gamma Ray and Sonic well logs. Chemical analysis
2027
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of selected samples carried out with SEM-EDS analyzer. These data as well as petrography of key
beds indicate that depositional environment is platform edge/Sabkha which periodically charged by
sea water. The result is also verified by Carbon and Sulfur isotopic data of the selected samples
from carbonate and anhydrite layers.
-
(Key Beds)
.
.(
)
Slinger, 1948 & Child,1944; Watson, 1960)
.(Stone & Watson, 1962 1949
-
.
.
°
°
'
(SEM-EDS)
.
.
Humble
.
F
.
E D C B A
.
-A
.
.
Lath
2028
- -
________________________________________________________
.
CarbE CarbD2 CarbD
(
)
.
.
.
.
B
(Main Salt)
-B
- -
.
.(
)
.
.
A
CarbD2
CarbD
.
-C
(Upper Cap
- -
Upper Chilostomellid Limestone
Rock Limestone)
.
.
.
Dunham (1962)
Lamelibranch
Gastropod Chilostomellid
.
-D
- .
(Lower Cap
Lower Chilostomellid Limestone
.
.
C
-E
.
.(Slinger, 1948)
Chilostomellid
.
2029
Rock Limestone)
- -
________________________________________________________
-F
- -
.
.
(Folk, 1962)
(Polymorphinid)
Chilostomellid
.
.
(SEM-EDS)
.
.
A
F
E D
.
( / - ) ‰ 34S
(- / ) ‰ 13C
.
.
.
(EDS)
-
:
.
D
.
Lath
( C)
13
.
2030
.
________________________________________________________
( 34S)
.
-
.
:
.
.
.
-
-
-Child, J. G., 1944, Lower Fars keybeds in the Gachsaran area, Report No. G-647.
-Dunham, R. J., 1962, Classification of carbonate rocks according to depositional texture. In: Ham,
W. E. (ed.), Classification of carbonate rocks: American Association of Petroleum Geologists
Memoir, p. 108-121.
-Folk, R.L., 1962, Spectral subdivision of limestone types, in Ham, W.E., ed., Classification of
Carbonate Rocks, American Association of Petroleum Geologists Memoir 1, p. 62-84.
-Slinger, F. C. P., 1948, Agha Jari lower fars keybeds, Report No. G-721.
-Slinger, F. C. P., 1949, The Agha Jari cap rock, Report No. G-751.
-Stone, A.J., Watson, S. E., 1962, Agha Jari lower Fars keybeds correlation, Report No. G- 1014.
-Strong, M. W., 1939, Notes on petrography and correlation of the lower fars chemical series of
Iran, Report No. G-626.
-Watson, S. E., 1960, Rivision of the lower Fars key beds in Gachsaran field, Report No. G-946.
2031