Abstract：Yanchang formation is the main oil-bearing segments of Jiyuan area, Ordos basin. The composition, morphology, spatial distribution and homogenization temperature of its fluid inclusion were systematic analyzed.Meanwhile, the period of hydrocarbon charge and reservoir forming was defined based on the basin burial history, hydrocarbon generation and paleotemperature evolution. The results show that there exist two types of fluid inclusions. One type has small single-size and low-abundance which is distributed in the inner margin area of the secondary enlargement of the quartz and calcite, the homogenization temperature ranges 63 ~ 87 ℃ and the average temperature is 80 ℃. The other type has large single-size and high-abundance which is distributed in the outer margin area of the secondary enlargement of the quartz and fracture-filling calcite, the homogenization temperature ranges 115 ~ 150 ℃ and the average temperature is 127 ℃. Through synthesis analysis of Yanchang formation, the first time of hydrocarbon migration and reservoir forming was taken place in the early period of Early Cretaceous ( 145 Ma ±) and with small range of hydrocarbon filling and reservoir forming. In the late period of Early Cretaceous ( 110 Ma ±) , the main source rock ( Chang 7) began to enter the peak hydrocarbon-generating stage with massive hydrocarbon expulsion and the large range of reservoir forming. It is the main accumulation period of Yanchang formation in Jiyuan area.

Keyword：fluid inclusion;homogenization temperature;hydrocarbon charge and reservoir forming period;Yanchang formation;Jiyuan oilfiled;