A REVIEW OF PERMO-TRIASSIC RESERVOIR ROCKS IN THE ZAGROS
AREA, SW IRAN: INFLUENCE
OF THE QATAR-FARS ARCH
B. Esrafili-Dizaji* and H. Rahimpour-Bonab*+
* Department of Geology, College of Science,
University of Tehran, Iran.
+Corresponding author, email: email@example.com;
Four “supergiant” and numerous giant gasfields have been discovered in the Zagros area of SW Iran. The gasfields are concentrated
in the eastern part of the foldbelt, in Fars Province
and the adjacent offshore, and produce from Permo-Triassic
carbonates equivalent to the Khuff Formation. The carbonates belong to the
upper member of the Dalan Formation and the overlying
Kangan Formation. Reservoir rock quality is strongly
influenced by tectonic setting and depositional environment, and also by diagenesis.
The highest quality reservoirs occur in oolitic shoal
facies; fracturing (especially in onshore fields) and dolomitisation
(in offshore fields) have also influenced reservoir quality. Anhydrite plugging
is common in reservoirs in offshore fields, while calcite cementation is dominant
in onshore reservoirs.
Facies variations in the Dalan-Kangan Formations appear to correspond to syndepositional palaeohighs and
depocentres. In the Eastern Zagros (Fars area), thickening of the Dalan Formation corresponds to a Mid-Late Permian depocentre referred to here as the Permian Fars
Basin. As a result of sea
level fall, this depocentre evolved into a hypersaline lagoon with evaporite
deposition (Nar Member). In the Triassic, the depocentre
evolved into a palaeohigh as indicated by thinning
and facies changes in the Kangan Formation.
The results of this study draw attention to variations in
the reservoir quality of the Dalan-Kangan Formations.
Much of this variation was due to the influence of the Qatar-Fars Arch.
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