Integrated seismic stratigraphic, sedimentological and petrophysical approaches for characterizing the Cenomanian reservoirs in transitional highs of north Western Desert intra-cratonic rift basins, Egypt

Abstract

The Cenomanian Bahariya Formation is the most prolific hydrocarbon reservoir within the Mesozoic intra-cratonic rift basins of the Egyptian Western Desert. However, it remains under-explored in the transitional structural highs bordering these basins. These transitional regions host thin hydrocarbon pay zones in the sandstones of the Bahariya Formation. These sandstones exhibit pronounced petrophysical heterogeneity, which poses significant challenges to reservoir characterization and prediction, and their depositional characteristics and controls on the reservoir facies distribution have never been investigated. This study employs an integrated approach utilizing seismic stratigraphy, sedimentary facies analysis and petrophysics to establish the relationship between the Bahariya depositional patterns, reservoir rock types, and hydraulic flow units. Understanding these relationships is essential for assessing reservoir performance and identifying high-quality reservoir intervals for future exploration and production in these transitional regions. The studied core intervals comprise the Upper Bahriya reservoirs in two wells (Wadi El-Rayan-3X “WR-3X″ and Rayan-3X “R-3X”). The cored intervals consist mainly of sixteen sandstone, mudstone and siltstone lithofacies that were grouped into nine facies associations (FA) deposited in a muddy tide-dominated estuarine environment. Sandstone lithofacies were preferentially accumulated in narrow (<1 km width) tidal channels (FA2) and sub-tidal bars (FA3). The sandstones of FA2, FA3 were classified as reservoir rock types (RRTs) 1 and 2 (RRT1, RRT2) with best reservoir characteristics and contribute to more than 90 % of the flow capacity of the Upper Bahariya reservoir. Conversely, mixed tidal flats (FA1) and intertidal sand bars (FA4) exhibit the poorest reservoir quality with pore system dominated by micropores and mesopores and act as effective fluid flow barriers. Petrophysical heterogeneity analysis indicates that sandstone lithofacies deposited within the outer estuarine tidal channels and subtidal bar environments exhibit the lowest degree of pore system heterogeneity. These facies are characterized by the dominance of well-connected macropores. The present results underscore the inherent heterogeneity of tide-dominated estuarine systems, where rapid lateral and vertical facies transitions, driven by fluctuating tidal energy and sediment supply, create complex reservoir architectures. Despite this complexity, the study demonstrates that higher-quality reservoir facies tend to preferentially accumulate in zones subjected to stronger tidal currents—specifically in the outer estuarine domain.