Abstract: Aiming at the problem of unclear understanding of the reservoir-forming mechanism and exploration potential of heavy oil reservoirs in the Ruman sag of the Melut Basin in South Sudan, the reservoir-forming mechanism of heavy oil reservoirs in the eastern slope of the Ruman sag was studied by using research methods such as source rock basin modeling and reservoir analysis, and the exploration potential of heavy oil in this area was analyzed. The results show that the primary reservoirs of the Yabus Formation, Gayger Formation and bedrock reservoirs in the eastern slope of the Ruman sag were destroyed due to the tectonic movement during the sedimentary period of the Lau Formation, and have become secondary residual heavy oil reservoirs, thus they have very limited exploration potential. The oil reservoir in the Jimidi Formation is a secondary heavy oil reservoir with late accumulation and favorable exploration area of about 21 km². The oil reservoir in the Galhak Formation belongs to a primary heavy oil reservoir with late accumulation and favorable exploration area of about 105 km². They both have larger exploration potential. This study can provide some reference and guidance for the next oil and gas exploration in the study area.

Key words: heavy oil, accumulation process, exploration potential, Oil source analysis, Accumulation process, Ruman sag, Melut Basin