Determination of the Reservoir Layers of Ilam Formation on the Basis of Facies and Seismic Studies in the Southeastern Persian Gulf

Ilam formation (Santonian-Campanian) is one of the major reservoirs of Bangestan group composed mainly of carbonate rocks. Facieses, depositional environment, and reservoir quality of Ilam formation in one of the oilfields in the southeast of the Persian Gulf were investigated in this study. The facies analysis indicated that the sediments of this formation had precipitated in a homoclinal and shallow carbonate ramp depositional environment. Most of sequences in the wells were studied in the field consisting of open shallow marine and restricted marine facieses. Thin layers of middle and outer ramp facieses of the deeper parts exist in some parts of sequences. Ilam formation based on the characteristics of the reservoir and facies properties can be divided into 7 reservoir layers. The upper layer is formed of rework limestone in an east-west trending channel-like structure. The other layers are A, B, C, D, E, and F; the A reservoir layer with a thickness of 35 m and a porosity of 18% is the most porous layer of Ilam formation; next placed in the order of layers are C, E, layer, channel-like facies, D, B, and F. The F layer with an average porosity of less than 5% and a permeability of less than 0.5 mD does not possess good reservoir quality. The position and orientation of the layers were determined by seismic data in the field of study.