Hydrocarbon accumulation significance of Chang 91 high-quality lacustrine source rocks of Yanchang Formation, Ordos Basin

The comprehensive identification by logging and organic geochemistry reveals that the Chang 91 high-quality source rock of black lacustrine mud shale mainly develops in the south of Zhidan region. The source rock has both strong hydrocarbon-generating capability and strong hydrocarbon-expulsion power. According to the characteristics of high C30-rearranged hopane abundance and extremely low C30 hopane abundance of the Chang 91 source rock, in combination with other geochemical parameters in oil-source correlation, it has been found that Chang 8–Chang 9 reservoir oil shows a close relationship with Chang 91 source rock in the south of Zhidan region and there is a poor correlation between Chang 91 reservoir oil and Chang 91 source rock in other areas. Chang 91 source bed is an important zonal oil source rock and it plays an important role in the formation of Chang 8–Chang 9 reservoir in Yanchang Formation in the south of Zhidan region.