Upper Jurassic Source Rock Evaluation and Thermal Maturity Evolution of the NW Sab’Atayn Basin, Yemen

Abstract

Of Yemen’s Mesozoic basins, the Sab’atayn Basin offers the most significant potential for oil and gas exploration. The key consideration in the evaluation of source rocks to hydrocarbon exploration is the quantity and nature of the organic materials in sedimentations. Using organic geochemistry and total organic carbon content, organic-rich sediments from the Meem (Lower) and Lam (Upper) members from four wells in the NW Sab’atayn Basin were evaluated. The information gained reveals that the Meem source rocks have a total organic carbon content (TOC) value between 0.2–1.68 wt%, therefore suggests fair to very good source rocks. Only two samples in the Kamaran-01 well had values greater than 3 wt%, compared to the Lam source rocks’ values, which range from 0.2 to 3.81 wt%, which suggest excellent source rocks. The majority of the samples are made up of reworked organic debris, with no possibility for interesting source rocks, according to the Rock-Eval pyrolysis data. The majority of the Meem and Lam source rocks samples under study have Tmax values below 440 °C, placing them in the immature to marginally mature and on the main periphery of main phases of hydrocarbon formation. Based on the results of the Meem source rocks’ generative potential (GP), it may be inferred that non-generative rocks status of Meem source rocks due to GP values less than 2 mg HC/gm rock. Additionally, if the burial depth is sufficient to generate the necessary temperature and pressure, source rocks with extraordinarily high GP values of more than 10 mg Hc/g rock may serve as an efficient source rock for the Dahamr Ali-01 well. On the other hand Lam source rock is classified as moderate source rocks. Non-generative potential has been reported from Lam source rock in Himyar-01 well where the GP is less than 1 mg HC/g rock. The cross-plots of pyrolysis characteristics, such as HI versus Tmax (modified van Krevelen diagram) and TOC vs S2, which are most likely the result of deposition of more terrigenous type III organic materials derived from terrestrial in the study area, can be used to determine the kerogen type for Lam and Meem source units. The analysis of Meem source rocks demonstrated that they are typically plotted in the mature zone; however samples of Lam source rocks proved that they have been still immature, merely marginally mature in the Dahamr Ali-01 and Saba-01 wells.