Oil and source rock correlation of lower assemblage of Yanchang Formation in Wuqi and Dingbian areas, Ordos Basin

The geochemical correlation of source rock and crude oil from the lower assemblage (Chang7, 9, 10, respectively) of the Yanchang Formation has indicated that, the carbon preference index (CPI) of the Chang7 source rock is 1.2, and that of the Chang9 and Chang10 source rocks is 1.09. The odd-even predominance (OEP) of carbon disappears in the Chang7, 9, 10 source rocks. In the Chang7 source rock, the relative content of Ts is higher than that of Tm, while in the Chang9 and Chang10 source rocks, the relative content of Ts is lower than that of Tm, indicating for higher maturity of the Chang7 source rock. The C₂₇, C₂₈, C₂₉ ααα20R regular steranes of the Chang7 source rock distribute in "V" and "L" shapes, and those of the Chang9 source rock in nearly "V" and anti-"L" shapes, and those of the Chang10 source rock in anti-"L" shape. Crude oil in the Chang8 strata mainly originated from the Chang7 source rock in the west of the study area, and from both the Chang7 and Chang9 source rocks in the east and south. Crude oil in the Chang9 strata mainly originated from the Chang10 source rock in the west of the study area, and from both the Chang9 and Chang10 source rocks in the east and south. Crude oil in the Chang10 strata originated from both the Chang10 and Chang9 source rocks in the south.