VSP数据逆时偏移方法研究

Investigation on reverse-time migration of VSP data

相比于地面地震,VSP数据地震勘探具有高分辨率和高信噪比的特点,目前常规的VSP数据偏移方法难于获得理想的成像效果,逆时偏移方法(RTM)基于双程波动方程,迄今为止被认为是精度最高的地震资料偏移算法.文中依据VSP数据采集特点,从二维声波波动方程入手,研究基于高阶有限差分数值算法的VSP数据逆时偏移,数值计算采用节约部分存储的完全匹配层吸收边界条件(PML),在有效抑制地震波场的边界反射以及保持波场精度的情况下,很大程度上节约了波场存储.文中也采用了互相关成像条件以及拉普拉斯低频噪声压制技术,实现了VSP数据逆时偏移的高精度成像.测试表明,高精度的逆时偏移方法可有效成像VSP地震数据,可实现对小断层构造、大角度构造,以及井周小构造的精细刻画.

Compared with ground seismic exploration,VSP seismic exploration has the characteristics of high resolution and high signal to noise ratio.At present,conventional VSP data migration methods are difficult to obtain the ideal imaging effect.Based on the two-way wave equation,the reverse-time migration（RTM）has become the most accurate migration method so far.In this paper,on the basis of VSP data acquisition characteristics,we deal with VSP data by high order finite difference algorithm during the RTM based on 2D acoustic wave equation.We adopt the perfect matched layer absorbing boundary condition（PML）by the way of setting checkpoints,so that we saved the wave fields storage,in the meantime,effectively suppressed the boundary reflection of seismic wave fields and kept the precision.We also used the cross-correlation imaging condition and laplacian low frequency noise suppression technique to make the high resolution image with reverse-time migration of VSP data come true.The test indicated that high precision reverse-time migration could validly image VSP data and nicely depict small faults,large angle structure and the local area around the well.