Study on sedimentary facies of Chang 4+5 oil unit in Triassic Yanchang formation in Huachi area of Ordos Basin

This paper studies the sedimentary characteristics through analysis of lithology,logs and sedimentary microfacies based on outcrop,core and well logging data of the study area. It is thought that the Chang 4+5 oil unit of Yanchang formation in Huachi area mainly comprises delta and lacustrine depositional systems which can be further divided into many subfacies. This delta depositional system includes not only NE-trending meandering river delta sedimentation but also SW-trending braided river delta sedimentation. This study deepens the understanding of reservoir characteristics and distribution,hydrocarbon enrichment regularity,and reservoir-forming mechanism in traps,and provides certain guidance for petroleum exploration in this area.