Relationship between sedimentary sequences and diagenetic processes with the reservoir zones of the Asmari Formation in one of the oil fields in the southwest of Iran

The Oligo-Miocene Asmari Formation is one of the most important hydrocarbon reservoirs in the Zagros sedimentary basin, especially in the Dezful depression. The Formation in most of the oil fields of the Dezful depression consists of a mixed carbonate-siliciclastic sequence. In this study, the relationship between sedimentary sequences and diagenetic processes with reservoir zones is considered. For this purpose, sedimentological data and petrophysical logs of a key well were used. Based on microscopic studies on the core thin sections, four detrital petrofacies and eight carbonate microfacies were identified that were deposited in four facies belts, including open marine, shoal, lagoon, and tidal flat environments, related to a homoclinal ramp. In addition, six depositional sequences (third order) were identified by facies analysis and well logs. Reservoir properties have been increased by dissolution and dolomitization with pore space expansion, while being decreased by cementation and compaction. The Asmari Formation in the investigated well is subdivided into eight reservoir zones based on sedimentary characteristics and petrophysical properties. The coincidence of the facies boundaries with the reservoir zone boundaries in most cases shows that the changes in the reservoir properties are mainly related to the changes in the sea level. This is well-known in the lower zones