Linking petrophysical heterogeneity and reservoir rock-typing of the post-rift shallow marine siliciclastics to their depositional setting: The Upper Cretaceous Bahariya reservoirs, north Western Desert, Egypt

Abstract

The upper Cretaceous clastic facies of the Bahariya Formation host the main reservoir intervals in the north Western Desert (NWD) of Egypt. These clastics were deposited in a parallic depositional environment characterized by different scales of reservoir heterogeneities. However, the link between these heterogeneities and the depositional setting of the reservoir facies is still blurred. In this study, we investigate a highly-heterogeneous reservoir facies of Bahariya Formation in Yasser Field wells, NWD in order to construct a predictive framework for the distribution of the best reservoir rock types (RRTs) and flow zones. Seismic stratigraphy was integrated with core sedimentology to understand the depositional architecture of the reservoir facies. Moreover, conventional core analysis and wireline logs were interpreted to evaluate the scales of lithological and petrophysical heterogeneities in the different RRTs.

In the studied Yasser Field, the Bahariya Formation consists of tidal facies deposited in a wide range of tidally-influenced conditions. The seismic facies varies greatly with variation in the tidal regime. Best reservoir rock types RRTs are associated with tidal channels and amalgamated tidal bars (RRTI). RRTI rocks represent the main fluid flow conduits in the studied Bahariya reservoir. Lithological and petrophysical heterogeneities are more prominent in the tidal mud flat and mixed tidal flat facies which form RRTIII rocks. Linking seismic with sedimentary facies enabled us to predict the distribution of the best reservoir flow zones in the study region. The present results establish a framework for predicting the optimum reservoir quality facies based on integrating seismic, sedimentary and petrofacies. This framework could be applied in analogous tidally-influenced reservoir facies with high depositionally-controlled pore system heterogeneity.