Seismic Sequence And Seismic Facies In The Yanchang Formation Of Ordos Basin

Ordos Basin is one of the major oil and gas basin in China,the structural influence by its eastern the Pacific tectonic domain and its southwest the Tethys-Himalayas tectonic domain,that it is a cyclicity craton superimposed basins in our country.In this paper the Yanchang Formation across the Gansu and Shaanxi provinces mostly located in south-central Ordos Basin,the research scope west to HuanXian,north to DingBian,east to FuXian,south to ZhengNing,including main area of Chang7and Chang9member of the basin.Because of the seismic exploration technology progress in loess tableland and the fast development of compacted sandstone of Yanchang Formation,this paper aims to use the new seismic data to deepening understanding the Seismic Stratigraphy of Yanchang Formation and the Seismic Phase and lake basin evolution,so as to improve the development of oil an gas exploration results. It divide the Yanchang Formation with three seismic stratigraphy after analyses the seismic unconformity phenomenon of the top and bottom and internal of Yanchang Formation by more than402D seismic lines and200logging data.In the seicmic section find a lot of Foreset Reflections from northeast,southwestand southeast and so on different direction,according to established the diachronous phenomenon of drilling layered in the foreset area,determine its diachronism.The paper discusses the ancient water depth in the foreset reflection area by the thickness between topset and bottomset of the Foreset Reflections in the seismic section,and find the ancient water depth in Chang6stage close to200m.The authoer detailed analysis the seismic response characteristics of the mudstone in Chang7member and the delta front sandstone in Chang6member by observerd the section classification,the forward modeling and the inversion.Use the logging curve making the mudstone thickness graphs of three lake lake flooding period,and find the sedimentary center gradually to the southwest directiong migration,and the delta filling of the basin is gradually moved from north to south after Chang6stage.Use the logging GR after standardlization to statistical analysis the mudstone percentage content and sandstone thickness to made the sandston thickness plan,which reflect the GR average in the northeast of the sandstone material sources is higher than the southwest of the sandstone material sources about20API,this differenc reflect the two material sources have differences radioactive potassium feldspar content.The quartz sandstone of the southwest material sources mainly provided by Qinling Qilian orogenic,and the arkose of northeast material sources mainly provided by the craton basement.