Microfacies Analysis and Depositional Environment of the Ibrahim, Azkand and Anah Formations in Selected Oil Fields of Northern Iraq.

This study focuses on the analysis of the Ibrahim, Azkand, and Anah formations within three major oil fields (X, Y, and Z) located in the Low Folded Zone of Iraq. Integrated microfacies and stratigraphic interpretations reveal a regressive depositional succession spanning the late Oligocene to early Miocene. The lower and middle intervals of the Ibrahim Formation are characterized by microfacies SMF-3, deposited in the deeper sector of Zone FZ-3, interpreted as a toe-of-slope environment under low-energy, distal slope conditions. The upper part of the Ibrahim Formation is dominated by microfacies SMF-4, reflecting a distinct shallowing into a shallower platform setting within the same zone (FZ-3) and marking the onset of a marine regression. The overlying Azkand Formation records continued platform progradation, with its lower section represented by microfacies SMF-5, indicative of an upper slope environment (Zone FZ-4), and its upper part is defined by microfacies SMF-7, characteristic of a high-energy reefal system (Zone FZ-5). The Anah Formation begins with microfacies SMF-8 in its lower part, deposited in an open marine platform interior (Zone FZ-7), and evolves upward into microfacies SMF-18 in the middle and upper sections, representing a restricted platform interior (Zone FZ-8). Gamma-ray logs, which show a decreasing radioactivity trend and confirm a shallowing-upward trend of the depositional environment, corroborate this regressive succession. The depocenter lies near field Z, while field Y occupies a basinal position. The paleo-shoreline extended northwest–southeast across Iraq, aligned through fields X and Z, delineating a rimmed carbonate platform with implications for reservoir characterization and exploration.