Description and correlation of facies and depositional sequences of Kangan and Dalan formations in Permian-Triassic carbonate ramp, central and eastern Persian Gulf

The upper Permian–Lower Triassic Dalan and Kangan formations comprise two of the most important hydrocarbon reservoirs in the Persian Gulf. The goal of this study is to analyze sedimentary microfacies and establishing a conceptual depositional model and the sequence stratigraphy framework of the upper Dalan and the Kangan formations in central and eastern oil fields Persian Gulf. According to petrographical studies carried out on 3651 thin sections, fifteen carbonate microfacies associated with tidal flat, lagoon, shoals and open marine depositional settings were identified. Microfacies analysis and their vertical and lateral changes, gamma-ray response as well as comparison with the ancient and modern analogues suggest a gentle carbonate ramp as the depositional model for the studied successions. Comparison of the microfacies abundances in the studied oil fields revealed dominance of the shallower depositional setting in the central field studied well compared to those of the eastern oil fields which indicates a northeast-ward deepening paleo-dip of the sedimentary basin. Five third-order depositional sequences were established; three sequences labeled here as USD1, USD2 and USD3 in the upper Dalan Formation and two sequences in the Kangan Formation namely KGS1 and KSG2. The sequences comprise TST and HST system tracts, separated by sequence boundaries and maximum flooding surfaces. While the sequence boundaries were identified based on the sedimentary successions or microfacies indicative of relative sea level fall, the maximum flooding surfaces were recognized based on occurrence of deepest microfacies in the sequences. Correlation of the established sequences in the studied wells represents an overall shallowing upward depositional pattern.