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在高阶有限差分法逆时偏移成像过程中,成像精度和计算效率是一对矛盾体,特别是对于小尺度细微地质构造的刻画。为了能在精细刻画局部地质体结构的同时,保证逆时偏移的计算效率,采用多尺度可变网格有限差分算法求解一阶应力-速度声波方程,将可变网格有限差分算法引入到逆时偏移中,对传统常规逆时偏移算法进行了改进,并将可变网格步长倍数的变化范围推广至任意奇数倍,分析了可变网格对有限差分算法数值频散的影响。不同模型偏移成像试验结果表明,可变网格逆时偏移算法能在保证地下地质体成像精度的同时提高偏移效率,有利于局部构造特征的精细刻画。
In high-order finite-difference finite-difference method of inverse time migration imaging, imaging accuracy and computational efficiency are a pair of contradictions, especially for small-scale fine geological structure characterization. In order to ensure the calculation efficiency of inverse time migration while finely describing the local geological body structure, the first-order stress-velocity acoustic wave equation is solved by the multi-scale variable mesh finite difference algorithm, and the variable mesh finite difference algorithm is introduced into In the reverse time migration, the traditional conventional inverse time migration algorithm is improved, and the range of the variable multiple of the variable grid is extended to any odd multiple. The numerical analysis of the numerical dispersion of the finite difference algorithm by the variable grid influences. The experimental results of different model migration imaging show that the variable grid inverse time migration algorithm can improve the migration efficiency while ensuring the imaging accuracy of the underground geological body, which is propitious to the fine characterization of the local tectonic features.