Facies and NMR-based petrophysical analyses of the Apollonia unconventional gas reservoir: A case study from the BED–9 field, Abu Gharadig Basin, North Western Desert, Egypt

The Early Paleocene to Middle Eocene Apollonia Formation in the BED ‒ 9 field has been particularly interesting for unconventional hydrocarbon exploration since its discovery in 2006. However, the multiscale compositional and diagenetic inconsistencies present challenges for its characterization. This study aims to evaluate the petrophysical properties of the Apollonia Formation to locate the sweet-spot intervals. Moreover, it seeks to investigate reservoir rock types (RRTs), depositional settings, and the impact of diagenesis on reservoir quality. The findings of this study are as follows. 1) The Apollonia A5 and C1 units are identified as "sweet-spot" intervals. Their effective porosity ranges from 18 % to 35 %, average permeability varies from 0.1 to 2.0 mD, and water saturation falls between 40 % and 50 %, indicating good reservoir quality. 2) High-order eustatic sea-level changes and repetitive climatic change cycles significantly influence the alternating carbonate productivity and dilution cycles. Five distinct RRTs are classified, denoting a gradational facies change from clean, argillaceous, and carbonaceous chalky limestone to marl and interbedded shale intervals. 3) Interpreting the electro-facies responses, collated with microfacies variations and faunal content, deepens our understanding of the depositional environment, which extends from the inner- to outer-shelf setting. 4) The diagenetic processes have a dual impact that enhances and diminishes the reservoir quality. Finally, the gap in evaluating the petrophysical characteristics of all the Apollonia members has been addressed based on integrating the petrophysical and facies analysis for A, B, and C members. The Apollonia Formation has unique characteristics as an unconventional hydrocarbon resource. • Electro-facies patterns reveal the history of deposition and diagenesis impact. • The depositional environment of the Apollonia carbonates ranges from outer shelf to inner-shelf setting. • NMR well-logging data used to compute petrophysical reservoir properties.