Petroleum Systems in the Geisum Area, South Gulf of Suez, Egypt: Insights from 1D Basin Modeling and Fluid Geochemistry

ABSTRACT This study aims to unravel the petroleum system(s) of the Geisum area within Egypt's prolific Gulf of Suez rift basin through investigating the hydrocarbon potential of source rocks and genetic origin of petroleum plays. A total of 135 cutting samples were analyzed using organic geochemical procedures, including Rock‐Eval pyrolysis and vitrinite reflectance (%Ro), whereas 1D basin models were applied to simulate the basin's burial and thermal histories. Gas chromatography‐flame ionization detector (GC–FID), GC–mass spectrometry (GC–MS), and GC‐combustion–isotope ratio mass spectrometry (GC–C–IRMS) were conducted on 12 crude oils and six source rock extracts to assess bulk geochemical characteristics, biomarkers, and isotopic compositions of parent source rocks. The 1D‐modeling results along the NW–SW profile suggest that the Geisum area is a productive province, including Brown Limestone as the primary source (TR = 85%–95%), whereas Matulla/Wata contributed moderately (TR = 25%–44%), and Rudeis only expelled hydrocarbons in the southern compartment. Furthermore, heat flow (HF) rather than erosion predominantly controls thermal maturity, with peak generation occurring during the Late Miocene (7–5 Ma) in the northern and southern sectors. Structurally, the area is divided into three compartments due to Oligocene rifting, which influenced hydrocarbon migration pathways. The multivariate chemometric analysis reveals three genetically distinct oil families distributed across different oilfields in the Gulf of Suez. Family I, in the Geisum oilfield, likely derives from carbonate‐rich Sudr/Brown Limestone (high gammacerane, C 29 sterane dominance, depleted δ 1 3 C). Family II, from the same oilfield, is attributed to marine Matulla shales (moderate gammacerane, C 27 steranes, similar δ 1 3 C). Family III, from the Tawila oilfield, appears sourced from mixed marine/lacustrine Rudeis sediments (low gammacerane, C 28 steranes, enriched δ 1 3 C).