Petroleum generation modeling of the organic-rich shales of Late Jurassic – Early Cretaceous succession from Mintaq-01 well in the Wadi Hajar sub-basin, Yemen

Abstract

Late Jurassic – Early Cretaceous shales of the Naifa, Safer, and Madbi formations were studied to evaluate source rock characterization. The results of the source rock were then incorporated into basin modeling to understand the timing of hydrocarbon (HC) generation and expulsion. The Late Jurassic – Early Cretaceous shales have low to high organic matter, with total organic carbon (TOC) values in the range of 0.50%–28.01%, indicating fair to excellent source rock potential. Main oil and gas are anticipated to be generated from the Naifa, Safer, and Lam shale samples with types I and (or) II and types II–III kerogens. In contrast, the Meem samples are dominated by type III kerogen (hydrogen index, HI < 200 mg HC / g TOC), and are thus considered to be gas prone. The Late Jurassic – Early Cretaceous shale samples have temperatures of maximum pyrolysis yield (Tmax) in the range of 337–515 °C, consistent with immature to post-mature stages. The Tmaxdata also indicate that the Safer and Madbi shale samples have sufficient thermal maturity, i.e., peak–mature oil and gas window. The basin models indicate that the Naifa Formation is early–mature, and the onset oil generation began during the Early Miocene. The models also indicate that the main phase of oil generation in the Safer source rock began during the Late Eocene. In contrast, the Madbi source rock units had passed the peak oil generation window, and the oil was converted to gas during the Late Cretaceous to Late Eocene. The modeled HC expulsion history reveals that most oils are contributed by both Madbi units, with significant amounts of gas originating from the Meem unit.