Simulation Analysis Of Multiples And Ghosts Time-distance Based On Marine Seismic Data

Currently,the study on the active fault in the land area has been relatively mature,while there is still a lack of detection and research for active fault in the sea area.Marine exploration,which different from land area,has a prominent problem due to the existence of strong reflecting interfaces such as water surface and seafloor in the sea,thus the recording is often accompanied by interference of multiples on seafloor reflections which has always plagued the data and seriously affects the quality of records.For a long time the marine geophysical research has been focus on how to distinguish whether the reflected signals in the marine seismic record is a multiple wave from the shallow reflection interface or a primary wave at the deep reflection interface,to avoid the misjudging due to the interpretation of the seismic data.Inclined interfaces,that often exist in the offshore and deep water area of complex structures,can be another problem due to their specific multiple waves propagation characteristics,and it is difficult to eliminate this interference by traditional multiples suppression methods,which based on the horizontal interface assumption,and makes the signal-to-noise ratio of seismic records reduction.In addition,because of the characteristics of marine seismic exploration,the source exciting in the water and the geophone receiving in the water,the ghost wave accompanying the reflected wave propagation usually exists in the record,and the moveout between the reflected wave and it's ghost wave is short,which brings difficulties to distinguish between effective waves and noise,and reduces the quality of seismic records.Based on these,effectively simulating the time-distance characteristics of the multiples waves and their ghost waves,especially the multiple waves and their ghost wave time caused by the inclined interface are the premise of multiple wave recognition and suppression.In this paper,according to combine the sea area seismic data and its acquisition method,based on the multiples time-distance analysis of inclined interface,picking the arrival time and estimate the speed of seismic wave and interface parameter estimation for actual records of complex structures in shallow and deep water,and establish the simplify multi-layered medium model with inclined interface,to perform time-distance forward modeling based on the model and fit the strong reflection event in the record.We simulate the surface related multiples and the internal multiples under the model,meanwhile according to the reflected wave propagation path,calculate the root mean square velocity of the reflected wave in different paths,and simulate the multiple wave time-distance curves of different interfaces,different orders and different categories.Comparing the simulation results of the multiple waves time-distance forward and actual records,the results are consistent with the positions of the reflected waves in the actual record.The forward modeling can help to distinguish the causes of reflected waves,summarize the multiplewave time-distance characteristics from different interfaces(including inclined interfaces),and analyze the relationship between the characteristics of multiple waves and primary waves,in particular,the internal multiples that are difficult to identify due to inconspicuous periodicity and the multiples of the inclined interface which present the phenomenon that the vertex of the time-distance curve are shifted at.Therefore,it is beneficial to the identification of effective waves and can improve the observation and interpretation ability of seismic data.Secondly,based on the multiple waves forward modeling,according to the multilayer medium model and the actual acquisition parameters,the time-distance forward modeling of ghost waves is carried out.Based on the analysis of ghost wave timedistance,we analyze the travel time difference characteristics between reflected waves and their accompanying ghost waves.The differences of the different orders ghost wave and reflected wave travel time difference characteristics are summarized and the symmetry of the travel time difference between inclined interface and horizontal interface of ghost waves and reflected waves is analyzed.And then,by changing the parameters of the depth of the source and the geophone,the distraction of the ghost wave event with the event of the reflected wave is simulated,and the influence of the ghost wave on the sea area record is further analyzed.In actual production,the source depth,geophone depth and observation system can be guided by ghost wave timedistance forward modeling simulated,thereby reducing the interference of ghost waves on seismic records,improving the signal-to-noise ratio of records,and convenient for subsequent processing and interpretation work.At last,on the basis of the forward model,according to extended the stratum to establish the observation system and obtain the time-distance information of the multishot data by forward modeling,take it converted into seismic information and artificially synthesized into a theoretical marine seismic record in the SEGY format.Using CGG seismic data processing software,the theoretical records are processed by conventional seismic data processing steps such as gather extraction,velocity spectrum analysis,normal moveout correction,and CMP horizontal stacking.The processing results are analyzed and interpreted to further understanding the characteristics of the time-distance,speeds and the resulting interface artifacts caused by multiple waves from different interfaces and deepen the understanding and summary of the multi-wave post-stack features in the seismic data of the sea and the correlation between multiple waves and interfaces.Under normal circumstances,there is a significant speed difference between the primary wave and the multiple wave in the adjacent time and using the velocity analysis and the dynamic correction can distinguish the primary wave from the multiple wave.Using the stacking profile results of theoretical seismic records,combined with the theoretical analysis of forward modeling,the periodicity of the horizontal interface and the relationship between the different inclinations of the inclined interface can be more intuitively resolved,and the causes of each interface in the stacking profile can be effectively analyzed.It provides a more intuitive analysis of the relationship between pseudo-depth section and interfaces,and provides a theoretical basis for the identification and prediction of multiple waves.In addition,this paper based on the multiples time-distance analysis,considering the source depth and the geophone depth,the two-dimensional time-distance inversion of the synthetic sea area theoretical shot records is carried out,and the normal depth,velocity and dip of the stratum are given.Comparing the model parameters,it is found that this inversion method has higher precision and can optimize the process of building a model based on actual seismic records.In summary,this study combines multiples and its ghost wave time-distance simulation with conventional seismic data processing to analyze the pre-stack and poststack features of multiple waves and their ghost waves in the seismic records of the sea area.The research results will be beneficial to the effective identification and prediction of multiple waves and their ghost waves in the sea area seismic record,improving the accuracy of seismic data observation,processing and interpretation in the sea area.Furthermore,it may provide some help for the research of activity tectonics in the sea area and has important practical significance for seismic exploration in the sea area.