Petroleum geology and hydrocarbon prospectivity of the Eyl Sub-Basin, Southeastern extension of the Nogal Rift, North Central Somalia

The Nogal Basin of northern Somalia remains one of East Africa's least-tested rift systems. This study evaluates the petroleum geology of the Eyl sub-basin, the onshore southeastern continuation of the Nogal Rift, by integrating ∼2279 line-km of 2D seismic data with regional wells, aeromagnetic data, soil-gas microseep measurements, and 1D/2D petroleum system models. Seismic profiles image WNW–ESE-trending half-grabens with syn-depositional thickening against basin-bounding faults. These contain Upper Cretaceous (Jesomma–Gumburo) and locally developed Upper Jurassic successions, overlain by Paleogene platform carbonates (Auradu) and Taleh evaporites with local Oligo–Miocene syn-rift clastics. Depth structure mapping indicates up to 4 km of cumulative section in the sub-basin center, consistent with polyphase extension in the Late Jurassic, Late Cretaceous, and Oligo–Miocene. Basin modeling calibrated to Garad Mare-1 vitrinite reflectance suggests that Upper Jurassic Uarandab (Daghani/Gahodleh equivalents) marine shales are presently within the early to main oil window in parts of the sub-basin, with transformation ratio locally ≥50% in areas of maximum burial. Soil-gas anomalies (characterized by low C₂/C₃ ratios) align with mapped closures, supporting an active oil-prone system. Prospective plays include tilted fault blocks and rollovers in the Jesomma–Gumburo and Adigrat intervals, as well as Upper Jurassic carbonates, sealed by intraformational shales, Taleh evaporites, and tight Auradu carbonates. Principal risks include fault-seal integrity under Oligo–Miocene reactivation and spatial variability of Jurassic source facies. We recommend acquiring modern, tightly spaced 2D/targeted 3D seismic, alongside detailed fault-seal analysis, to refine prospect evaluation.