基于一步法波场延拓的正演模拟和逆时偏移成像

通常工业界实现逆时偏移算法时采用有限差分数值方法模拟地震波场,波场模拟常常受稳定性条件限制,且易产生数值频散,成像精度降低.本文引入了一步法波场延拓方法,首先构建声波传播算子,借助Chebyshev多项式和Jacobi-Anger展开式近似传播算子中的e指数项,进而实现波场递推,该方法时间步长的选取不受稳定性条件限制而且不存在空间频散现象.本文将一步法波场延拓方法用于逆时偏移成像的波场模拟,并提出双缓冲区存储策略,在不增加计算量的前提下,大幅降低了逆时偏移方法的波场存储量.波场模拟和逆时偏移成像测试表明,本文提出的一步法波场延拓方法模拟地震波场精度高,消除了频散影响,可在较大时间步长的情况下实现高精度波场模拟;提出的基于一步法波场延拓的逆时偏移方法成像质量好;基于双缓冲区存储策略的逆时偏移成像方法存储成本低.

Forward simulation and reverse time migration imaging based on one step wavefield extrapolation

In industry application, wavefield simulation with finite difference numerical method is always applied for reverse time migration algorithm. But the above approach is limited by stability conditions and numerical dispersion, which would reduce the imaging precision. In this paper, we introduced one step wavefield extrapolation method. Firstly, we constructed the acoustic propagation operator, then approximated the exponent item in the propagation operator by Chebyshev and Jacobi-Anger polynomial expansions to accomplish the wavefiled extrapolation algorithm. The proposed wavefield simulation algorithm is unconditionally stable in the chosen of time-step size and free of the numerical dispersion. We exploited one step method to the wavefield simulation of reverse time migration, then we proposed a Duo-buffer storage strategy, which can reduce the wavefield storage content obviously without computation increase. Examples of wavefield simulation and reverse time migration show that: 1. the proposed one step method could extrapolate wavefield accurately, be free of dispersion noise for large time-step size; 2. the one step method can be well applied to the reverse time migration algorithm; 3. the proposed Duo-buffer storage strategy could highly reduce the wavefield storage of reverse time migration based on one step method.