基于TTI介质的VSP纵横波数据逆时偏移方法研究

This project intends to study the reverse-time migration for both the vertical seismic profiling (VSP) compressional and shear waves in tilted transversely isotropic (TTI) media. This research is the basic and important component for joint application of borehole and surface seismic data in oil and gas exploration and development, and is also the key technology in the current academic research and industrial practices. In order to derive the decoupled quasi-P and quasi-SV wave equations for TTI media and to conduct stable reverse-time migration, this project: 1)Uses the method of undetermined coefficients and the technique of parameter scanning to obtain high-accurate approximation of the phase velocities, and further to derive a set of high-accurate decoupled P and SV wave equations for TTI media; 2)Presents an efficient iterative finite-difference (FD) solution for the new P and SV wave equations, whose temporal and spatial differential operators are coupled. The new solution does not need to solve a high-order sparse linear system. And gives the absorbing boundary and stability conditions for modeling; 3) Uses the new decoupled wave equations and the new iterative FD solution to implement reverse-time migration for VSP reflected and converted waves, respectively, in TTI media, and proposes the method of "constraining by wave fields of a small quantity of time steps" to decrease the disk size for data saving and the method of "layer-by-layer migration" to suppress migration noises.

项目研究各向异性TTI介质（即具有倾斜对称轴的横向各向同性介质）垂直地震剖面（VSP）纵、横波数据的逆时偏移成像。这是井地联合用于油气田勘探和开发的基础而重要的研究内容，也是当前学术及工业界正研究的一项关键技术。 为导出各向异性介质条件下的纯准纵波和准横波方程，并由此实现稳定的逆时偏移成像，本项目：1）采用待定系数法和参数扫描技术实现各向异性介质相速度的高精度近似，进而推导出一组高精度的TTI 介质纯纵波和纯横波方程；2）研究一种针对所推导时空微分耦合波动方程的有限差分解法，提出一种"迭代有限差分"方法，可避免常规有限差分解法所需要的大型稀疏矩阵线性方程组求解，提高计算效率，并给出相应的边界处理方法和稳定性条件；3）用所推导的方程和所提出的解法实现TTI介质VSP纵、横波数据的各自逆时偏移成像，并提出减小逆时偏移所需硬盘存储量的"少量时间步波场约束"法以及压制偏移噪音的"逐层偏移"法。