Facies-controlled reservoir modeling of the Upper Paleocene Mabruk limestone reservoir in the northwestern Sirte Basin, Libya: insights into reservoir quality

Abstract This study presents an integrated characterization of the geological and petrophysical properties of the Mabruk Formation, a key reservoir unit exhibiting significant structural complexity and pronounced lateral and vertical facies heterogeneity. Such complexity contributes to uncertainty in reservoir performance, hydrocarbon distribution, and reservoir connectivity. A three-dimensional (3D) facies model of the Mabruk Formation was developed by integrating geological data, wireline log interpretation, and petrophysical analysis to evaluate the spatial distribution of porosity, permeability, and water saturation. The reservoir is dominated by three facies: limestone (~ 47%), calcareous shale (~ 35%), and shale (~ 18%), highlighting the heterogeneous nature of the formation. Porosity ranges from 0.12 to 0.28, while permeability reaches up to 414 mD, indicating the presence of intervals with moderate to good reservoir quality. Water saturation varies between 0.20 and 0.90, with lower values corresponding to zones of superior reservoir properties. The results demonstrate that facies variations, in combination with faulting, exert a primary control on reservoir quality and hydrocarbon distribution. The total estimated original oil in place of the Mabruk reservoir is approximately 115 × 10⁶ stock tank barrels. This integrated geological and petrophysical modeling framework is adaptable to new data and provides a robust tool to support future drilling, reservoir development, and management strategies, thereby helping to reduce uncertainty associated with carbonate reservoir heterogeneity in the Sirte Basin and similar North African reservoirs.