Reservoir Rock Typing for Heterogeneous Sandstone: A Case Study of Nubia Sandstone, Gulf of Suez, Egypt

The pre-Cenomanian Nubia sandstone is considered as one of the most productive reservoirs in the Gulf of Suez, Egypt. Determination of its reservoir rock type (RRT) is a crucial process in reservoir characterization and modeling, especially when the reservoir is extremely heterogeneous. In this study, an effort was made to bridge the gap between various techniques to determining RRT, which include lithofacies, traditional methods (x-y crossplots), and machine learning (ML). To accomplish this, the objectives of this study were accomplished through the utilization of sedimentological core description, routine core analysis, and conventional logging data from two wells (well A and well B) in the southern Gulf of Suez. The results show that the complete Nubia interval in the southern Gulf of Suez can be distinguished into seven distinct lithofacies (LF1-LF7). The first six lithofacies are comprised of different types of sandstones, while the seventh is related to mudstone. The results show also that the fault-cutting, rather than stratigraphic reasons, was primarily responsible for the difference in Nubia thicknesses between the two studied wells. It is likely that the lower three lithofacies were separated from one another by unconformity surfaces. The traditional techniques used to predict the RRTs show that the normalized reservoir quality index (NRQI) was the most appreciated method to predict the Nubia rock types. On the other hand, K –means clustering and self-organizing maps (SOM) techniques based on raw logging data and principal component analysis (PCA) can properly predict the Nubia reservoir rock types when correlated with the Ward’s method, which is based on the core data. The reservoir rock quality ranged from poor to very good, with a domination of moderate reservoir quality in well A and very good reservoir quality in well B. This discernible difference in reservoir quality between the two wells was probably attributed to the consequences of the post-deposition diagenesis processes and the variation of the sandstone texture.