Research On Diffraction Separation Techniques

With the development of fine exploration and further exploitation of structure and lithology reservoirs,as an important premise of high-precision seismic interpretation,the high resolution imaging of underground complex structure especially the small size geological objects plays an important role in the oil and gas exploration.As the main goals of the current seismic interpretation,fault,pinchout,channel,cracks,salt dome boundaries and carbonate fractured-vuggy reservoir are usually characterized by abundant diffracted waves on the seismic section.However,conventional seismic data processing technologies take the specular reflection as the main research object,while the diffraction waves are often ignored or filtered out together with noise;even though the diffraction are focused properly,the image of diffractors will also be masked by the strong amplitude of the reflection due to their low energy.As the high-resolution information encoded in diffractions is generally lost during the conventional seismic processing sequence,the imaging resolution of small-size objects underground is poor.Therefore,it is necessary to make the most use of diffraction include in the seismic data to carry out the diffraction imaging,which can improve the imaging resolution and identification accuracy of the small scale geological targets and is of important research significance and social value for the high precision seismic interpretation in the complex geological conditions.In this paper,diffraction response in different seismic gathers were analyzed,based on which different diffraction separation techniques were realized,and then two high-precision seismic imaging sequences were approached to enhance seismic identification ability and seismic interpretation accuracy of complex geological environment.This paper first studies diffraction separation and imaging method in dip angle domain,which includes the following several aspects:(1)extracte the dip-angle CIG based on the Gauss-Beam common angle migration;(2)achieve the diffraction separation method in dip angle domain based on semblance scanning,it can destruct part of the reflection event on the CIG which is located in a vicinity of the stationary apex,the diffraction imaging result can effectively highlight the diffraction energy and the imaging resolution of diffraction targets can also be improved.(3)as in the implementation of the above method,the removal radius of reflection event around its apex can only be a fixed value whether in the shallow or in the deep,which leads to the inadequate separation of the wavefield,another diffraction separation method based on reflection prediction in dip-angle domain was proposed,this method can remove the most reflection on the premise that the diffraction should be preserved well,and the corresponding diffracted image can also achieve a higher-resolution.In view of the lack of suitability for low SNR data using the dip-angle domain diffraction imaging technique,the diffraction separation and imaging method based on anti-stationary phase filtering was proposed,it applied an anti-stationary phase filter inside the conventional Kirchhoff migration operator,which can effectively attenuate events satisfying Snell's law and preserve the diffracted energy.Numerical tests showed that this technique can lead to a better resolution for diffraction objects.In addition,considering the polarity reversal of edge diffraction,a polarity correction factor is introduced in the migration kernel,which can improve the imaging quality of edge diffraction and enhance the identification accuracy of fault boundary.