VTI介质高精度叠前逆时偏移方法研究

Investigation on high-accuracy pre-stack reverse-time migration for VTI medium

基于双程波动方程的叠前逆时偏移方法成像精度高,而且无地层倾角限制,较适合于复杂地下构造成像.但是,由于地下介质的各向异性广泛存在,基于各向同性的正演算法,尚难准确描述真实的地下波场传播,逆时偏移的成像精度也因此受到限制.鉴于此,本文研究了各向异性VTI介质逆时偏移方法,首先根据VTI介质一阶准P波方程推导出了炮点和检波点的逆时延拓的交错网格高阶差分格式,针对算法计算量和存储量大的问题,文中研究了一种改进的基于GPU加速的有效PML边界存储策略.本文建议的方法只需增加少量的额外计算,就可降低大幅度的存储成本,进而实现高精度和高效率的各向异性逆时偏移.Hess 2DVTI模型测试表明,本文提出的方法不需要存储全部历史时刻的波场,可以实现高效率高精度的VTI介质叠前逆时偏移成像.

Two-way wave equation pre-stack reverse-time migration is a kind of high-accuracy seismic imaging method which has no restrictions and is very suitable for complex structure imaging.The high-accuracy seismic wave forward modeling and reverse-time migration must consider the effect of anisotropy because of widely existing anisotropic media of the earth.This paper fully considers the problem of anisotropy and the problem of reverse time migration of large volume,large storage capacity,and studies an improved efficient PML boundary storage strategy of anisotropic VTI medium reverse time migration method based on GPU acceleration.Compared to the conventional method of reverse time migration,this method greatly reduces the storage while increases a small amount of calculation,the anisotropy reverse time migration can achieve high precision and high efficiency.On the basis of first-order quasi-P wave equation in transversely isotropic media with a vertical symmetry axis（VTI）,deduce the reverse-time extrapolation of the staggered grid high-order finite-difference scheme of shot points and receive points.In order to solve the huge amount of calculation and storage problem of reverse-time migration,we provide an improved efficient PML absorbing boundary condition based on the GPU acceleration.Test on the Hess 2DVTI model proves that this method is good for a big model and it is a high-accuracy seismic imaging method.