绕射波逆时偏移成像方法研究

地震剖面中的绕射点反应地下断层、尖灭、溶洞等不连续体的位置信息，因此绕射波对于实现小尺度构造的精细成像具有重要意义.基于逆时偏移的绕射波成像方案包括乘法成像条件法和倾角域拾取法.乘法成像条件利用正负倾角构造剖面相乘实现绕射点的定位，倾角域拾取法则根据绕射波能量在角度域的特征进行拾取.其中，通过Hilbert变换和伴随波场的延拓可以实现波场的方向分解，从而实现单一倾向构造的成像并改善倾角道集的质量.本文也对无需方向分解的正负倾角构造成像公式进行了推导.逆时偏移作为一种全波成像方法，所得剖面本身包含绕射点信息，因此本文通过图像处理方法提取绕射点位置.这一方法具有成本低、扩展性强、可对剖面做局部化处理的特点.

Research on diffraction wave reverse time migration imaging methods

Diffraction points in the seismic profile reflect the location information of discontinuities such as underground faults, pinching-outs, and karst caves. Therefore, the diffracted wave is of great significance for the realization of precise imaging of small-scale structures. The diffracted wave imaging schemes based on reverse time migration include the multiplication imaging condition-based method and the picking-up method in the dip-angle domain. The multiplication imaging condition-based method locates diffraction points by multiplying positive- and negative-dip angle structural profiles. And the basis of the picking-up method are characteristics of the diffracted wave in the dip angle domain. Among them, we achieve the wavefield directional decomposition with the help of the Hilbert transform and the extrapolation of the accompanying wavefield, thus realizing the imaging of structures in an inclined direction and improving the quality of the dip gathers. We also derive the imaging conditions for positive- or negative-dip angle structures which don't need directional decomposition. As a full-wave imaging approach, reverse time migration provides an imaging profile including diffraction points, which inspires us to extract the diffraction points' locations from the seismic profile through image processing. Compared with the previous two methods, this method has the characteristics of low cost, robust scalability, and localized profile processing.