Microfacies, Sedimentary Environments and Diagenesis of the Dariyan Formation in Southeast of the Persian Gulf

Dariyan Formation (with Aptian age) is considered as one of the important oil reservoir of the Zagros and Persian Gulf sedimentary Basin. This formation in the studied field in southeast of the Persian Gulf, is considered as the most important oil reservoir rock. In this study, microscopic thinsections that prepared from the cores of the Dariyan Formation, were investigated. The study of the microfacies of the Dariyan Formation in this field led to identification of seven carbonate microfacies and one mixed carbonate-clastic microfacies, which were deposited in four facies belt including the inner ramp, middle ramp, outer ramp and deep basin. The investigating of the fauna in the studied microfacies shows a relatively shallow marine environment (in some intervals representing the deep marine environment), generally. Uniform facies changes and the absence of rudists and corals which are reef-building faunas as well as the replacement of Lithocodium algae with less ability to form the large reefs, represent the homoclinal carbonate ramp environment, which contain «patch reefs». Importanat diagenesis processes such as: cementation, bioturbation, pyritization, phosphatization, dolomitization, dissolution, Mechanical and chemical compaction and fracture has affected the carbonate rocks of this Formation. Correspondence of porosity and permeability data of the cores indicates that the reservoir quality of the Dariyan Formation in the studied field was affected by facies, sedimentary environment and diagenesis factors, so the lithocodium- bearing facies (boundstone-flootstone) have the most porous facies.