Study Of Body Wave And Surface Wave Separation And Joint Inversion Based On Dispersion Characteristics

In land seismic exploration,surface waves mainly refer to Rayleigh waves and Love waves,which propagate along free surfaces and usually have the characteristics of low frequency,low velocity,strong amplitude and dispersion.At present,surface wave analysis has been widely used in engineering exploration.But in petroleum geophysical prospecting,we usually treat surface waves as interference waves and remove them.With the increasing application of surface wave exploration technology,surface wave records in petroleum exploration data have gradually been paid more attention to and used to invert near-surface velocities,and certain results have been achieved.In order to effectively use the surface waves in the petroleum seismic data,this paper firstly studies the dispersion characteristics of surface waves from the forward modeling of surface wave dispersion curves and extracts the dispersion curves.And then,based on the dispersion characteristics of surface waves,a method for separating body waves and surface waves is proposed.Finally,the separated body waves and surface waves are combined to invert the characteristics of the underground medium.This paper mainly conducts the following four aspects of research:(1)The three calculation methods of surface wave phase velocity dispersion curve are systematically sorted out: Thomson-Haskell transfer matrix method,standard δ matrix method and simplified δmatrix method.The feasibility of the algorithm is verified by calculating the Rayleigh wave phase velocities of several typical formation models.(2)In the aspect of dispersion imaging,a comparative analysis of the slant FK transform method and the multi-channel nonlinear signal processing method is carried out,and the improvement is made on the basis of the slant FK transform method,and an improved SFK transform method is proposed.Through the processing of the model and field data,the effectiveness of the new method is verified.Compared with the conventional slant FK transform method,the improved SFK transform method has an obvious effect on the extraction of high-order dispersion curves,and improves the quality of the surface wave phase velocity dispersion image.(3)According to the dispersion characteristics of the surface wave,the surface wave propagation is predicted to realize the surface wave separation.Through the processing of different models and field data,it is verified that this method can better preserve the integrity of the signal compared with the traditional frequency domain filtering method.(4)The MCMC algorithm was introduced into the joint inversion of surface waves and first arrivals,and compared with the separate inversions of surface waves and first arrivals,the advantages and feasibility of the joint inversion method were verified through the model and field data.The research results show that based on the improved SFK transform method to extract the high-resolution dispersion curve,the method in this paper can effectively realize the separation of body wave and surface wave,while retaining the integrity of the signal.And use the separated signal for joint inversion,the correct modeling of near-surface velocity can be achieved.