Study on the Sedimentary Facies of Chang 8 Oil Group of Yanchang Formation in Jiyuan Area of Ordos Basin

The Chang-8 oil group of Yanchang Formation was an important petroleum reservoir in Jiyuan area, because of the imperfect study on sedimentary facies, till now, sand-body distribution was unclear. Based on the tectonic and sedimentary evolution of Ordos Basin, rock types, sandstone structure, sedimentary tectonics, paleontological fossil, geochemical features were analyzed.The result shows that there exist a set of meandering river delta sedimentary systems in the environment of semi-arid, Semi-humid and fresh-light salt water. This meandering river delta sedimentary systems include delta plain and delta front, microfacies of the delta plain is consisted of distributary channel, above water natural levee, above water overbank that is mainly on swamp, and microfacies of the delta front includes subaqueous distributary channel, subaqueous natural levee, channel mouth bar(distal bar), frontal sheet sand and so on. According to geochemical principle, the boundary between meandering delta plain and front sub-facies is confirmed.