Source rock evaluation and nature of hydrocarbons in the Khalda Concession, Shushan Basin, Egypt's Western Desert

Abstract

Organic geochemical studies were undertaken on 241 Jurassic–Cretaceous ditch cuttings samples, and 9 gases and 10 crude oils from some productive Mesozoic pay-zone intervals in the Khalda Concession, Shushan Basin, northern Western Desert, Egypt. We aim to investigate source rock characteristics, origin of gases, nature of oils and their inferred source rocks, and to establish genetic relationships.The Middle Jurassic Khatatba Formation and older rocks contain organic-rich, mature, coaly and carbonaceous shales which are the main source for hydrocarbons in Egypt's Western Desert, including the Shushan Basin, which generally contains kerogen Type III with some contribution of Type III/II kerogen.Molecular and isotopic composition indicates that the Khalda gases are of thermogenic origin. A mature (>0.6–>2.0%Ro) source rock with terrigenous organic matter (kerogen Type III) was identified as a precursor of wet thermogenic gases in the Shushan Basin.Geochemical results indicate that the oil samples were derived from a source rock deposited mainly under oxic conditions and containing terrigenous organic matter. Biomarker data indicate that paraffinic oils and condensates from the Shushan Basin were derived from mature source rocks within the oil window. The light hydrocarbon data suggests that the analyzed oils can be classified into two groups as a result of evaporative fractionation and maturation. This signal of a secondary reservoir transformation, which is not revealed by biomarker analysis, emphasizes the importance of integrating biomarker and light hydrocarbon data to understand variations in the chemical composition and origin of oils.