Study On AVO Analysis And Waveform Correction Of Thin Interlayer Reflections

With the increasing complexity of exploration targets,the lithologic reservoir gradually become an important part of China's proven reserves of oil and gas,such as thin interlayers.The thin interlayer has small thickness and its reservoir and non-reservoir interbedded seriously.Due to limitation of thickness,effective reflected waves interfere with multiples and converted waves,as a result,the seismic reflection characteristic become complex and make it difficult to seismic data processing and interpretation.Meanwhile,the practical data used to AVO analysis have problems in waveform consistency between near traces and far traces,which increases difficulties in AVO analysis of thin interlayers.So it is very necessary for identifying thin interlayers to study its seismic reflection characteristic and waveform correction method.This paper firstly started from the academic analysis of thin interlayers' seismic reflection characteristic,combined with the impact on seismic reflection of interference and tuning,and derived the expression of frequency characteristic with regard to thin interlayers' seismic reflection.At the meantime,the impact on frequency characteristic of viscosity has been analyzed.Then,the paper established different thin interlayer models about thickness,velocity,density and interlayer combination relation,and then carried out forward modeling with reflectivity method.The main factors that affect the normal seismic reflection characteristics and the influence of the thin interlayer's structure on the AVO response characteristics have been investigated.Based on the simple model,the typical thin interlayer models were established according to the actual geological situation.Then by using wave equation forward modeling,the numerical simulation of the model was carried out,and the prestack migration of the forward data was processed.According to the same research ideas,the seismic reflection characteristics of the typical thin interlayers were analyzed,in order to provide the basis for the identification of thin interlayers.Meanwhile,we studied the waveform correction method for AVO analysis.Based on the analysis of the causes of waveform distortion,the correction method was presented.Firstly,choose the standard trace,and quantify the stretching factor in the frequency domain.Design the stretching correction filter,and then apply it to the actual seismic data.When the seismic traces approach the standard trace,based on the difference of the frequency band between the traces,the variation of the amplitude and frequency of the reflected wave along with offset is effectively preserved under the condition of thin interlayers.Through the model data and actual data processing,it could be found that the seismic traces after correction have more continuous events,and waveform between near traces and far traces tend to be consistent.It is beneficial to the extraction of amplitude value,and improves the accuracy of AVO analysis,which is of great significance for the interpretation of thin interlayer reservoirs.