Provenance Analysis of Benxi Formation in Yanchang Exploration Area of Ordos Basin

The source of detrital material is one of the important factors controlling the development and distribution of the Benxi Formation sandstone reservoir in the Yanchang exploration area. On the basis of previous research, this article conducted four methods for the source analysis of the Benxi Formation, including detrital zircon age, heavy mineral combination types, trace elements, and sandstone gravel size statistical analysis, on sand and mudstone samples from 37 wells in the Yanchang exploration area. The peak ages of 1912 Ma and 2425 Ma in the exploration area correspond to the northern edge of the North China Craton, while the peak ages of 435-447 Ma and 952-976 Ma in the remaining five wells correspond to the peak ages of the North Qinling Mountains. Based on this, the sources in the exploration area can be divided into two directions: north and south; In the analysis of heavy mineral combination types, the southwest region has a higher content of zircon and tourmaline, while the southeast region has a higher content of rutile. Therefore, the southern source can be further divided into two directions: southwest and southeast; Corresponding to the analysis results of heavy minerals, in the analysis of trace element zirconium niobium ratio, there are two directions of material sources in the southwest Longdong region and the southeast Yuxi region; Finally, by analyzing the distribution characteristics of sandstone gravel diameter on the plane, it is shown that there are sources from the southeast direction in the study area. Through comprehensive analysis, it can be concluded that the Benxi Formation in the Yanchang exploration area can be generally divided into three source areas: northeast, southwest, and southeast, indicating the erosion areas in the northern margin of the basin, the southern margin of the Qilian Mountains, and the eastern section of the North Qinling Mountains. Among them, the southeast source area is the thickest and closest to the Yanchang exploration area. This achievement has identified three directions of material sources and their influencing areas within the study area, which has important reference significance for predicting the distribution of sand bodies and dividing sedimentary facies in the Yanchang Benxi Formation gas field.