Geochemistry and Genesis of Crude Oils of the Xifeng Oilfield in the Ordos Basin

Crude oil samples of the Xifeng oilfield in the Ordos basin were collected systematically and analyzed by means of high-resolution GC-MS and IRMS. In this paper, biomarkers and carbon isotopic compositions in crude oils were studied, and the oil/source correlation and their genesis were discussed. The data indicate that the studied oils are of the same genetic type. The oil-forming matrixes are algae and higher plants, especially with an important contribution of higher plants to the formation. The crude oils were formed under weak reducing and fresh water environments. The crude oils are mature. The geochemical characteristics of crude oils are closely correlated to those of the Upper Triassic Chang-7 subsection, reflecting that crude oils were mainly originated from the Chang-7 oil bed group.