The Study On Multiple Attenuation In Shallow Water

How to effectively suppress multiple in marine seismic exploration has been one of the important research courses.With the continuous development of offshore oil and gas exploration,multiples of the shallow water in the offshore seismic data are generally developed and harder to suppressed.The existence of these multiples has seriously affected the imaging and interpretation of seismic data.Multiple attenuation in shallow water has become the core of such seismic data processing.Since the last century,many oil companies and scientific research units in domestic and foreign have studied on how to effectively suppress multiple in detail.As a result,a variety of technical methods have been developed to suppress the multiple,which achieved very good results.Based on the principle of these techniques and the starting point to suppress the multiple,they can be divided into two categories: the filtering method which according to the analysis of the different characteristics between the primary and the multiple to suppress multiples;predictive subtraction method which based on the predictability of the multiple.Different method of multiple attenuation have different applicability,so the results of process are different.Therefore,in order to develop offshore oil and gas exploration better,it is of great significance to explore suppression technology of the multiple suitable for shallow water.In this paper,several conventional multiple attenuation methods(predictive deconvolution,Radon transform,SRME,wavefield extrapolation)are studied.The principle of various methods and the process of suppressing multiple are described respectively.At the same time,we use the data model for processing.By contrasting the result of various methods to shallow water multiples attenuation,the advantages and disadvantages of various methods for multiple attenuation in shallow water are summarized and the reasons are analyzed.Then,the prediction and subtraction method based on wavefield extrapolation is further studied.This technique belongs to the second way of suppressing multiples,which is an important method to eliminate the surface-related multiples.In view of its simple principle and well applicability,this method has been greatly promoted and used in recent years.It is divided into two steps: the first step is to predict multiple data from the velocity model or seismic data.Then,the adaptive matching method is used to reduce the predicted multiples from the original data,and the data after suppressing multiples can be obtained.However,when the wavefield extrapolation technology is used to eliminate multiples,the total wavefield information is used to predict the multiples in the seismic data by convolution with the Green's function at each point.In the process of multiple contribution gathers addition,only the energy near the stationary phase point has an effect on the summation result.In this paper,the stationary phase points in the process of adding the multiple contribution gathers are studied.Combining with the method of multiple contribution gathers and stationary phase point extraction,we find that superimposing path with multiple contribution gathers can be to optimize.The idea of stationary phase point extraction method based on the high-resolution Radon transform is put forward,which is used to superimpose the multiple contribution gather optimized aperture along the curvature of events.Compared with traditional direct stacking,the artifacts appearing around the events of the predicted multiple are well eliminated.This process reduce the influence of aliasing information on the predicted multiples model,which provide a good foundation for the adaptive subtraction of the multiple models.Therefore,the accuracy of the multiple predicted by the wavefield extrapolation and subtraction of predicted multiples in shallow water is significantly improved.By using this method,we try to suppress the multiples of shallow water in theoretical and practical ocean data.Compared with the conventional wavefield extrapolation technology,the validity and feasibility of the method are verified.