Abstract
The Cretaceous source rocks of the Sirt Basin, Libya, constitute one of the principal hydrocarbon-generating systems responsible for the basin's exceptional petroleum endowment. Despite decades of exploration and production, significant uncertainties remain regarding the timing, extent, and efficiency of petroleum generation and expulsion across different structural provinces of the basin. This study presents an integrated regional assessment of the petroleum generation and expulsion history of the Cretaceous source rocks through the combination of organic geochemical analyses and basin modeling techniques. The objective is to quantify the spatial and temporal evolution of hydrocarbon generation, identify the principal source kitchens, and evaluate the controls governing petroleum expulsion and migration within the basin. The study integrates geological, geochemical, and subsurface information from representative exploration and development wells across the Sirt Basin. Source rock evaluation includes Total Organic Carbon (TOC), Rock-Eval pyrolysis, kerogen typing, vitrinite reflectance (Ro), biomarker geochemistry, and kinetic parameters to characterize source rock quality, organic matter type, and thermal maturity. These data are calibrated with one-dimensional and two-dimensional basin models that reconstruct burial history, thermal evolution, hydrocarbon transformation ratios, generation rates, and expulsion efficiency. The models incorporate regional stratigraphy, tectonic evolution, sedimentation history, heat-flow variations, and erosion events to simulate the evolution of the Cretaceous petroleum system through geological time. The modeling results demonstrate that petroleum generation was initiated following progressive burial during the Late Cretaceous, with hydrocarbon generation intensifying throughout the post-Cretaceous time as rapid subsidence increased thermal maturity within the basin depocenters. Peak oil generation occurred across the deepest structural troughs where source rocks reached optimum thermal maturity, while continued burial locally resulted in secondary cracking and wet gas generation. Petroleum expulsion closely followed the main phase of hydrocarbon generation after transformation ratios exceeded critical thresholds, leading to efficient migration into adjacent structural and stratigraphic traps. In contrast, structurally elevated regions and basin margins remained thermally immature or only marginally mature, resulting in limited hydrocarbon generation and expulsion. Regional variations in source rock richness, kerogen type, burial depth, and heat-flow history produced significant differences in expulsion efficiency and hydrocarbon charge among the basin's petroleum systems. The integrated geochemical and basin modeling approach provides a robust reconstruction of the generation and expulsion history of the Cretaceous source rocks and highlights the dominant controls on petroleum system evolution within the Sirt Basin. The identification of mature source kitchens, timing of hydrocarbon charge, and migration pathways significantly improves the understanding of exploration risk and remaining resource potential. These findings provide an important regional framework for future petroleum exploration, basin-scale resource assessment, and the evaluation of both conventional and unconventional hydrocarbon opportunities in one of North Africa's most prolific petroleum provinces.