Evaluation of the Sequence Stratigraphy and Sedimentary Environment of the Asmari Formation in the Southwest of Iran: (Case Study of Gurpi and Asmari Anticlines Masjed Soleiman Oil Field)

The aim of this study is to examine the Asmari Formation from the Oligo-Miocene epoch, an important reservoir formation in Iran. To facilitate a comprehensive comparison of lithological changes and sedimentary environments across a broader spectrum, we analyzed 400 samples taken from a section in the Masjed Soleiman oil field. Additionally, we studied sequence stratigraphic of the Asmari anticline in the Dezful embayment and the Gurpi anticline in the Izeh zone. Petrographic analysis identified 18 sedimentary microfacies deposited on a carbonate platform of a homoclinal ramp. These microfacies were observed solely in the inner ramp environment in the subsurface section (Masjed Soleiman section), in both inner and outer ramp environments in the surface section of the Asmari anticline, and across all three inner, middle, and outer ramp environments in the surface section of the Gurpi anticline. Polarizing and Cathodoluminescence microscopy were utilized to assess diagenetic processes within the Asmari Formation in the surveyed areas. Significantly, diagenetic processes observed in the Asmari Formation limestones encompass micriticization, bioturbation, organism excavation, various types of cementations (marine, meteoric, and burial), dissolution (meteoric dissolution (burial)), dolomitization (in different phases), silicification, pyrite and phosphating, as well as mechanical and chemical compaction, fracture development, and porosity. Based on sequence boundaries and facies depth changes, we identify three third-order upward-shallow sedimentary sequences within the carbonate sequences of the Asmari Formation in both the subsurface and surface sections, corresponding to the Early Aquitanian, Late Aquitanian, and Bordigalian ages. Porosity examination reveals that vuggy, moldic, and fracture porosities are the most prevalent types of primary and secondary porosities in the Asmari Formation.