Assessment of linking diagenesis history to sequence stratigraphy evidences (systems tract), (a case study: Sarvak Formation in one of the super oil fields, SW, IRAN)

The Sarvak Formation (Late Albian-Middle Turonian) is the most important carbonate reservoir in interior Fars in southwest Iran. The carbonate rocks of this formation have different and complex reservoir properties due to their tolerance to different diagenetic conditions and sedimentary environments. This formation in the Sarvestan oil field mainly consists of white to cream limestone with thin interbedded cream-colored argillaceous limestone and shale. This study aims to identify facies, interpret the sedimentary environment, and identify diagenetic processes and their effect on the quality of the Sarvak reservoir in the Sarvestan oil field. Four wells from the Sarvestan oil field were scrutinized to study petrography and sedimentary environment and to explore the equivalence of diagenetic processes of Sarvak formation from the Upper Cretaceous-aged (Bangestan Group) with the system tracts in the framework of sequence stratigraphy architecture. Based on the study, over 600 thin sections provided from cutting and cores, 14 carbonate microfacies were recognized to be deposited in 4 facies belt zone tidal flat, lagoon, shoal/bar, and open marine in a homoclinal carbonate ramp. Eight types of hybrid porosity derived from deposition, diagenetic and tectonic processes were determined by the petrographic investigations. Six depositional sequences were recognized according to lithological variation, log gamma changes, and vertical changes of microfacies. Facies' associations strongly control the reservoir quality and dissolution near sequence boundaries (Cenomanian-Turonian and Middle Turonian). Some diagenetic features such as karstification, dissolution, cementation, and dolomitization are controlled by relative sea level change, especially in Lowstand Systems Tract (LST). Shoal/bar reservoirs near sequence boundaries at the top of HST have higher porosity than those in other facies belts and sequence positions. In general, in the TST and HST systems tract, the primary marine diagenetic processes, such as micritization and cementation, expands. In the LST systems tract and sequence boundaries, the meteoric diagenetic processes, such as dissolution, develop. The best reservoir quality occurs in the upper parts of the highstand systems tracts, which contain primary grain-supported intervals or dissolution porosity. The studies show that reservoir potential is controlled in a sequence stratigraphy framework (A combination of depositional environment and diagenesis) in the carbonate sequence of the Sarvak Formation in sequence stratigraphy framework.