The discovery and significance of the crude oils derived from Triassic source rocks in the Junggar Basin

It is the first discovery of the crude oils derived from Triassic source rocks in the Junggar Basin. The geochemical characteristics of the oils differ from those of the oils derived from Carboniferous, Permian and Jurassic source rocks in the basin. The Triassic derived oils are mature crude oil with a normal density and viscosity, and are dominated by over 80%of saturated hydrocarbons. The oils are rich in isoprenoids, with Pr/Ph ratios around 1.0, and are isotopically light, with δ13C values generally around -31‰, are characteristically rich in diasteranes, Ts, C29Ts, C30 diahopane, and have a low content of β carotane and gammacerane. These biomarker features of the oils are similar to those of Triassic extracts, and are different from those of Permian and Jurassic extracts, which indicates the oils are derived from Triassic source rocks. The comparison of TOC content and the genetic potential of Triassic source rock with those of the Permian and Jurassic source rocks indicates that Triassic is a set of good and important source rock, with high hydrocarbon generating potential. The discovery of Triassic derived oils has an important significance for petroleum exploration in the Junggar basin.