基于矢量波场分离弹性波逆时偏移成像

在传统的弹性波逆时偏移中,通过Helmholtz分解获取的横波的极性随入射方向改变,导致转换波的成像值也随入射方向发生极性变化(极性反转),多炮叠加后转换波成像同相轴将受到破坏。在传统波场分离基础上,对标量势(纵波)与矢量势(横波)分别进行梯度和旋度处理,得到矢量纵波与矢量横波。针对矢量纵横波波场,引入内积成像条件进行偏移成像,通过这种成像方法无需对转换波成像进行极性校正。波场分析结果表明,该方法既适用于同类波高精度成像,也适用于转换波成像。模型实验结果表明了本文方法的正确性和适应性。

Elastic wave reverse time migration based on vector wavefield seperation

With the advances of seismic acquisition, seismic imaging has migrated from using single-component data alone to multi-component elastic wave imaging. Because of its high precision imaging ability, reverse-time migration (RTM) has been widely applied to complex structure imaging. However, S-mode polarization changes via incident direction, which will cause polarity reversal, and this polarity reversal will seriously damage the continuity of reflection events in conventional PS imaging as well as SP imaging after stacking over multiple shots. In the conventional elastic RTM, Helmholtz decomposition is used to obtain the scalar potential (P-wave) and the vector potential (S-wave). In this paper, we introduce gradient and curl operators to the scalar potential and the vector potential, respectively. Consequently, we can obtain vector P-waves and S-waves. As for the vector wavefield, we introduce an inner product imaging condition to the elastic RTM, which can avoid using extra polarity correction. Wavefield analyses show that this method is applicable not only to primary imaging (PP and SS) but also to converted wave imaging (PS and SP).The effectiveness and feasibility of our new imaging method in simple and complex models are illustrated in numerical examples using synthetic data.