Depositional cycles of the Lower Miocene Rudeis Formation (southwestern offshore margin of the Gulf of Suez, Egypt): Implications for reservoir evaluation

摘要

The Lower Miocene Rudeis Formation in the Zeit Bay Field (Gulf of Suez, Egypt) has been studied by analysis of cores from six boreholes. The objective was to detail the sedimentary cycles in the formation and their implications for the reservoir characteristics, as well as to obtain a more detailed insight into the precise age by establishing a foraminifer zonation. The formation, which was found to be some 60-191 m thick, is composed almost exclusively of various types of carbonates. These contain foraminifers that prove a Burdigalian age, and that also provide insight into the depositional environments, which turned out to form three belts. These belts represent an intertidal lagoon, barrier shoals, and a reef complex, respectively, indicating a down-dip depositional profile of a shallow marine rimmed carbonate shelf. Analysis of the cyclicity pattern of the Rudeis Formation, supported by fades analysis and CycloLog curves, makes it possible to distinguish three superimposed 3rd-order depositional cycles, which are subdivided into several higher-order cycles that are strongly controlled by eustatic sea-level fluctuations. A set of lithofacies isopach maps has been constructed for these cycles with the objective to facilitate interpretation of the spatial distribution of the reservoir quality for hydrocarbons. The maps show that the reservoir quality of the Rudeis Formation is heterogeneous because of the highly variable characteristics of the various lithofacies types.