Page 300 - Petroleum Geology

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STRATIGRAPHY - EAST SIRTE BASIN

WEST CENTRAL
COMPARISON Of
NOMENCLlTURE USE0 BY
TERRY a WILLIAMS 1969 ELGlZI MEMBER
(LIMESTONES) Y
8 PRESENT PAPER
Y
GIR
TERRY 8 WILLIAMS PRESENT PAPER
(LIMESTONES - DOLOMhTES - INHIDrllTESJ
UPPER KHEIR
XHEIR
LOWER KHLIR
ZELTEN UPPER SABlL
IDRlS INTISAR
LOWER ZELTEN UPPER SABlL
CARBONATE PLATFORM
HElRA SHALE SHETERAT
(LIMESTONES / DOLOMITES )
HEIRA LI I LOWER SABlL
DOLOMiTE

. . .
Fig. 12-12. Stratigraphy of the east Sirte basin. Dotted lines are facies variations: heavy
lines are generalized time lines. (Reproduced from Brady et al., 1980, p. 547, fig. 4, with
permission. )

The Intisar “D” reef (Brady et al., 1980) is of similar size at similar depth,
roughly circular in plan with a diameter of about 5 km, and a thickness of
385 m. It differs from the other reefs in the area in that it has a lithologically
homogeneous reservoir. However, its permeability varies greatly, from 4 to
over 500 md, with an average of at least 200 md indicated by well perform-
ances (compared to 87 md arithmetic average of measured horizontal perme-
ablities). Porosities range from 4 to 35%, with a field average of 22%.
The “D” reef is full to spill point with 40”API” undersaturated paraffinic
crude, which is rather heavier than the oil in reefs to the north-west, and
lighter than that in “E” to the south-west. The oil/water contact is at 2880
m (9450 ft) below sea level, giving a maximum oil column of 291 m (995 ft).
Original oil in place is estimated to be 1.8 X lo9 bbl (286 X lo6 m3), and the
recovery factor may be as high as 75-80% with secondary recovery program-
mes.

* There is usually some variation in reported gravities: the gravities of individual wells and
production zones may differ from each other and from the field average of produced crude
oil.