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<p>The Upper Cretaceous sedimentary successions of the eastern Sirte Basin form an important petroleum system, providing both effective reservoirs and reliable seals. Despite their economic significance, high-resolution sedimentologic and petrologic studies of these successions remain limited, particularly regarding their impact on reservoir development and quality. Thus, the present study integrates core, petrographic, and diagenetic examinations to investigate the sedimentological characteristics of the Upper Cretaceous Etla clastic and Lidam evaporite formations in the eastern Sirte Basin, highlighting Etla’s role as a hydrocarbon reservoir and Lidam’s potential as a cap rock. Sedimentologic analyses indicate that the Etla Formation is dominated by quartz and sublithic arenite sandstones with conglomerate, breccia, and anhydrite, whereas the Lidam Formation mainly consists of silty claystone, lithic wacke, dolomite, and minor anhydrite. Core intervals from multiple wells contain diverse sedimentary features, including low-angle tabular cross-bedding, even, inclined, and irregular laminations, flaser bedding, rubble, and occasional mud drapes. Integration of petrofacies and sedimentary features indicates that the Etla and Lidam formations represent two main depositional systems: a fan-delta dominated by debris-flow facies and an evaporitic shoreline comprising mudflat, sabkha, and lagoonal facies. Diagenesis is dominated by quartz overgrowths—particularly in quartz and sublithic arenites—reducing pore connectivity. Kaolinite occurs as pore-filling, replacive, and lining phases with minor clays, hematite, pyrite, and anhydrite, along with limited dissolution and fracture porosity. Finer-grained facies (wackes and silty claystones) commonly show pyrite–hematite replacement and moderate clay development. Reservoir performance is largely governed by depositional architecture, with gravel- and sand-sized debris-flow deposits providing the most favorable conditions for high-quality reservoirs. The fine-grained evaporitic shoreline facies act as tight, baffle-to-seal intervals due to their low permeability. The study establishes a depositional–diagenetic framework that improves understanding of the Upper Cretaceous petroleum systems in the eastern Sirte Basin and helps reduce exploration and development uncertainties in comparable hydrocarbon settings.</p>

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Integrated sedimentologic–diagenetic evaluation of reservoir quality in the Upper Cretaceous Etla clastic and Lidam evaporite formations, eastern Sirte Basin, Libya

  • 期刊论文

  • 发表日期：

    2026年3月5日

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  • Muneer Abdalla,
  • Abdalla Abdelnabi,
  • Husamaldeen Zubi,
  • Saleh Qaysi

摘要

The Upper Cretaceous sedimentary successions of the eastern Sirte Basin form an important petroleum system, providing both effective reservoirs and reliable seals. Despite their economic significance, high-resolution sedimentologic and petrologic studies of these successions remain limited, particularly regarding their impact on reservoir development and quality. Thus, the present study integrates core, petrographic, and diagenetic examinations to investigate the sedimentological characteristics of the Upper Cretaceous Etla clastic and Lidam evaporite formations in the eastern Sirte Basin, highlighting Etla’s role as a hydrocarbon reservoir and Lidam’s potential as a cap rock. Sedimentologic analyses indicate that the Etla Formation is dominated by quartz and sublithic arenite sandstones with conglomerate, breccia, and anhydrite, whereas the Lidam Formation mainly consists of silty claystone, lithic wacke, dolomite, and minor anhydrite. Core intervals from multiple wells contain diverse sedimentary features, including low-angle tabular cross-bedding, even, inclined, and irregular laminations, flaser bedding, rubble, and occasional mud drapes. Integration of petrofacies and sedimentary features indicates that the Etla and Lidam formations represent two main depositional systems: a fan-delta dominated by debris-flow facies and an evaporitic shoreline comprising mudflat, sabkha, and lagoonal facies. Diagenesis is dominated by quartz overgrowths—particularly in quartz and sublithic arenites—reducing pore connectivity. Kaolinite occurs as pore-filling, replacive, and lining phases with minor clays, hematite, pyrite, and anhydrite, along with limited dissolution and fracture porosity. Finer-grained facies (wackes and silty claystones) commonly show pyrite–hematite replacement and moderate clay development. Reservoir performance is largely governed by depositional architecture, with gravel- and sand-sized debris-flow deposits providing the most favorable conditions for high-quality reservoirs. The fine-grained evaporitic shoreline facies act as tight, baffle-to-seal intervals due to their low permeability. The study establishes a depositional–diagenetic framework that improves understanding of the Upper Cretaceous petroleum systems in the eastern Sirte Basin and helps reduce exploration and development uncertainties in comparable hydrocarbon settings.