Origin of Chang 10 oil reservoir in Northern Shaanxi region of Ordos Basin

The Chang 10 oil reservoir was discovered through the exploration in the Zhidan region of Ordos Basin, where the crude shows a density of 0. 8152 g /cm3 and a main peak at nC15 in the whole hydrocarbon chromatogram. The crude consists mainly of light hydrocarbons, which include abundant naphthenic hydrocarbons and low content of aromatic hydrocarbons, and has an equilibrial ratio of Pr / Ph, varing from 1. 21 to 1. 45, and - 31. 78‰ of δ13CPDB for the whole crude. Its terpane distribution is characterized by relatively abundant rearranged hopanes, low content of gammacerane, and high ratios of Ts /Tm (5. 54 - 7. 26), C30* /C30 hopane (0. 67 - 0. 72), and C29Ts / C30 hopane (0. 38 - 0. 52). The steranes in the crude mainly consist of rearranged steranes, and show abundant αβ and βα isomers, while ααα-20R sterane isomers display an asymmetricVtype distribution pattern, representing a typical lacustrine-derived oil. The oil-oil and oil-source correlations indicate that the crude oil of Chang 10 oil reservoir is originated from the excellent hydrocarbon source rocks of the Chang 7 member in the center of the basin, and migrated vertically into the Chang 10 oil layer, and then accumulated laterally. Therefore, it can be predicted that the Chang 9 and Chang 10 oil reservoirs in the Ordos Basin have favorable reservoir-forming conditions and great potential for exploration.