Significance of core analysis and gamma-ray trends in depositional facies interpretation and reservoir evaluation of Cenomanian sequence, Alam El-Shawish East Oil Field, North Western Desert, Egypt

Abstract

The present paper aims to evaluate the sedimentological model of the study Cenomanain sequence in terms of electrofacies interpretation and depositional facies architecture to reveal the spatial distribution of the reservoir facies characterization. The influence of depositional lithofacies types on reservoir characterization of the Cenomanian Bahariya Formation and Abu Roash “G” Member was investigated using the integration of available core data and petrophysical evaluation from seven wells in Alam El-Shawish East Oil Field, North Western Desert, Egypt. Careful log interpretation and correlation enable differentiation of the study sequence into ten sedimentary cycles. The stacking of the recognized facies types in the available cored interval, form fifteen depositional facies associations from which fluvial, estuarine and shoreline-shallow shelf models were constructed. This facies information has been used to calibrate the log response, particularly the gamma-ray trends, as an aid to interpret the depositional environment of the non-cored intervals. However, the generalized log pattern shows micro-variations in log shape and trend based on the location relative to depositional environment and consequently major modified gamma-ray patterns were proposed depending on the cored facies architecture. Therefore, precautions must be taken into consideration in extrapolating the present patterns to any similar heterogeneous sequence due to the effects of variable diagenetic and facies type constraints on log response. It is indicated that hydrocarbons could be accumulated within shoreface and barrier tidal inlet complex near or within the depositional sequence boundary surfaces along the Upper Bahariya Member and the upper unit of Abu Roash “G” Member. The associated fine siliciclastics (mudstone and shale) of tidal lagoon and/or shoreface delta facies may be acted as local source rock and trap seals. Based on reservoir characterization data supplemented by well logs interpretation of the cored and non-cored intervals, further reservoir beds could be recommended as potential prospecting targets.