基于VTI介质的隧道超前探测qP波正演模拟研究

Forward Modeling of Tunnel Advanced Detection qP Wave Based on VTI Medium

由于隧道超前探测的环境与常规石油地震勘探的差异,不宜直接将过去的模拟方法拿到隧道中进行应用。结合层状地层表现出横向各向同性的特性,推导出在隧道空间适用的二维VTI介质一阶qP波方程,分析了其稳定条件。建立断层和软弱夹层的几种数值模型,利用PML边界解决模型边界反射,采用交错网格进行有限差分正演模拟,得到其共炮点道集。结果表明,qP波有限差分法可以快速地模拟不良的地震响应,规避伪S波和数值不稳定问题,为隧道超前探测资料的解释提供依据,提高预测的准确性。

Due to the difference between the environment of tunnel pre-detection and conventional petroleum seismic exploration,it is not appropriate to directly apply the past simulation method to the tunnel.Combined with the transverse isotropy characteristic of layered stratum,the first-order qP wave equation of the two-dimensional VTI medium suitable for tunnel space was derived,and the stability conditions were analyzed.Several numerical models of fault and weak interlayer were established.The boundary reflection of the model was solved by PML boundary,and the finite difference forward modeling was carried out by staggered grid to obtain the common shot gather.The results show that the qP wave finite difference method can quickly simulate the bad seismic response,avoid the pseudo S wave and numerical instability problem,and provide a basis for the interpretation of tunnel advance detection data to improve the accuracy of prediction.