Pore‐Facies‐Based Reservoir Quality Evaluation of the Ilam Formation Tight Carbonates Through Integrated Digital Rock and MICP Analyses in the Abadan Plain, Zagros Basin, Iran

ABSTRACT The Ilam Formation in the Abadan Plain represents a tight carbonate reservoir whose performance is strongly influenced by complex pore systems and diagenetic overprinting. This study integrates digital rock analysis, mercury injection capillary pressure (MICP), and petrographic observations to characterize pore types, pore‐throat size distributions, and pore‐network connectivity, and to develop a pore‐facies‐based framework for evaluating reservoir quality. Digital rock physics (combining micro‐scale scanning electron microscopy [SEM] imaging for microporosity and computed tomography (CT) scanning for macro‐ and meso‐pore systems) were used to quantify the pore architecture and tortuosity, whereas MICP data provided pore‐throat size spectra and capillary pressure parameters (including reservoir grade [RG], R35, Pd, Pt, Swanson, and mean hydraulic radius [MHR]). Petrographic and mineralogical analyses constrained the roles of texture, diagenesis, and clay minerals in controlling pore evolution. Four pore facies (PF1–PF4) were distinguished, each with distinct petrophysical signatures. Pore Facies 2 exhibits the highest porosity and permeability, well‐developed moldic and vuggy pores, and the most effective pore connectivity, and thus represents the best reservoir interval. Pore Facies 1 shows moderate storage capacity but limited flow due to restricted connectivity, whereas Pore Facies 3 and especially Pore Facies 4 are characterized by smaller pore throats, higher capillary entry pressures, and poor permeability, leading to severely restricted fluid flow. The results demonstrate that reservoir quality in the Ilam tight carbonates is governed primarily by pore‐throat geometry and connectivity, rather than by bulk porosity or density alone. Although tortuosity likely contributes to permeability reduction in these tight carbonates, tortuosity was not directly quantified in this study and is therefore discussed only qualitatively. Diagenetic processes (compaction, cementation, and dissolution) and clay mineralogy (including illite, kaolinite, and montmorillonite) exert a first‐order control on the present‐day tight character of the formation. This integrated workflow provides a robust basis for rock typing and reservoir quality prediction in the Ilam Formation and underscores the need for multiscale characterization in tight carbonate systems. The pore‐facies framework developed here can support improved petrophysical interpretation and guide targeting of the most promising intervals, particularly those associated with Pore Facies 2.