FACIES ANALYSIS AND DEPOSITIONAL SEQUENCES OF THE UPPER JURASSIC MOZDURAN FORMATION, A CARBONATE RESERVOIR  IN  THE KOPET DAGH BASIN, NE IRAN

M. A. Kavoosi*+,  Y. Lasemi**, S. Sherkati* and R. Moussavi-Harami***

* National Iran Oil Company Exploration Directorate, 1st Deadend, Seoul Street, NE Sheikh Bahaei Square, PO Box 19395-6669, Tehran, Iran.

** Department of Geology, Teachers Training University, No.49, Mofateh Ave, Tehran 15614, Iran.

*** Department of Geology, Ferdowsi University, Mashhad, Iran.

+ Corresponding author. m.kavoosi@niocexp.ir

Upper Jurassic carbonates of the Mozduran Formation constitute the principal reservoir intervals at the giant Khangiran and Gonbadli gasfields in the Kopet Dagh Basin, NE Iran. These carbonates were investigated using detailed field studies and petrographic and wireline log analyses in order to clarify their depositional facies and sequence stratigraphy. Facies were interpreted to reflect deep basin, fore-shoal, shelf margin, lagoon, tidal flat and coastal plain depositional systems.

The Mozduran Formation is composed of six depositional sequences. Thickness variations were controlled by differential subsidence. Aggradation on the platform margin and reduced carbonate production in the deep basin together with differential subsidence resulted in the creation of a narrow seaway during the late Oxfordian. Petrographic studies suggest that Mozduran Formation carbonates had a low-Mg calcite mineralogy during the Oxfordian, and an aragonite to high-Mg calcite mineralogy during the Kimmeridgian. Reservoir pay zones are located in highstand systems tracts within the lower and middle Kimmeridgian depositional sequences. The rapid lateral thickness variations of these sequences were controlled by tectonic factors, leading to compartmentalization of the Mozduran Formation reservoir with the possible creation of stratigraphic traps, especially at the Khangiran field.

Key words:  Kopet Dagh Basin, Upper Jurassic, Mozduran Formation, facies analysis, sequence stratigraphy, reservoir, Iran, carbonates.

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