Quantification of Mixed Oil Derived from Multiple Source Rocks: a Typical Case Study of the Cainan Oil filed in the East Junggar Basin, Northwest China

The crude oil in the Cainan field is a mixture of hydrocarbons of Permian, Triassic and Jurassic source rocks. Artificial mixing of three typical Permian, Triassic and Jurassic oils in the laboratory indicates that the whole-oil carbon isotope ratio δ13 C of the artificially mixed oil samples changes linearly with the mixing proportions, but the Pr/Ph.ratio, (β-carotane/n-C25 ratio, and various biomarker ratios in the mixture change non-linearly. The ternary plate created by the artificial mixing of the three typical oils shows that the average contribution of the Jurassic source rocks is 65% whereas those of the Triassic and Permian source rocks are around 15% and 20%, respectively. In summary, based on the whole-oil stable carbon isotope ratios and biomarker parameters it can be concluded that the Jurassic source makes a contribution of 55%~70%, while the Triassic and Permian sources each contribute by 10%~30%.