基于行波分离和角度域衰减的地震波叠前逆时成像条件

Seismic Wave Pre-Stack Reverse-Time Migration Imaging Condition Based on One-Way Wave Field Separation and Angle Domain Attenuation

为提高陡倾角复杂构造区地震波逆时成像质量,提出一种逆时偏移成像条件.以二维模型为例,采用波印廷矢量实现方向行波的波场分离和地层反射角度的计算,将炮点和检波点的上行波场和下行波场、左行波场和右行波场两两作互相关计算,去除形成逆时偏移噪声的分量,同时将反射角度的余弦函数作为权函数引入互相关逆时成像条件中,进一步实现角度域逆时噪声的衰减.研究表明,炮点和检波点相反传播方向波场的互相关计算是形成偏移噪声的主要原因,相同传播方向的行波波场两两作互相关成像并组合叠加,可以在有效压制偏移噪声的同时,保持对陡倾角和水平界面的成像能力,再在角度域实现逆时噪声衰减,进一步提高逆时成像质量,实际地震资料验证了方法的有效性.所提的逆时成像条件可为复杂构造区高精度逆时成像提供重要的方法指导.

To improve seismic wave reverse-time migration （RTM） quality of complex structures, a new RTM imaging condition is shown. Take 2D model as example, one-way wave field and formation reflection angle with Poynting vector are obtained. Correlation calculation between up-way and down-way wave field, and between left-way and right-way wave field of shot and receiver are made, which removes migration noise components. Further, it introduces weight of cosine function of reflection angle into cross-correlation RTM imaging condition to suppress noise. Model study shows that main cause of migration noise is cross-correlation image of different shot and receiver point propagating direction wave field. Cross-correlation image of same shot and receiver point propagating direction wave field can suppress migration noise effectively and maintain imaging ability on sharp angle layer and horizontal surface as well. Imaging results can be further improved with weight of cosine function. Practical seismic data verify the method. In summary, the imaging condition provides an important method guide for improving imaging quality in complex structure area.