Facies distribution, sequence stratigraphy, and reservoir quality of the Oligo-Miocene carbonate sequences (Asmari formation) in the Dezful embayment, SW Iran

The Asmari succession is among the greatest productive hydrocarbon-bearing rock units in the Middle East. This paper examines the biostratigraphy, sedimentary environment, and depositional sequence of the Asmari reservoir in the Haft-Kel Field. This succession in the Haft-Kel Field contains limestones, dolostones, anhydrites, and argillaceous limestones and is bounded between the Pabdeh and Gachsaran formations. Paleontological research has led to the creation of three assemblage zones in this region. These zones present an age range from the late Oligocene (Chattian) to the early Miocene (Aquitanian). Also, detailed petrographic examinations and facies analysis led to the recognition of 14 types of microfacies, ranging from open marine environments to intertidal and supratidal systems. The distribution and association of recognized microfacies proposed carbonate ramp-type platform deposition for the Asmari Formation. In addition, three third-order depositional sequences (sequences 1, 2, and 3) have been recognized through the Asmari Formation in the Haft-Kel Oil field that is well correlated with sequences IV, V, and VI proposed by van Buchem et al. (2010), respectively. Using the Hydraulic Flow Unit (HFU) concept, six rock types have been identified for the Asmari reservoir. Finally, three reservoir zones, comprising none, moderate, and good reservoir zones, were introduced for the Asmari reservoir in Haft-Kel Field. No reservoir zones are visited in the lower part of the formation in depositional sequence 1 and to some extent in the Low Stand Systems Tract (LST) part of depositional sequence 2 and 3, while moderate to good reservoir zones are developed in the upper intervals of the formation, especially in the High Stand Systems Tract (HST) parts of depositional sequence 2 and 3.