Role of the depositional environment and diagenetic effect on reservoir quality of the Upper Surmeh Formation in Salman Field

The Upper Surmeh Formation (Upper Jurassic) consists of limestone, dolomite and interbeded anhydrite equivalent to the Arab Formation in the southern Persian Gulf. This succession is the main producing reservoir of the Jurassic system in the Arabian plate. This research was carried out based on core (thin section, porosity - permeability, capillary pressure data) and well log data to study the depositional environment and diagenetic effects on reservoir quality of the upper part of the Surmeh Formation. Petrographic investigations led to recognized nine microfacies which were classified in four facies belt including supratidal, intertidal, lagoon and shoal which were deposited in an arid homoclinal carbonate ramp. Diagenetic processes affected reservoir quality of identified microfacies. Among them, dolomitization, anhydritization and cementation are the main effective processes. Dolomitization increased reservoir quality but the anhydritization and cementation decreased reservoir quality. It is important to note that relevant reservoir quality is improved by development of shallow marine facies associations and secondary diagenetic events. Based on the porosity, permeability and mercury injection pressure data, anhydrite and anhydrite bearing mudstone have very low reservoir quality whereas ooid and bioclastic pack ston to grainstone have the best reservoir quality.