Comparative analysis of Permian–Triassic sequences in the Eastern Persian Gulf: insights into their paleoenvironments and diagenetic history

The Late Permian–Early Triassic Upper Dalan Member and Kangan Formation form one of the richest and most important hydrocarbon reservoirs in the Persian Gulf. To investigate the paleo-depositional environments and sequence stratigraphy of this carbonate-evaporite sequence, two wells (labelled here as A and B) were selected from two oil fields in the eastern part of the Persian Gulf. A total of 15 carbonate microfacies have been identified in a carbonate ramp setting, sloping towards the northeast. The diagenetic history of the succession includes marine, meteoric, and shallow and deep burial diagenesis. Dissolution and dolomitization enhanced the reservoir quality, whereas calcite and anhydrite cementation along with mechanical compaction significantly reduced the reservoir properties. Five third-order depositional sequences were determined using the transgressive-regressive model. Three third-order depositional sequences were identified in the Upper Dalan Member, along with two third-order depositional sequences in the Kangan Formation. An erosional unconformity separates the Upper Dalan Member and Kangan Formation, which coincides with the boundary of the Permian and Triassic strata. This boundary is associated with a major global relative sea-level fall, which has yielded major effects on sediments.