Static reservoir characterization of shallow marine carbonate rocks: A case study from the Late Triassic-Early Jurassic Sarki Formation, NE Iraq

This study investigates the reservoir properties of the Late Triassic-Early Jurassic shallow marine carbonate Sarki Formation outcrop, specifically in the Zarwan section of northeastern Iraqi Kurdistan. The lithology of the studied section comprises dolomite, dolomitic limestone, recrystallized breccia and thin beds of marls, with a formation thickness of approximately 115 m. Various techniques, including microscopic study, core plug analysis and scanning electron microscopy (SEM) were employed to assess reservoir properties. The Sarki Formation consists of diverse pore types, including vuggy, moldic, intraparticle, interparticle, fracture, intercrystalline, stylolitic and microporosity. Identified diagenetic processes include early dolomitization, compaction (physical and chemical), cementation (granular, blocky, and drusy cements), micritization, dissolution, silicification, neomorphism, late dolomitization, and fracturing. Petrographic analysis indicated a porosity average of 2% in the lower part of the formation and 6% and 9.5% in the middle and upper parts, respectively. A scanning electron microscopy (SEM) study confirmed similar porosity values with micropore sizes in the studied section. Core plug analysis results were roughly aligned with optical assessments, revealing porosity values of 2%, 6%, and 10% for the lower, middle, and upper parts, respectively. Overall, the Sarki Formation exhibited negligible to fair porosity ranges. Permeability measurements values averaged 0.01 md, 0.02 md, and 0.13 md for the lower, middle, and upper parts respectively, indicating a poor to fair permeability range. The upper part of the formation was deemed to have fair reservoir quality due to fewer observed diagenetic processes than the middle and lower parts, although permeability may be relatively low. In contrast, the lower and middle parts displayed poor reservoir characteristics, suggesting limited potential in the context of the petroleum reservoir.