基于自适应非规则三角网格的地震TI介质多波反射走时层析成像研究

The rock and stratum have apparent anisotropic property in natural world. Hence, the inversion results of the anisotropic seismic traveltime tomography can reflect the true attribute of the underground medium better. There are 3-7 anisotropic parameters to be inverted by this method, this suggest that the inversion results are much more uncertain than the inversion results of isotropic inversion method. The adaptive irregular grid algorithm can describe the details of geological model better. Besides, it can adjust the locations and density distribution of the grid nodes, according to the observation system, acquired data quality, ray density distribution and velocity variations. It can enhance the resolution and reliability of the inversion results by use of optimal grid model which can reduce the null space energy elements in the tomographic matrix. Seismic multiwave traveltime tomography also can improve the resolution and reliability of the inversion results by use of the ray paths and traveltimes of different kinds of waves. According to these advantages of the two kinds of algorithm, this project aims to research of the seismic multiwave reflection ray tracing algorithm based on adaptive irregular triangular grids, and further implementation of seismic multiwave reflection traveltime tomographic algorithm for anisotropic TI medium base on adaptive irregular triangular grids. Then, perform numerical simulation and analysis for simple and complex geological models. It has very important theoretical significance and practical application value of the project, because it can prompt the research of the anisotropic ray tracing method and seismic traveltime inversion method.

自然界的岩石和地层存在明显的各向异性性质，各向异性地震走时层析成像反演结果更能够反映地下介质的真实属性。但是其反演结果通常为3-7个各向异性参数，因此它相对各向同性介质反演结果具有更强的不确定性。自适应非规则网格算法可以更好地刻画地质模型信息，还可以根据观测系统分布、数据采集质量、射线密度分布和速度变化情况，调整网格节点的位置和密度分布，利用最佳网格分布减少层析成像矩阵内部的零空间能量元素，从而提高反演结果的精度和可靠性。地震多波走时反演算法利用各种波的射线分布和走时观测信息也能够增强反演结果的精度和可靠性。本项目拟结合这两种算法优点研究出自适应非规则三角网格地震多波反射射线追踪算法，进一步实现各向异性TI介质自适应非规则三角网格地震多波反射走时层析成像算法，并对简单和复杂模型进行数值模拟和分析。该研究对各向异性介质射线正演模拟和各向异性参数反演具有非常重要的理论意义和实际应用价值。

自然界岩石和矿物均存在各向异性性质，地层各向异性性质的强弱不一，传统的弱各向异性性质假设的适用范围有限，因此采用弹性模量参数（C11, C13, C33, C44, C66, θ0, φ0）能够表征不同各向异性强度大小的地层。本项目结合自适应非规则网格算法和最短路径算法实现了TI介质qP、qSV和qSH波的走时和路径计算方法。然后，利用非线性共轭梯度算法和层析成像方程实现了TI介质qP、qSV和qSH波的走时层析成像，反演得到了一套完整的弹性模量参数。同时，为加快TI介质qP、qSV和qSH波走时的计算效率，结合迎风有限差分法和快速扫描法，实现了多波走时快速计算方法；为提高TI介质qP、qSV和qSH波走时的计算精度，结合因式分解法和快速扫描法，实现了多波走时高精度计算方法。TI介质qP、qSV和qSH波走时的高效、高精度计算方法，以及基于最短路径的TI介质弹性参数反演方法，为将来实现一般各向异性介质的高维、高效、高精度的走时层析成像奠定了坚实的基础。该研究可以运用于天然地震和勘探地震领域的各向异性参数反演，其具有非常重要的理论意义和实际应用价值。