Formation evaluation using conventional and special core analyses: Belayim Formation as a case study, Gulf of Suez, Egypt

Abstract

The present study aims to throw the light on the importance of the conventional and special core analyses in the integration with the petrographical studies for the formation evaluation of the reservoir rocks. The petrographical studies include the microfacies analysis and studying the diagenetic factors that predominated during the diagenetic history of the Belayim rock sequence in the study area. Two zones of Belayim Formation in the onshore Belayim oil field (the upper level (zone IIA) represents Hammam Faraun member and the lower one (zone IV) represents Sidri member) were studied. The measured routine core analyses data includes porosity (helium and summation fluids), density (grain and bulk), permeability (horizontal and vertical) and fluid saturations (oil and water). In addition, the formation resistivity factor, irreducible water saturation, Archie’s parameters (a, m and n), liquid permeability, relative permeability, wettability, the pore throat distribution, as well as the porosity and permeability measured under high pressure were measured as a special core analyses procedure. From the integration of the aforementioned petrographical and petrophysical studies, the Belayim Formation can be discriminated into three petrophysical facies (Facies-1, Facies-2 and Facies-3) described petrographically as (1) Facies-1 (argillaceous subfeldspathic arenite microfacies), (2) Facies-2 (siliceous quartz arenite microfacies) and (3) Facies-3 (dolomitic sublithic arenite microfacies). The petrophysical Facies-2 (siliceous microfacies) is characterized by the best reservoir properties (rank III, very good average porosity, very good permeability, fair to very good reservoir quality index (RQI) and relatively poor to good flow zone indicator (FZI), neutral to moderately oil wet and more than 75% macropores and mesopores). On the other side, samples of the petrophysical Facies-1 (argillaceous microfacies) have the lowest reservoir potential (rank VI, poor average porosity, poor to fair permeability, poor to impervious RQI and relatively poor to fair FZI and more than 50% micropores and nanopores). Therefore, it is recommended to use the conventional and special core analyses data in the integration with the petrographical studies as a good procedure for the formation evaluation and discrimination of the reservoir sequence into different flow units.