考虑卷积完全匹配层数值色散的井间电磁三维正演

本文将以卷积完全匹配层为吸收边界条件的时域有限差分法应用到井间电磁的三维正演模拟中.证明了卷积完全匹配层中的数值色散会因为有效延伸因子而产生,列举常规有效延伸因子和网格间距对电磁波相速度各向异性的影响,并通过波场快照验证卷积完全匹配层中数值色散的存在;进而推广三维卷积完全匹配层中最大有效延伸因子、最大网格间距与激励源主频之间的约束,以此完善卷积完全匹配层的最优参数设置方案.在此基础上,通过正演结果中二次场的垂直磁场分量和走时来展示灵敏度分布,以此划定井间电磁勘探的优势区域,提出井间电磁正反演所需要的约束测井系列和最佳取井方案.

Three-dimensional cross-well electromagnetic modeling considering numerical dispersion in convolutional perfectly matched layers

Taking Convolutional Perfectly Matched Layers (CPML) as the absorbing boundary conditions, this paper applied Finite-Difference Time-Domain (FDTD) into 3D modeling of cross-well electromagnetic (CWEM). The study proved that it was the real stretch which induced numerical dispersion in CPML, given the anisotropy effect of phase velocity of electromagnetic wave from the conventional real stretch and grid interval, and verified numerical dispersion in CPML through wave field snapshot; further on, generalized the restriction between the dominant frequency of source and maximum of real stretch, maximum of grid interval in CPML, so as to improve optimal parameter settings in CPML. Based on optimal CPML, we utilized the vertical magnetic field and the traveling time of second field to describe the distribution of sensitivity, so as to designate the dominant area of cross-well electromagnetic prospecting, and proposed the logging suite for restraint and preferred plan for selecting well which were required in the process of the modeling and inversion of cross-well electromagnetic.