The Research Of Sedimentary Microfacies Of Shahejie Formation In The Lixian Slope,Raoyang Sag

The “lowermost sandstone” of the bottom part of lower sub-member is one of those important oil-bearing formations in the First Member of Shahejie Formation in Lixian Slope,Raoyang Sag.Previous researchers have done many work to study the types and distribution of sedimentary facies,while less attention were focused on the sedimentary microfacies characteristics.Therefore,it is essential to do more detailed research to the microfacies and distribution features of the individual lowermost sand bodies,in order to explore the lithological reservoirs in Lixian Slope.Guided by the principles of sequence stratigraphy,the sedimentary characteristics of the lowermost sandstones,which include the provenance direction,microfacies types,the distribution of the sand bodies and the depositional model,had been utilized on the basis of core data,test data and wireline-log data.Three main provenance directions were identified,the sediments come from the west,the southwest and the north.The main source of sediments are the western and southwestern drainage systems.It is also revealed that braided river delta systems are well developed in the study area,and the major sub-facies are braided delta front and shallow lake,which could be further divided into several microfacies such as subaqueous distributary channel,estuary dam,sheet sand,beach and dam,and etc.Influenced by the lacustrine transgression,the braided delta front shows a characteristic of landward regression,resulting in the westward retreat of the sand bodies and the expansion of the lake.Based on the results above,a study to the physical properties of different types of sandstones had been conducted.Favorable reservoir zones were figured out,and a series of predictions had been made to the lithological traps developing area,with the combine of regional structural features.