Reservoir quality drivers in the Oligo-Miocene Asmari Formation, Dezful Embayment, Iran: Facies, diagenesis, and tectonic controls

Abstract

The Oligo-Miocene Asmari Formation in the Shadegan Oil Field, located in the Dezful Embayment in southwestern Iran, is renowned for its complex geological characteristics in the Middle East. This study systematically investigates the drivers of reservoir quality, emphasizing the interplay between geological settings, depositional environments and facies, diagenetic processes, and tectonic activities that shape porosity and permeability. Based on the sedimentary architecture and analysis of the facies associations this formation contains a diverse assemblage of carbonate and siliciclastic lithofacies (twenty-six carbonate microfacies and six siliciclastic facies association), revealing a mixed depositional system influenced by siliciclastic influx, climatic and sea-level fluctuations, and tectonic movements. Extensive core and petrophysical data analysis were utilized to identify hydraulic flow units (HFUs) and optimize reservoir zonation using advanced analytical techniques, including machine learning algorithms. Four hydraulic flow units (HFUs) were determined and evaluated against lithology and petrophysical values: baffle unit (HFU1), normal unit (HFU2), permeable unit (HFU3), and high permeable unit (HFU4).

Key findings underscore the critical role of fractures in enhancing reservoir productivity, significantly impacting hydrocarbon recovery rates. Additionally, the analysis of diagenetic processes such as dolomitization, cementation, and dissolution reveals their dual impact—either enhancing or degrading reservoir quality. The study concludes that effective reservoir characterization depends on integrated methodologies, which combine traditional geological assessments with modern data processing techniques. This approach enhances exploration and production strategies in complex carbonate reservoirs. Ultimately, this research offers new insights into a comprehensive framework for understanding the drivers of reservoir quality in the Asmari Formation and their implications for hydrocarbon development.