层状半空间地震数据的弹性波方程反演

由于叠前地震数据同时含有丰富的纵波和横波信息，而且这些信息与岩性密切相关，因此根据叠前数据的反演可以得到比常规叠后波阻抗反演更丰富、更有效的岩性信息。由于层状弹性半空间的地震波传播规律具备模拟AVO分析的条件，所以可采用一种基于弹性波波动方程的方法来合成叠前记录。文中推导了球面波在层状半空间形成的反射公式，此式包含了波前扩散效应、层状地层的横波反射及自由表面的反射，以此正演模拟算法为基础，建立了一套叠前弹性波方程反演方法，其中反演问题的求解用遗传算法完成。为了能有效地搜索到最佳地层参数，遗传算法的具体实现完全依照叠前反演这一特定的多参数非线性优化问题而设计。由叠前弹性波反演得到的纵横波速度和密度可用来计算泊松比、弹性模量等岩石物性参数，为识别储层孔隙中的流体性质提供了新手段。

Elastic wave equation inversion of seismic data in layered half-space.

Because prestack seismic data contain abundant both P-wave and S-wave information that are close relative to lithology,so more abundant and effective lithologic information can be obtained from inversion of prestack data in comparison with from ordinary poststack impedance inversion. Since propagating regularity of seismic wave in layered e-lastic half-space has condition simulating common AVO analysis,so a method based on elastic wave equation can be adopted to synthesize prestack records. The paper deduced the reflection formula formed by spherical wave in layered half-space that contains spreading effects of waveform,S-wave reflections in layered strata and reflections from free surface;taking the forward simulating algorithm as a basis,a set of prestack elastic wave equation inversion methods was built up,among which the solution of inversion problem was finished by genetic algorithm. The real implement of genetic algorithm was designed totally according to prestack inversion that is a certain optimized non-linear multi-parameters problem in order to effectively search optimum strata parameters. The P- and S-wave velocities and densities computed from prestack elastic wave inversion can be used to compute lithologic physical parameters such as Poisson ratio, elastic modulus etc. , providing new tool for identifying fluid content in reservoir pores.