Pseudo-acoustic Wave Pre-stack RTM In TI Media And The Application Of The Imaging Condition

Seismic migration is an important method to determine the structure of the earth medium.Reverse time migration is based on two-way wave equation theory,is one of the most accurate migration method for the current migration method,it can adapt to the complex geological structure with strong lateral velocity variation and high inclination-angle.Although,Decades of research make traditional reverse-time migration technique that based on isotropic hypothesis not only in the aspect of theory,but also practical application are become more popular,a lot of research data show that the anisotropy widespread in the earth medium reduce the resolution of seismic migration imaging,and lead to error.Considering the limitations of the traditional reverse time migration method based on the isotropic assumption,the anisotropic pre-stack RTM method has been studied.Because there are the drawbacks of low efficiency and the difficulty of wave-field separation in anisotropic elastic wave RTM,the acoustic approximated anisotropic pseudo-acoustic wave RTM method is more advantageous.At first,this paper starting from VTI pseudo-acoustic wave equations have been studied acoustic approximated Hooke's law,equations of motion and according to the transformation of the relationship between elastic parameters and Thomsen parameters,and they are generalized to TTI media through introducing the rotation coordinate system.Then,we construct the forward and backward wave-field extrapolators by utilizing the stagger-grid high-order finite-difference scheme,and introducing the perfect matched layer(PML)boundary condition to absorb the boundary reflection energy.Finally,In order to effectively deal with a large number low frequency noise that caused by conventional cross-correlation imaging conditions migration results of medium wave field propagation path and Laplace filtering method is suppress strong energy of low frequency noise and caused filter out as part of the effective signal,the introduction of seismic detection field Angle correction to the imaging results,get an optimized normalized cross-correlation imaging conditions,we apply the optimal normalized cross-correlation imaging condition to implement anisotropic pseudo-acoustic wave RTM.With the support of the above theory and methods test to anisotropic medium homogeneous model,the anisotropic medium sag model,anisotropic medium Hess model,Model tests show that,the anisotropic RTM method can enhance the imaging quality effectively;the imaging result by optimal imaging condition is better than the conventional normalized cross-correlation imaging condition.The result shows that,according to the contrast synthetic seismogram and two kinds of algorithms of pseudo acoustic wave and isotropic acoustic wave reverse-time migration imaging.The anisotropy of earth medium effect the wave field characteristics that amplitude and of travel time,and will affect the quality of migration imaging.Therefore,in the subsequent seismic data processing and interpretation,the anisotropy factor is more and more can't be ignored,and quantitatively calculate the anisotropic parameter will also become one of the research trend.