Overview of the Late Jurassic Madbi-Sab'atayn petroleum system in the Marib Concession, northwestern Sab'atayn Basin (Yemen): hydrocarbon from source to trapping

The Marib Concession in the northwestern Sab'atayn Basin is the most conventional petroleum exploration activities. Although the Marib Concession is an established hydrocarbon province due to the accumulation of Mesozoic sediments some of which act as good source and reservoir rocks, still there is a gap in developing a better understanding the petroleum system of the region. This study identifies the characterization and effectiveness of the Late Jurassic Madbi-Sab'atayn petroleum system for the Marib Concession and reveals Kimmeridgian-Tithonian Madbi Shales and Tithonian Alif sandstones as the source and reservoir rocks, respectively. To analyze its source rock and reservoir characteristics, model the generation and migration histories, and outline the entrapment style and effective seals of the petroleum system, integrated geochemical and geological modeling techniques were used. The shale intervals within the Lam and Meem Members of the Late Jurassic Madbi Formation are considered to be the main source rocks in the Marib Concession and characterized by fairly high total organic content (TOC%) of up to 9.0%, whereas the hydrogen index (HI) ranges from 50 to 595 mg HC/g TOC, indicating that the kerogen types contained within these shales are mainly Type II and mixed Type II/III, with a significant amount of Type III. A wide range of vitrinite reflectance values (0.50–2.61 R 0 %) is indicative of the Madbi shales maturity and illustrates that the Madbi source rock is currently within the peak oil to gas window. Geochemical oil-source rock correlation analyses propose that the hydrocarbon’s regional distribution in the Marib Concession was mainly derived from the Kimmeridgian age Madbi shales. The reservoir units are discovered in various stratigraphic sequences of Late Jurassic period, including Alif and Seen Members of the Sab'atayn Formation as well as Lam Member of the Madbi Formation. Still, the sandstones of the Alif Member of the Sab'atayn Formation acting as the primary productive reservoir within the studied Marib Concession. The best reservoir quality of the Alif sandstones is characterized by high porosity and permeability values up to 33% and 10,000 mD, respectively. The Tithonian salt and shales within the Safir Member of the Sab'atayn Formation represent good seal rocks that underlie the hydrocarbon reservoir rocks in Marib Concession. The main tectonic development within the Marib Concession in the northwestern Sab'atayn Basin is occurred as Late Jurassic to Early Cretaceous rifting during the Gondwana supercontinent and separation of Africa–Arabia and Madagascar–India and played a vital role in designing the petroleum play. Structural features such as horst, tilted fault blocks, and few stratigraphic traps are the main trapping mechanisms resulting from the Late Jurassic to Early Cretaceous rifting episodes. Both burial and thermal basin models reveal that the hydrocarbon generation within the Madbi active pod was initiated during the Late Jurassic period. The highest rate of hydrocarbon expulsion was attained in the Late Cretaceous time. In contrast, the migration of hydrocarbons continued since the Early Cretaceous period, most likely during the Hauterivian-Barremian ages. The hydrocarbon from the Madbi source rock, reached the trapping site via vertical migration paths through the faults due to an episode of rift during the Early Cretaceous period. This study provides important petroleum system elements for evaluating hydrocarbon resources in the Marib Concession of the northwestern Sab'atayn Basin, which is beneficial for further and exploration and better resources exploitation.