Research On Seismic Wave Field Simulation And Reverse Time Migration In VTI Medium

At present,the geological targets of oil and gas exploration are highly complex,and isotropy research can no longer meet the accuracy requirements of conventional underground exploration,so it is urgent to further characterize the characteristics of the actual underground medium.Therefore,the reverse time migration method based on the two-way wave equation is considered to be one of the most accurate imaging methods at present,but its imaging results can only depict the structural morphology.The physical properties of the reservoir cannot be characterized.On the basis that inverse time migration can accurately image complex structures,this thesis mainly studies the wave field simulation,inverse time migration imaging and imaging conditions involved in the inverse time migration in VTI media.The main research progress is as follows:(1)The forward simulation of VTI medium is carried out by using finite difference method and pseudo-spectral method respectively,and the comparison between VTI medium and acoustic medium is tested.On this basis,the multiple-angle expansion wavefield simulation method of the two-dimensional VTI decoupling equation is derived by the multiple-angle method.The Taylor series expansion and multiple-angle parameters are used to approximate the analytical solution of the two-dimensional VTI wave equation,and then the wavefield simulation is carried out.The parameter selection of this method has high tolerance and no pseudo dispersion interference,and the stability is well.(2)The CPU/GPU collaborative computing technology is used to realize the twodimensional VTI decoupling wavefield simulation method and reverse time migration method,which improves the efficiency of Fourier transform.(3)The multiple-angle wavefield simulation method of two-dimensional VTI decoupling equation is further extended by using the Hilbert transform method,and the wavefield is separated into up and down going wavefield,forming the going wave separation method of multiple-angle expansion method in VTI medium.(4)The seismic wavefield numerical simulation test andgoing wave separation test are carried out by using a variety of two-dimensional velocity models,and the reverse time migration test is carried out by cross-correlation imaging condition.The results show that the proposed method can achieve stable wavefield simulation under the condition of large time step,and can be successfully applied to going wave separation method and reverse time migration method,and the imaging results are real and reliable.The proposed method framework can be transplanted to high-performance computing cluster,and has great industrial application potential.