Research On The Separation Of P-and S-wave For Multi-component Crosswell Seismic Data

Crosswell seismic technique as a high resolution exploring technique becomes more and more usefull in the petroleum exploitation and produce.In the crosswell seismic data processing, we mainly use the seismic tomography with directed wave and obtain high resolutional stack section with reflected wave.In traditional processing techniques of the two methods,we generally use the s-wave only,not considering the s-wave.One side,it's caused by our inadequate understand on S-wave,on the other hand,s-wave is more complicated than p-wave. The energy of the s-wave is very low and is covered by p-wave,so we can't extract s-wave from multiple waves easily.Today,the seismic exploration has developed from single structure exploration to structure lithology exploration,and we now can resolve a few problems about S-wave.If we can obtain the s-wave data from originality wavefield exactly,then we can obtain the S-wave velocity field of the medium between the stimulate well and receive well.This is very important and usefull to investigate the physical property of the stratum(lithology,porosity,fluid component,et al.).So,the separation of s-wave and s-wave from crosswell seismic data is absolute significant in the crosswell seismic processing.This article is based on the characteristic of the crosswell seismic wavefield,and give the steps of the separation of p-wave and s-wave.Firstly,make filtering techniques on originality multi-component data,and we can eliminate many coherent interference waves.If the originality seismic data is three components,we should transform them to two components using vector synthesis method.Secondly,with the vertical component and horizontal component,we must separate the down-going wave from up-going wave.Thirdly,with the separated down-going wave and up-going wave,we can calculate the polarization angle by covariance matrix.Fourthly, applying the polarization angle on the wavefield separation matrix,then we can separate the s-wave from p-wave for both up-going wave and down-going wave.Lastly,adding the up-going s-wave and down-going s-wave as the final s-wave,and adding the up-going p-wave and down-going p-wave as the final p-wave.When separating the up-going wave from down-going wave,we use the frequency-space domainτ-p transform.The using of generalized inverse and the trimming treatment can suppress false frequency and port effect effectively.Using the singular value decomposition method,we can improve calculation efficiency obviously.We found the covariance matrix to calculate the polarization angle.This technique don't need velocity information,and we should justly enter the the up-going wave and down-going wave of two components.When founding the covariance matrix,the choosing of the time window is very important,and this article introduce two ways to choose the time window,the autocorrelation and passing zero point.Then,we found the wavefield separation matrix,and put the polarization angle in it,which is calculated above.We call this method for polarization rotation,and after this,the separation of p-wave and s-wave is complete.The tests on the stimulant theoretically crosswell seismic data and practicality data denote:in the final p-wave profile,the energy of s-wave is subdued,and the p-wave is reserved,in the final s-wave profile,the great mass of p-wave is eliminated,and the s-wave which is formerly covered by p-wave appears out distinctly.In the article,the method to separate the p-wave from s-wave for crosswell seismic data works effectively.This method adequately use the polarization characteristic and apparent velocity characteristic,and it calculate rapidly with strong anti-noise ability.Besides,after properly process,it can be applied in surface and marine seismic records.