基于最优Born近似的叠前深度偏移方法

波动方程法中的叠前深度偏移是实现复杂构造和岩性地震成像的关键技术。其中 ,广义屏法是近几年发展起来的一种新方法 ,它基于散射理论、屏近似和一般Born近似 ,具有较高的精度和效率 ,是条件稳定的。为了提高算法的稳定性 ,提出了基于最优Born近似的叠前深度偏移方法。即对散射波场成像所使用的介质速度横向扰动公式不做任何近似 ,并且采用与两个延拓深度层中间位置处的地震波场最接近的波场代替层间的平均波场 ,而不是用上一延拓层处的地震波场代替层间的平均波场。模型试算结果表明 ,最优Born近似法对复杂地质体具有较强的适应性 ,在保证计算效率和成像精度的前提下 ,明显提高了算法的稳定性。

A prestack depth migration method based on optimized born approximation

The prestack depth migration in the wave equation is a key technique to realize the seismic imaging of complex structure and lithology. The generalized screen(GS)method is a new one in this technique and developed on the bases of scattered theory, screen approximation and general Born approximation. The GS method has a high imaging accuracy and computing efficiency, and its conditions are stable. In order to improve the stability of the algorithm, a prestack depth migration method based on the optimized Born approximation was proposed. The optimized Born approximation has the following feature. (1) It need not make any approximation for the lateral perturbation formula of medium velocity for imaging the scattered wave field. (2) The internal average wave field may be replaced with the seismic wave field, which can optimally approximate the seismic wave field in the medium of two continuation depth layers, instead of doing that at the last continuation depth layer. The tests of the model show that the optimized Born approximation method can qualify the effectiveness and adaptability to complex geological body, and can obviously improve the stability of the algorithm under the conditions for ensuring the computation efficiency and imaging accuracy.