Investigating the effects of sedimentary environment and diagenetic processes on the quality of Sarvak reservoir formation within a sequence stratigraphic framework, Kupal Oil Field

The Sarvak Formation deposited in the North to Northeastern margin of the Arabian Platform during the Mid-Cretaceous (Albian-Turonian), and is extensively encountered in the Folded Zagros of southwestern Iran. It is the most important reservoir unit after Asmari Formation in Iran. Petrography of microscopic thin sections in studied wells led to determination of nine microfacies that deposited in 3 sub-environments; restricted lagoon, lagoon-open marine and shoal in an interior part of carbonate ramp. Petrographic studies revealed that since deposition, the Sarvak Formation experienced several diagenetic realms including marine, meteoric, burial and telogenetic diagenetic environments. Location of the studied wells shows that the relative depth of the Sarvak Formation ramp decreases from the east to the west. Also, the results show that the Sarvak reservoir quality affected by various diagenetic processes such as micritization, dissolution, dolomitization, cementation, stilolitization and fracturing. These diagenetic successions are mainly restricted to the upper and lower parts of the Cenomanian-Turonian disconformity. Meteoric water infiltration below this disconform boundary and related karstification led to development of moldic and vuggy porosity a long with reservoir quality increase. Based on the sequence stratigraphic study, three third-order sequences were recognized in the middle Cenomanian to middle Turonian part of the formation. The results of this research show that the reservoir quality distribution in this unit is primarily controlled by depositional facies so that the rudist microfacies (grainstone, floatstones and rudstones) have the best primary reservoir qualities though, it has also been drastically improved by dissolution in paleoexposure surface