Extraction Algorithm Of Angle Domain Common Image Gather Based On Pre-stack Wave-equation Depth Migration

Pre-stack wave-equation depth migration is an effective technique for seismic imaging of deep complex structure. But its image accuracy varies across the precision of initial velocity model, the signal-to-noise ratio of raw data and the accuracy of wave-field continuation operator. In order to provide migration velocity analysis with better, feint-free common image gathers and get the accuracy of seismic migration imaging improved, the Fourier Finite-difference wave-field continuation operator and several kinds of common image gathers were discussed in this paper. Further more, a method of extracting angle-domain common-imaging gather (ADCIG) after seismic imaging was proposed.Wave-field continuation operator can affect the accuracy of seismic migration imaging; it's also the prerequisite of extracting Angle-domain common-image gather after imaging. During the process of wave-field continuation, this operator will automatically switches between the frequency-wave number domain which is more suitable for imaging of high-angle faults and the frequency-space domain which is more suitable for imaging of strong lateral velocity variation medium.Angle-domain common-image gather, know as a feint-free common image gather, is also testified to be the optimal substitution for ordinary common image gather when applied on Migration Velocity Analysis(MVA) or Amplitude Versus Angle(AVA) analysis. Based on the previous studies, this paper presented a method for computing angle-domain common-image gather from seismic images. Different from extracting angle-domain common image gather before imaging, our method produces the output as a function of the reflection angle, not as a function of offset ray parameter. Further more, this method is fast, robust and easy to implement. The key moves are listed below: 1) using Fourier Finite-difference wave-field extrapolation operator to perform the wave-field continuation; 2) imaging the extrapolation wave-filed near the imaging point with the non-zero offset imaging condition and then extracting offset-domain common-image gather; 3) using slant stack technology to convert the offset common image gather into angle domain common image gather. Numerical testing shows that this method can extract the angle domain common image gather successively and can provide Migration Velocity Analysis with optimal raw data.