Oil source rock characteristics of the pelagic carbonates in the Shabwah depression, southeastern Sabatayn Basin, Yemen

Bituminous lime mudstone from the Late Tithonian--Early Barremian Naifa Formation was collected from five wells in the Shabwah depression of the southeastern Sabatayn Basin for basic organic geochemical analyses. The collected samples’ nannofossil contents were also studied. The current study preliminarily evaluated the nature of the organic matter regarding the richness and type of organic facies and their relation to oil generation potential. Most of the lime mudstone samples are organically rich and include favorable source rocks, as indicated by the high TOC content of up to 1 wt%. The presence of the warm-water index nannofossil taxa Watznaueria barnesae suggests warm climate conditions, thereby contributing to high bioproductivity that consequently enhanced organic richness. The samples are also hydrogen rich, with HI values between 302 and 740 mg HC/g TOC, resulting in two dominant organic facies of kerogen Types I and II, and are consistent with high bioproductivity of phytoplankton algae in warm-water conditions during deposition. Both geochemical maturity values T max and PI indicate that the bituminous lime mudstones are at different thermal maturity levels and range from immature to early mature stages of the oil generation window. This implies that the bituminous lime mudstones were not buried to a sufficient depth for commercial oil generation. Therefore, further exploration efforts in deeper parts of the Shabwah depression, particularly in the area around well Misah-01, are recommended.