Study of pore system in relation to reservoir characteristics of the upper Dalan and Kangan formations in Lavan field, south east of the Persian Gulf

Carbonate Dalan and Kangan formations with the late Permian-early Triassic age are considered as the main gas reservoir rocks in some fields of the Persian Gulf. Carbonate facies of these formations which are related to shoal, lagoon and tidal flats have been developed in a carbonate ramp environment under the arid climate condition. Pores system of the formations under the effect of the primary depositional texture and diagenesis, has a significant control on the reservoir properties. In this study, in order to investigate the effects of these agents on the reservoir quality, hydraulic flow units were described. Then, based on the relationship between the identified hydraulic flow units and depositional and diagenetic characteristics, pores system of the reservoir facies was classified into four classes of porosity-permeability values of high, low, intermediate and high porosity-low permeability. The results show that the diagenetic processes such as dissolution, cementation, dolomitization and to some extent fracture, on the basis of the primary depositional texture, have the important effect on pore system distribution within the reservoir facies, and their reservoir properties. As, pervasive cementation by anhydrite and calcite have been associated with a severe decrease in reservoir quality of grain supported facies. In contrast, dissolution with creation of moldic and vuggy porosity has been acted in a way to change, improve or increase the reservoir quality. Also, in some parts of the reservoir, dolomitization by creation of intercrystalline porosity, and fracture especially in mudstone facies have been improved the reservoir quality.