Seismic Recognition Studies On Subtle Traps Of Dainan Formation In Western Fault Zone Of Southern Gaoyou Sag

Based on the complex difficulties and conditions such as small subtle traps,different reservoir types and sand body which was changed fast laterally,seismic recognition on subtle traps was carried out,which included geological analysis and geophysical techniques.Through the above study,the following four achievements have been obtained.Identification model on channel sand body and sand-grabel fan reservoir have been established.The characteristics of seismic response to the channel sand body were concave-down,short event,lenticular-shape,middle-high amplitude,while the characteristics of seismic response to the sand-grabel fans were short,mound-shaped event in distal fan,with interfaced and weak reflections in the interior fan.The nearshore subaqueous fans in research zones were classified into four types including lenticular-shaped,wedged,tarsoned,flaged,faulted slope.The paper discussed the types of subtle traps.Analysis showed that the main types in research zones were fault-lithologic,nearshore subaqueous fans,sandstone updip wedge_out,Stratigraphic Overlapped and lenticular-shape.Through the analysis of characteristics of different lithology,different seismic recognition techniques have been formed.Analysis showed that the key techniques in fault-lithologic traps were spectral decomposition,seismic inversion and seismic facies;the key techniques in nearshore subaqueous fans were multi-attribute clustering,seismic forward modeling and three-dimensional visualization;the key techniques in sandstone updip wedge_out traps were trend analysis with intersection,seismic forward modeling and seismic inversion.