Analysis of Microfacies, Sedimentary Conditions and Diagenetic processes of the Asmari Reservoir in Qaleh Nar Field

The Olig-Miocene Asmari Formation is one of the most important reservoir rocks in Zagros basin and composed of carboantes rocks and locally sandstone and evaporates in southwest Iran. In this research, microfacies, depositonal environemt and diagenetic processes of this formation in a well in Qaleh Nar field have been investigated. Thin section studies indicates that this formation mainly consist of dolomite and limestone. Based on petrographic analysis 3 facies association have been identied in the studied interval namely A, B and C which includes 10 microfacies. The microfacies are attributed to tidal flat (upper intertidal and intertidal), lagoon and shoal. The lack of great barrier reefal microfacies, abundant oolithic microfacies and wide distribution of tidal flat indictes that the Asmari Formation was deposited in a carbonate homoclinal ramp. Sedimentological studies indicate that different diagenetic processes have been affected on the studied interval including cementation, anhyiritzaiton, neomorphism, micritization, bioturbation, dissolution, compaction and dolomitization. These processed have been occurred in three diagenetic environments including marine, meteoric and burial. Among all, dolomtiztion, dissolution and fractureing have positive effects on porosity and enchance reservoir quality, with cementation and anhyritzation have negative effect on it.