Inversion of tight oil origin by geochemical characteristics: a case study of central Northern Shaanxi Slope, Ordos Basin

Hengshan area is located in the middle of the Northern Shaanxi Slope of the Ordos Basin. Due to the low degree of exploration and weak basic understanding, the origin of tight oil in the study area is not clear, which seriously restricts further exploration deployment. Based on this, this study analyzed the geochemical characteristics of tight oil in Yanchang Formation by chemometrics, then inversed its origin. The results show that the Chang 6 tight oil belongs to the mature stage without biodegradation, in which parent source was formed in a low salinity sedimentary environment. The source of organic matter was mainly from planktonic aquatic organisms and higher plants. Through chemometrics analysis, it is considered that it has a good affinity with the Chang 7 source rocks at the edge of the basin, while the difference with other samples mainly lies in maturity; the content of light components and C30DH/C30H parameters further indicates that the Chang 6 tight oil was generated from Chang 7 source rock at the edge of the basin and experienced a certain scale of lateral migration. Based on the above analysis, the origin of tight oil can be effectively inversed by using the geochemical characteristics of rock extracts in areas with unclear source rocks, which makes up for the blank in the field of tight oil exploration, and is of great significance for subsequent exploration.