井中和井间地震波场正演模拟

Borehole and crosshole seismic wave field forward modeling

（中国地质大学（武汉）地球物理与空间信息学院，湖北武汉430074）

Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan 430074, China

研究井中和井间地震波场的形成过程以及波场分量的转换规律，对于指导实际井中地震测量工作有着十分重要的意义。为此，采用变间距交错网格有限差分方法，进行了单井慢速地层和快速地层半空间模型以及井间快速地层半空间模型的地震波场正演模拟。给出了方法的基本原理，讨论了算法的边界条件和自由界面问题，阐述了可变空间步长和可变时间步长的实现方法。采用变间距交错网格、完全匹配层吸收边界条件和Xu等提出的利用声学和弹性介质界面近似代替自由界面的方法，很好地模拟了波场的形成过程，获得了信息丰富的弹性波波场快照。对模拟结果进行了分析，认为井间地震记录是各类波组干涉的结果。

Study on the build-up process of borehole and crosshole seismic wave field and transformation rule of wave field components is important for guiding actual logging. Therefore, the finite-difference method with variable grid and variable-space staggered grid is used for seismic wave field forward modeling on single borehole semi-spatial model with soft formation and fast formation, as well as crosshole semi-spatial model with fast formation. Firstly, the basic principles are given. Then, the boundary conditions and free interface of the algorithm are discussed. Some methods (including staggered grid with variable time step, perfectly matched layer absorption boundary conditions, the free interface approximately replaced by acoustics and elastic medium interface proposed by Xu et al) were used to effectively stimulate the build-up process of wave field and obtain elastic wave field snapshot with abundant information. The simulated result was analyzed; it is thought that the seismic logging record is the interference result of all kinds of wave groups.