مینا سادات هاشمی

In the study of the Dariyan Formation (Shoaiba Fm.) in one of the southeastern fields of the Persian Gulf, the sedimentary environment and biostratigraphy of these deposits were investigated on the cores which obtained from this formation. In the studies of the sedimentary environment, seven carbonate microfacies and one mixed carbonate-clastic microfacies were identified, which represent the deposition of the Dariyan Formation in four facies belts, including the inner ramp, middle ramp, outer ramp and deep basin. Also, uniform facies changes, the absence of rudists forming large reefs and the replacement of Lithocodium algae with them indicate the homoclinal carbonate ramp environment.
In biostratigraphic studies based on foraminifera and calcareous algae, five biozones were identified, which represent the Aptian age for this formation. By combining the geological studies, the results obtained from the routine analysis of the cores and the evaluation of petrophysical logs, the reservoir quality of this formation was also studied, which indicated the good reservoir quality in parts of these deposits and especially the layers bearing Lithocodium algae. Based on these studies, the Dariyan Formation is one of the important reservoir formations in the east 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.