SEDIMENTARY SYSTEM ANALYSIS OF FAN DELTA FOR THE SECOND MEMBER OF SHAHEJIE FORMATION AT THE BONAN SAG

According to the theories of sequence stratigraphy and the genetic facies study of well cores,and through a careful stratigraphic analysis of the second member of the Shahejie Formation,the fan delta depositional system and the main characteristics of reservoir rocks were analyzed and discussed.The study indicates that the stratigraphy at inner Bonan Sag is well developed,while the basal sands were generally absent in the raised edge due to the lack of supply source.The fan delta is the main depositional system,representing depositional background of shallow lakes.In the western and northern parts of the sag,small-scale near-shore subaqueous fan depositional systems were developed.The reservoir rocks are mainly siltstone,sandstone and pebbly sandstone in the fan-delta front edge,and the properties of reservoir in the southeast are closely related to oil and gas accumulation.