Sequence stratigraphy study on Sha-4 formation of Sheng-25 well area in Damintun sag

Sha-4 formation in Damintun sag is the sedimentary product of fault depression-in deep fault depression period,with the characteristics of big thickness,better oil source condition and big exploration potential.Through well logging,mud logging and seismic data analysis,isochronous stratigraphic framework of Sha-4 formation has been established.The framework made a detailed description and subdivision of the internal structure,sequence boundaries and system domain,and identified out sequence interfaces SB1and SB2.In Sha-4 formation,the sequence interior can be divided into low stand system tract and transgressive system tract.Parasequence set mainly developed aggradation type and retrogradation type.Through the establishment of se-quence stratigraphic framework including sedimentary facies and reservoir distribution,Sha-4formation was found to be widely developed multi-time,multi-level reservoirs,which pointed out a favorable direction for deep fault depression in the study area.