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Geochemical Characterizations of Source and Depositional Environment of Hydrocarbons in the Lake Albert Rift Basin

Despite the upsurge in hydrocarbon exploration in the Lake Albert Rift Basin (LARB) over the past three decades, systematic characterization of hydrocarbon compositions remains lacking, leading to uncertainties in source rock and oil generation determination. We characterized crude oil compositions and oil sand samples in the northern and southern subbasins of LARB. The relative abundance of normal and branched linear alkanes, hopanes, steranes, and aromatic hydrocarbon suggest that northern and southern hydrocarbons were deposited in anoxic to suboxic lacustrine environments and share similar biological source compositions (i.e., a mixture of plants and aquatic algae and bacteria). Relative to southern samples, northern samples show more negative δ13C values for oils, saturates and aromatics, indicating longer migration paths, and exhibit higher MPI‐1, DNR‐1 and 4‐/1‐MDBT ratios, indicating higher maturity. Between the two possible sets of source rocks (upper Miocene and Jurassic strata), the positive δ13C values of saturated hydrocarbons (average = –20.5‰) suggest that the upper Miocene lacustrine shale is the most likely candidate. Oleanane index (<5% in our samples) does not exclude either source rock possibility, and C28/C29 regular sterane (average = 0.63) may be biased by high terrestrial inputs in a lacustrine setting. Together, our data show that northern and southern oils originate from the same source rocks but different oil kitchens. Given the similar geochemical characteristics of southern and northern oils, previous exploration successes in the northern subbasin likely suggest similar potential in the southern sector, while other elements influencing exploration success must be also evaluated.