Evaluation of Cretaceous Source Rocks and Hydrocarbon Correlation in the Beni Suef Basin, Western Desert, Egypt: Biomarkers and Gas Geochemistry Perspective

Abstract

This study explores the geochemical characteristics of Cretaceous source rocks, crude oils, and natural gases in the Beni-Suef Basin, Western Desert, Egypt, with the aim of better understanding oil–source rock and gas–source rock relationships. To achieve this, an integrated approach was used, combining Rock-Eval pyrolysis, total organic carbon (TOC) analysis, vitrinite reflectance measurements, whole-oil gas chromatography, gas chromatography–mass spectrometry (GC–MS) biomarker analysis, stable carbon isotope analysis of natural gases, and one-dimensional burial and thermal maturity modeling. These methods were applied to evaluate organic matter type, thermal maturity, hydrocarbon origin, timing of hydrocarbon generation, and possible migration pathways. The results show that the Abu Roash (F) interval is the most promising source rock unit, with TOC values reaching up to 3.45 wt.% and hydrogen index values as high as 485 mg HC/g TOC. The geochemical data indicate the presence of mixed Type II/III kerogen within the early to peak oil generation window. Biomarker evidence suggests deposition under mainly suboxic conditions with a mixture of marine and terrestrial organic matter input. Oils from the Abu Roash (G) reservoir display clear geochemical similarities to extracts from the Abu Roash (F) interval, supporting a genetic relationship, while the Kharita oil shows a different composition that points to a stronger terrestrial influence. Natural gas composition and carbon isotope data (δ¹³C₁ ≈ −45 to −43.5‰) indicate thermogenic, oil-associated gas formed within the oil to early gas window. The δ¹³C₂–δ¹³C₃ maturity trend suggests gas generation at maturity levels equivalent to approximately 0.7–0.9 %Ro. Burial and thermal maturity modeling further indicate that the Abu Roash–Kharita succession entered the oil window and reached early gas-window conditions during progressive burial, supporting the integrated geochemical interpretation. The close similarity between gases from the Abu Roash (F) interval and those found in the Abu Roash (G) reservoir suggests vertical migration from source to reservoir. Overall, these results provide a clearer and more integrated picture of the Cretaceous petroleum system in the Beni-Suef Basin and offer useful insights for hydrocarbon exploration in the Western Desert of Egypt. However, the study is limited by the relatively small number of analyzed samples and the use of a one-dimensional burial model, which may not fully capture lateral migration pathways and basin heterogeneity.