Study On Seismic Response Characteristics And Prediction Method Of Thin Layer

In recent years,with the continuous deepening and increasing difficulty of oil and gas exploration and development,exploration targets have gradually entered the stage of subtle(lithological)oil and gas exploration and development,and thin layers have gradually become the focus and difficulty of people’s attention.Seismic attribute analysis technology is currently one of the effective methods for predicting thin reservoirs and plays an important role in oil and gas exploration and development.However,due to the fact that the seismic waves generated by adjacent thin interlayers interact and stack within the thin layer,the stacking effect is influenced by many factors such as the number of interlayers,sand mud ratio,spatial structure,etc.Therefore,it is difficult to predict the thin layer using conventional attribute thin layer quantitative description methods.Therefore,it is of great significance to summarize the impact of changes in parameters of thin interbeds on the vertical reflection characteristics of thin interbeds,and to find accurate and stable methods for qualitative prediction of thin sand bodies.On the basis of fully absorbing the research results of previous physicists on thin reservoirs,combined with the actual geological characteristics of the grape flower sand mudstone thin interbedded layer in the northern part of the Daqing Placanticline in the Songliao Basin,combined with the centroid frequency root mean square amplitude composite seismic attribute method,thin reservoir prediction research is carried out.Firstly,a thin interbedded model with multiple layers of sandstone and mudstone mixed and alternating sedimentation was established for forward modeling.Through attribute analysis,amplitude and frequency were selected as sensitive attribute parameters for the reservoir,providing a technical basis for qualitative identification and quantitative prediction of thickness of thin reservoirs in complex geological environments;At the same time,based on this,the actual river facies sand mudstone thin interbed model was analyzed and simulated,and it was found that the cumulative thickness change of the sand body has a certain variation relationship with the two sensitive attributes of amplitude and frequency,providing a basis for the subsequent use of amplitude and frequency composite seismic attributes to predict thin layers.Secondly,various geological models of thin interbeds were established,and convolutional forward modeling was used to simulate the seismic response of thin interbed models under different thicknesses,velocities,structures,and combination conditions.It was found that the seismic response characteristics of thin interbeds are not only related to factors such as thin layer thickness,number of interbeds,and sand mud ratio,but also to changes in the structure of thin interbeds,main frequency of incident wavelet,sampling rate,and other factors that can cause changes in reservoir reflection characteristics,This indicates that seismic wavelet with wide,high frequency,and high sampling rate is the key to improving the resolution ability of geological exploration.Finally,in order to reduce the thickness error caused by the nonlinear relationship between seismic attributes and thin layer thickness,a composite seismic attribute prediction method consisting of root mean square amplitude and centroid frequency was proposed.The stability and accuracy of the composite attribute prediction of thin layer thickness were confirmed through noise addition and low-frequency experiments compared with the other five attributes;At the same time,the established composite seismic attribute method was applied to the actual data of the thin interlayer of grape flower sand and mudstone,and compared with the standard cumulative thickness on the well.The results showed that the composite attribute had high accuracy in predicting the cumulative thickness of sand bodies,further confirming the reliability of the composite attribute of centroid frequency root mean square amplitude reservoir prediction and effectively solving the problem of thin sand body prediction,It plays an important guiding role in the exploration and development of thin sand reservoirs in the later stage.