The Study On Sedimentary Characterization Of Shahezi Formation In Xujiaweizi Fault Depression

Based on the predecessors' research of Xujiaweizi Depression,the author divided the sequence stratigraphic framework of 83 wells and deeply studied the sequence stratigraphy group strata in Shahezi,combined with the logging and seismic data.According to the theoretical basis of application of sequence stratigraphy and sedimentary petrology,and depositional base-level cycle characteristics,the Shahezi group has been divided into five three-grade sequences—SQ1,SQ2,SQ3,SQ4,SQ5.According to 31 coring Wells of core description,the sedimentary characteristics,such as color,lithology,structural features,sedimentary structure,and paleontology analysis,has been analyzed,the same as the subgroups sign of sedimentary facies characteristics of Shahezi group,sedimentary system and sedimentary facies distribution characteristics.We concluded that the study area developed five types of sedimentary facies,included fan-delta facies,braided river delta facies,lake facies,nearshore subaqueous fan facies,Sublacustrine fan facies,among them is lake facies,braided river delta facies,fan-delta facies,sublacustrine fan facies developed in some areas.Xuxi trend controlled fan delta deposition,sediments grain size is coarse,and seismic reflection configuration is chaotic;Xudong gentle slope controlled braided river deposition,sediments grain size is also coarse,and the depositional scale is big.Controlled by basket shape rift,the settlement center located in the western middle of depression is mainly fan delta facies;the depositional center located in the middle or western middle of depression is mainly lake facies,and part of sublacustrine fan.The sediments grain size is small.The horizontal characters of sedimentary facies have been drawn from the control functions caused by source direction,pathway within the three-grade sequence and the information such as single well facies,section facies,seismic facies,seismic attributes and several kinds of contour.We drew the plan of sedimentary facies in three-grade sequence unit,which demonstrated the differences between different kinds of three-grade sequences in forms,distributions and evolutions.