CRUDE OIL GEOCHEMISTRY AND SOURCE ROCK POTENTIAL OF THE UPPER CRETACEOUS – EOCENE SUCCESSION IN THE BELAYIM OILFIELDS, CENTRAL GULF OF SUEZ, EGYPT W. Sh. El Diasty *1 , S.Y. El Beialy 1 , A. R. Mostafa 2 , A. A. Abo Ghonaim 1 and K. E. Peters 3 This study evaluates the petroleum potential of source rocks in the pre-rift Upper Cretaceous – Eocene succession at the Belayim oilields in the central Gulf of Suez Basin. Organic geochemical and palynofacies investigations were carried out on 65 cuttings samples collected from the Thebes, Brown Limestone and Matulla Formations. Analytical methods included Rock-Eval pyrolysis, Liquid Chromatography, Gas Chromatography and Gas Chromatography – Mass Spectrometry. Four crude oil samples from producing wells were characterised using C 7 light hydrocarbons, stable carbon isotopes and biomarker characteristics. The results showed that the studied source rocks are composed of marine carbonates with organic matter dominated by algae and bacteria with minimal terrigenous input, deposited under reducing conditions. This conclusion was supported by n-alkane distributions, pristane/ phytane ratios, homohopane and gammacerane indices, high concentrations of cholestane, the presence of C 30 n-propylcholestanes, and low diasterane ratios. The source rocks ranged from immature to marginally mature based on the Rock-Eval T max together with biomarker maturity parameters. The analysed crude oil samples are interpreted to have been derived from source rock intervals within the Eocene Thebes Formation and the Upper Cretaceous Brown Limestone. The similarity in the geochemical characteristics of the crude oils suggests that there was little variation in the organofacies of the source rocks from which they were derived. 1 Mansoura University, Faculty of Science, Geology Department, Mansoura 35516, Egypt. 2 Alexandria University, Faculty of Science, Department of Environmental Sciences, Alexandria, Egypt. 3 Schlumberger, Mill Valley, CA 94944 & Geological and Environmental Sciences Department, Stanford University, Stanford, CA 94305, USA. * Corresponding author, waleedshukry2006@yahoo.co.uk Key words: Belayim oilields, Gulf of Suez, Egypt, source rocks, petroleum potential, Thebes Formation, Brown Limestone Formation, Matulla Formation, palynofacies, biomarkers. INTRODUCTION The Belayim development concession in the central Gulf of Suez, located 165 km SE of Suez City, comprises the Belayim Land and Belayim Marine oilfields (Fig. 1), discovered in 1955 and 1961 respectively. The Belayim Marine field, the first offshore ield discovered in Egypt, is located about 9 193 Journal of Petroleum Geology,Vol. 38(2), April 2015, pp 193-216 © 2015 The Authors. Journal of Petroleum Geology © 2015 Scientiic Press Ltd www.jpg.co.uk