The occurrence of ultra-deep heavy oils in the Tabei Uplift of the Tarim Basin, NW China

► Heavy oils are extensively distributed in deep hot reservoirs in northern Tarim Basin. ► Heavy oils are mainly derived from the Middle-Upper Ordovician source rocks. ► Heavy oils were formed by biodegradation during late Permian. ► Late charge is mainly from the same phase of generation. ► Low degree of thermal cracking is due to decreased heat flow and short heating time.