Study on the Sedimentary Facies of Chang-7 Oil Group of Yanchang Formation in Fengdikeng-Hongde Area of Ordos Basin

The Chang-7 of Fengdikeng-Hongde Area was one of the important oil groups in Yanchang Formation of Ordos basin,but the study on sedimentary facies always keeped a low level. Based on the tectonic and sedimentary evolution of Ordos Basin,rock types,sandstone structure,sedimentary tectonics,paleontologic evidence and electrofacies of the Chang-7 oil group were studied in detail. The types and characteristics of sedimentary facies of Chang-7 oil group were analyzed concretely,and the sedimentary model were built. The result shows that there exist a set of meandering river delta and lacustrine sedimentary systems. The meandering river delta facies develops two subfacies as delta front and prodelta,and lacustrine facies develops shallow lake subfacies. Delta front develops five microfacies as subaqueous distributary channel,subaqueous natural levee,interdistributary bay,channel mouth bar and frontal sheet sand,among which the sand body is mainly packsand and siltstone.