Subdividing a Cretaceous Carbonate Reservoir in the East Mediterranean Sea, Egypt, Based on Petrographical Characteristics: A Case Study

Document Type : Review Article

Authors

1 Belayim Petroleum Company

2 Department of Geology, Faculty of Science, Al-Azhar University

Abstract

Reservoir studies necessitate a consistent and repeatable classification of carbonate lithofacies, serving as a fundamental input for constructing depositional, diagenetic, and reservoir models. Traditionally, the Dunham and Folk Systems have been relied upon to fulfill this requirement. In the Cretaceous carbonate reservoir of the Zohr Field, the reservoir is subdivided into four sub-reservoirs based on biostratigraphic and sedimentological analyses. These reservoir levels, from top to bottom, are designated as Level 1, Level 2, Level 3, and Level 4. These units exhibit variations in thickness, facies, and petrophysical properties, often leading to differences between wells. In many instances, it is challenging to correlate the log patterns observed in these units. This is due to lateral variations in depositional facies, syn-depositional changes, and post-depositional diagenetic processes. This study investigates these Cretaceous-aged carbonate lithofacies in the Zohr Field by employing the highly detailed and comprehensive approach of petrographical analysis which allows for more accurate classification of these rocks compared to conventional methods. It examines a spectrum of synthetic rock textures, natural lithologies, and thin section textures derived from core samples, side-wall cores, and ditch cuttings. As a result, the outcomes of this petrographical analysis have helped in refining the present reservoir boundaries. The modified boundaries derived from petrographic analysis have been adopted, thereby facilitating the development of more realistically constrained depositional, diagenetic, and reservoir models. Furthermore, the results have been utilized to create texture and porosity curves, enabling a detailed and accurate correlation among different wells and reservoir levels in the Zohr Field.

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