DEPOSITIONAL ENVIRONMENTS, FACIES DISTRIBUTION, AND POROSITY ANALYSIS OF YAMAMA FORMATION IN MAJNOON OILFIELD. SEQUENCE STRATIGRAPHIC APPROACH
Due to the importance of petroleum exploration and production in the oil industry and developments. Therefore, this study targets one of the more important reservoir rocks in Iraq, which it Yamama Formation in the Majnoon oilfield, southern Iraq. The facies distribution showed that the formation was deposited on a ramp platform. Seven main carbonate facies were distinguished in the studied area. Based on these facies, Yamama Formation was represented to deposit on a ramp setting, that consist of different sedimentary environments. The main depositional environments represented by the shoal, middle - outer ramp and deep outer ramp environments. Eventually, the Yamama Formation is divided into two main sequences. The lower part of the formation was a regression phase that deposited highstand system tracts, named Yamama sequence one. The upper was a transgression phase deposited transgressive system tracts named Yamama sequence two. The diagenetic processes showed that the early and late dissolution and cementation are important that affected the reservoir characteristics. Dolomitization is not an active process in the formation. Petrophysical properties represented by primary and as well as secondary porosity were studied and processed to evaluate the reservoir characteristics. The data were obtained from wireline logs and core data from plugs and thin sections. Good reservoir property units were located in a high-energy shoal environment and found in other environments depending on secondary porosity and dissolution processes activity. According to porosity cut-off, the formation was divided into five units that have porosity more than the lower limit of the worthy values.