Tidal facies analysis and 3D static modeling of the Cenomanian Lower Bahariya reservoir, Qasr Field, North Western Desert, Egypt

Abstract

Facies heterogeneity of the Lower Bahariya sandstone reservoir in the Qasr Field led to challenges in the hydrocarbon exploration and field development. In this study, we integrated sedimentological and petrophysical analysis of conventional core data and wireline logs to construct a 3D static model that predicts the reservoir facies and properties variations in the study area. Detailed sedimentary facies analysis allowed to define eleven sedimentary facies types of three main facies associations: tidal channel, tidal sand bars, and tidal flat complex including bioclastic carbonate accumulations. These facies developed within a transgressive tide-influenced estuarine system. Porosity-permeability data of the interpreted facies reveals that both the tidal sand bars and channels are of good reservoir quality in comparison to the tidal flat heterolithics, and the carbonates that are non-reservoir facies. Both the lower parts of the tidal sand bars and the upper parts of the tidal channels show a relatively lower reservoir quality (ɸ<13 %, K < 1mD) due to increased argillaceous and calcareous cement content. Spatial distribution of the reservoir properties in the 3D geo-cellular static model confirms that the main producing tidal sand bars extend NW-SE, parallel to the fault system. These bars have an excellent reservoir quality in the west that deteriorates towards the east associated with facies change to heterolithic tidal flat facies. Hydrocarbon accumulation was identified within the central part of the study area, particularly within the tidal sand bar facies. The findings of this study shed light on the Lower Bahariya lateral and vertical reservoir distribution and quality, reducing uncertainty in the field development, and providing applicable knowledge for similar heterogeneous tidal hydrocarbon reservoirs.