Based on the appraisal of source rocks in the Yitong Basin

we studied the geochemical characteristics and origin of natural gas in that basin.Using the Basinflow software

and simulated the directions of gas migration to recognize the favorable accumulation zones.The results show that there are three sets of source rocks in the Yitong Basin

including the Shuangyang

Sheling and Yongji formations

among which the Shuangyang Formation source rocks are the highest in the organic matter abundance.The types of organic matter are mainly TypeⅡ

1

and Ⅱ

2

partly Type Ⅲ andⅠ.The natural gas

with its maturity below 1.3%

is mainly composed of wet gas and is classified as associated gas.The gases in the Yitong Basin are mostly of oil-type and partly of mixed origins.The kerogens of the source rocks are mainly of TypeⅡ

1

and Ⅱ

2

.The simulation results of gas migration and accumulation show that

the Wanchang structural belt and the hanging wall of No.2 fault in the Wuxing structu-ral belt of the Yitong Basin are the most favorable areas for gas accumulation and are characterized by contribution from two sources.