Evolution of petroleum generation and expulsion of the oil-source rock in the north-western Say’un-Masilah Basin as inferred from 1D basin models of a single well (Al-Qarn-01)

The Madbi Shale Formation is the main oil-source rock for conventional petroleum extraction in the east-central Say’un-Masilah Basin. This study explores the generation and expulsion potential of oil from the Madbi source rock system in a deep well location (Al-Qarn-01) in the north-western Say’un-Masilah Basin using geological and geochemical modelling. One-dimensional (1D) basin models were constructed to the estimate thermal regime in the basin and the evolution of oil cracking and expulsion from the organic-rich intervals in the Madbi Formation over the geological time. In the studied Al-Qarn-01 well, the organic-rich intervals in the Madbi Formation are thermally mature, ranging from peak- to late-mature oil window stages; thus, half or more of the kerogen was converted to oil at these maturity stages. The basin modelling results of the studied well (Al-Qarn-01) show that oil was generated and expelled from Madbi source rock intervals in two main phases according to the conversion ratio (TR %) of kerogen. The main conversion of kerogen to oil (TR = 10–50%) occurred between Late Cretaceous and Early Oligocene (80–33 Ma) periods, corresponding to the peak-oil window (0.70–1.00 Easy %Ro). Furthermore, significant amounts of oil were expelled from the source rock, which subsequently migrated into the overlying reservoir rocks in the Early Oligocene time during the initial Tertiary rifting. The late-mature oil window (1.00–1.10 Easy %Ro) commenced during this time, with TRs of 50–77%.