Objective The Yishan slope is an area of significant oil and gas−bearing potential within the Ordos Basin, the delineation of the oil and gas formation periods is of paramount importance in the revelation of the laws governing oil and gas storage, and in the provision of guidelines for exploration and development.

Methods The timing of oil and gas charging can be determined by measuring the homogeneous temperature of fluid inclusions in the Shanxi−Shihezi Formation in the Wuqi area of the Ordos Basin. This is combined with petrological characteristics and thermal evolution history research methods.

Results The microscopic observation results show that there are mainly two stages of fluid inclusions in the Shanxi−Shihezi Formation in the study area. The early inclusions are mainly distributed in the microcracks quartz particles and the enlarged edges of quartz, and the late inclusions are mainly distributed in the late cement. Through the implementation homogenization temperature test, the peak temperature distribution of early inclusions is 110~120℃, while the peak temperature distribution of late inclusions is 140~150℃.

Conclusions Combined with the analysis of the thermal evolution history and diagenesis, it can be concluded that there are two periods of oil and gas filling: the first period of oil and gas charging time is the Late Triassic—Early Jurassic (212~195 Ma), the reservoir is in the early diagenetic stage B. During this period, the thermal evolution of the coal−bearing stratum reaches the mature stage with dissolution and replacement being the predominant processes. The second period of oil and gas charging time, spanning the Late Jurassic to Early Cretaceous (155~130 Ma), coincides with the middle diagenetic stage A. In this stage, the diagenetic process is primarily dominated by the dissolution of calcareous cement, leading to an increase in secondary pores and the attainment of the highest thermal evolution, which marks the primary charging time.