No consensus has been reached on the origin and source of natural gas in the Upper Paleozoic of Yimeng Uplift

Ordos Basin.Based on a comprehensive analysis of carbon isotope and light hydrocarbon

the δ

13

C

2

values are gene-rally more than -25.4‰

alkane carbon isotope values change in normal order and the relative content of methylcyclohexane is more than 50%

which show that natural gas is coal-derived gas.The Upper Paleozoic source rocks in Yimeng Uplift are dominated by coals.In Shiguhao area

the thickness of coalbeds ranges from 6 to 10 m.The source rocks with a vitrinite reflectance from 0.8% to 1.2% reached the major stage of hydrocarbon generation.So the local source rocks have an important contribution to near-source gas accumulation.Average methane content of Yimeng Uplift is 94.5%

which is higher than that of Shilijiahan area (91.2%); δ

13

C value was alos significantly heavier than that of Shilijiah area with the difference value of 3‰.It is believed that component differentiation and carbon isotope fractionation occurred in natural gas migration process.So some natural gas in the Upper Paleozoic of Yimeng Uplift may come from the south of Boerjianghaizi fault.