Microfacies, depositional environment and sequence stratigraphy of the carbonate-evaporate successions of the Kangan Formation in the central part of the Persian Gulf

The Persian Gulf possesses the largest gas fields in the world. The reservoir part of these fields includes upper Dalan and Kangan formations dating back to the Permo–Triassic age, equivalent to Arab countries' Khuff Formation in the south of the Persian Gulf. The present study was based on the core and petro-physical information, including gamma, sonic, and neutron log, in well A in the central part of the Persian Gulf with a thickness of 174 meters. Findings obtained from examining 628 thin sections indicated 12 microfacies in five groups of microfacies (sedimentary environment). These five facies belts consisted of supratidal, intertidal, lagoon, shoal, and open marine (middle and outer ramp). The sum of these facies and their sequence indicated the formation of carbonate-evaporative successions of Kangan in a ramp environment with a gentle slope deposited in the hot and dry climate of the former Triassic. Regarding the combination of microfacies studies and petrophysical logs, two third-order depositional sequences named DS1 and DS2 were identified. Investigations indicated that the Kangan Formation could be divided into four reservoir zones. Zones 1 and 3 with evaporitic or mudstone facies and very low porosity were considered impermeable and non-production capacity parts of the reservoir. These zones were in correspondence to the supratidal microfacies and lagoon. On the other hand, zones 2 and 4 included ooid-bearing grain-supported microfacies with very high porosity. These zones were regarded as the permeable and production capacity parts of this formation and corresponded to the microfacies group of the back shoal.