Sedimentary Environment, Diagenesis, and Reservoir Quality of Sarvak Formation (Upper Part) in Siri (E) Oilfields

The Sarvak formation (Late-Albian-middle Turonian) is one of the main oil and gas reservoir units in the southern and southwest of Iran after Asmari formation (Oligo-Miocene). It hosts an important amount of hydrocarbon reserves in this region. Detailed thin section studies of this formation in the Siri field led to the identification of 9 major microfacies, which are deposited in four facies belts (basin, outer-ramp, mid ramp, and inner ramp) in a homoclinal ramp-type platform. Main diagenetic processes affecTed carbonate of this formation are neomorphism, bioturbation, micritization, dolomitization, extensive dissolution, cementation, stylolitization, and fracturing. Diagenetic processes at the upper part of the Sarvak formation and the relative timing indicate that these processes occur in three main diagenetic environments, including marine, meteoric, and burial. The correlation between the porosity and permeability values of core data shows that the reservoir quality is affected by sedimentary environment, sedimentary facies, and subsequent diagenetic processes. Thus the rudists facies (grainstone, rudstone, and floatstone) have a maximum porosity and permeability.