Organic geochemistry of the Early Cretaceous shales, Saar Formation in the East Shabwah oil fields, onshore Masila Basin of eastern Yemen

Abstract

The early Cretaceous Saar Formation includes potential petroleum-bearing source rocks in the onshore Masila Basin, eastern Yemen. The organic matter input, depositional environment conditions and petroleum generation potential from the Saar Formation shales were investigated using geochemical and organic petrological methods.The shales of the Saar Formation contain total organic carbon of 0.5–3.5 wt percent. The geochemical analysis of the organic matter indicated that these shales have fair to very good hydrocarbon source potential. The kerogen of the organic matter is dominated by Type II/III and Type III, referring to both oil- and gas-prone source rocks. The biomarker and bulk carbon isotope analyses of the organic matter suggested that the kerogens were constituted from a combination of marine and high land plant organic matter, and were preserved under suboxic depositional conditions.The geochemical and petrographic analyses of the shales (e.g., vitrinite reflectance (VRo), pyrolysis Tmax and biomarker maturity ratios) lead to the conclusion that the shales are generally immature to very early mature, particularly in shallower locations where the thermal alteration level of the organic matter is not strong enough to generate petroleum. Therefore, this work suggests that the mature source shale intervals of the Saar Formation existed in the deeper parts of the basin could reach a good maturity level that can produce potential hydrocarbons. Prediction of the potential migration pathways for hydrocarbons produced by deep shales could significantly aid in the future of petroleum exploration in the Masila Basin of Eastern Yemen.